k ˉ \bar k k ˉ R ˉ \bar R R ˉ Δ T \Delta T Δ T V ˉ \bar V V ˉ Δ z \Delta z Δ z contour interval — the difference in depth between neighbouring contours, m Geoscience · Stress, strain and structural analysis contour interval, the thickness of the slice, m Geoscience · Gross rock volume from maps depth interval between samples transmitted in real time, m Logs and petrophysics · Open-hole logging: why, how and when sampling interval in depth, m Logs and petrophysics · Gamma ray log and natural gamma ray spectrometry permissible averaging over depth (the desired vertical resolution), m Logs and petrophysics · Nuclear magnetic resonance (NMR) logging vertical distance between the probes, m Well testing · Supercharging and permeability from formation-tester pretests constant error of the depths of the well: by how much the recorded depths are less than the true ones, m Well testing · Forced-gradient technique and multi-well analysis rise of the current FWL relative to the initial one, found from pressure, m Well testing · Two-phase flow and reservoir description from formation-tester data vertical height of the column, m Drilling · Pore pressure and overburden pressure Δ p \Delta p Δ p excess of the pressure in the salt beneath the minibasin over the pressure in the salt beneath the dome, at the same depth z 1 z_1 z 1 , Pa Geoscience · Folds, salt diapirs and their relationship to faults pressure drop across the cake (approximately equal to the overbalance), Pa Logs and petrophysics · Borehole environment: invaded zone and mudcake difference between the hydrocarbon pressure at the top and the water pressure extended along its gradient to the same depth, Pa Reservoir engineering · Reservoir pressure and temperature pressure drop across the capillary, Pa Reservoir engineering · Laboratory PVT tests fall of the reservoir pressure, p i − p p_i - p p i − p , MPa Reservoir engineering · Rock compressibility and the effect of stress on core properties fall of the reservoir pressure, MPa Reservoir engineering · Rock compressibility and the effect of stress on core properties fall of the pore pressure, MPa Reservoir engineering · Rock compressibility and the effect of stress on core properties exact pressure fall p i − p p_i - p p i − p , Pa Reservoir engineering · Diffusivity equation pressure drop relative to the initial pressure, p i − p ( x , y , t ) p_i - p(x, y, t) p i − p ( x , y , t ) x x x y y y t t t , Pa Reservoir engineering · Superposition principle fall of the average reservoir pressure from the initial pressure, MPa Reservoir engineering · Reservoir drive mechanisms fall of the average reservoir pressure from the initial one, p i − p p_i - p p i − p , MPa Reservoir engineering · Material balance for gas reservoirs fall in the average reservoir pressure from its initial value, p i − p p_i - p p i − p , MPa Reservoir engineering · General material balance equation for oil reservoirs fall in pressure from the initial value, p i − p p_i - p p i − p , MPa Reservoir engineering · Performance prediction for solution gas drive reservoirs pressure drop at the contact, constant from the moment t = 0 t = 0 t = 0 , MPa Reservoir engineering · Aquifer models: water influx pressure difference between the rows of injection and production wells, common to all the layers, Pa Reservoir engineering · Displacement in heterogeneous reservoirs pressure decline p i − p p_i - p p i − p , Pa Well testing · Dimensionless well solutions: skin, radius of investigation and units pressure decline p i − p p_i - p p i − p r r r , Pa Well testing · Dimensionless well solutions: skin, radius of investigation and units change of the bottomhole pressure since start-up or shut-in: p i − p w f p_i - p_{wf} p i − p w f p w s − p w f ( Δ t = 0 ) p_{ws} - p_{wf}(\Delta t = 0) p w s − p w f ( Δ t = 0 ) , Pa Well testing · Wellbore storage change of the bottomhole pressure since start-up (p i − p w f p_i - p_{wf} p i − p w f p w s − p w f ( Δ t = 0 ) p_{ws} - p_{wf}(\Delta t = 0) p w s − p w f ( Δ t = 0 ) , Pa Well testing · Type-curve matching change of the bottomhole pressure since start-up or shut-in: p i − p w f p_i - p_{wf} p i − p w f p w s − p w f ( Δ t = 0 ) p_{ws} - p_{wf}(\Delta t = 0) p w s − p w f ( Δ t = 0 ) , Pa Well testing · Diagnosis with the pressure derivative drop in bottomhole pressure p i − p w f p_i - p_{wf} p i − p w f , Pa Well testing · A sealing fault near the well: the method of images drop of the bottomhole pressure, p i − p w f p_i - p_{wf} p i − p w f , Pa Well testing · Semi-infinite systems: theory and test analysis pressure rise after shut-in: p w s ( Δ t ) − p w f ( Δ t = 0 ) p_{ws}(\Delta t) - p_{wf}(\Delta t = 0) p w s ( Δ t ) − p w f ( Δ t = 0 ) , MPa Well testing · Equivalent producing time and synthetic flowing time pressure difference between the inlet and outlet faces, Pa Simulation · Permeability upscaling for single-phase flow overbalance: the mud pressure minus the pore pressure at the same depth, MPa Drilling · Bit selection and dull grading fall of the bottomhole pressure, Pa Drilling · Well control: primary barrier and kick indicators fall of the pressure of the column in the annulus, which must be made up by the wellhead pressure, Pa Drilling · Well kill methods pressure drop across the choke; if the pressure downstream of the choke is close to atmospheric, it is the annulus pressure at the wellhead, Pa Drilling · Blowout prevention equipment fall of the pressure on the formations of the open hole, Pa Drilling · Wellheads and running casing pressure difference across the cake, Pa Drilling · Field testing of drilling fluids pressure difference, Pa Drilling · Field testing of drilling fluids pressure drop across the motor, the difference between the pressures at the inlet and the outlet, Pa Drilling · Deflection tools and downhole motors drawdown p ˉ R − p w f \bar p_R - p_{wf} p ˉ R − p w f , Pa Production · Acid treatments: principle, economics and candidate selection bottomhole pressure drop after start-up at a constant rate, Pa Production · Inflow to a hydraulically fractured well pressure difference between the fracture and the reservoir, Pa Production · Fracturing fluids and tip-screenout fracturing Δ V \Delta V Δ V Δ t \Delta t Δ t increase in vertical throw during the accumulation of the unit, m Geoscience · Structural styles and tectonic history time from the end of circulation to the measurement, h Logs and petrophysics · Formation water and formation temperature interval transit time, µs/m Logs and petrophysics · Sonic log interval transit time of the rock at the borehole wall, µs/m Logs and petrophysics · Sonic log interval transit time of the rock, averaged over the span, µs/m Logs and petrophysics · Sonic log interval transit time from the log, µs/m Logs and petrophysics · Porosity from the sonic log interval transit time of the rock, µs/m Logs and petrophysics · Porosity from the sonic log interval transit time from the sonic log, µs/m Logs and petrophysics · M–N and MID plots for complex lithologies time, d Reservoir engineering · Why water is injected: pressure maintenance and oil displacement time since shut-in, h Well testing · Pressure build-up analysis time after shut-in, s Well testing · Effect of producing time on build-up analysis required shut-in duration, h Well testing · Effect of producing time on build-up analysis time step, d Simulation · What a reservoir simulation model is and why it is needed time of a step, s Drilling · Bit performance and cost per metre time after the end of injection, min Production · Rock mechanics for hydraulic fracturing length of the averaging period (a day, a month), d Production · Water injection systems the delay; divide months by 12, years Economics · State regulation of field development length of the period: a month is 1 / 12 1/12 1/12 1 / 252 1/252 1/252 , years Economics · Market, financial and regulatory uncertainty Δ H \Delta H Δ H Δ q \Delta q Δ q Δ s \Delta s Δ s x ˉ \bar x x ˉ p ˉ \bar p p ˉ reservoir pressure in the drainage area, MPa Reservoir engineering · Reservoir fluid sampling mean pressure in the sample, ( p 1 + p 2 ) / 2 (p_1 + p_2)/2 ( p 1 + p 2 ) /2 , atm or MPa Reservoir engineering · Rock permeability pore-volume-averaged pressure in the drainage area, MPa Reservoir engineering · Flow regimes average reservoir pressure, MPa Well testing · Well inflow: the well performance diagram pressure averaged over the pore volume of the drainage area, Pa Well testing · Steady-state radial flow average reservoir pressure : the pressure averaged over the pore volume of the area, Pa Well testing · Pseudo-steady-state flow and the shape factor pressure averaged over the pore volume of the area, Pa Well testing · Pseudo-steady-state flow and the shape factor average pressure in the drainage area in pseudo-steady-state flow, Pa Well testing · Skin factor average pressure of the area at the moment of shut-in, Pa Well testing · Build-up in a bounded reservoir and average reservoir pressure average pressure in the block, Pa Production · Horizontal wells reservoir pressure in the injection area, Pa Production · Sources of formation damage reservoir pressure, Pa Production · Acid systems and treatment design average (current) reservoir pressure, MPa Production · Sand production: types, prediction and cost of the problem Δ h \Delta h Δ h Δ x \Delta x Δ x Δ L \Delta L Δ L Δ F \Delta F Δ F p ˉ , p w f \bar p,\ p_{wf} p ˉ , p w f d p / d z \dd p/\dd z d p / d z 0.809 0.809 0.809 a a a thickness of the lithosphere before stretching; typically 125 km, m Geoscience · Plate tectonics and sedimentary basins spacing of the points from which the curvature is calculated, m Geoscience · Practical structural geology radius of the sphere, m Geoscience · Geophysical exploration methods range: for the spherical model, the distance at which it reaches the sill; for the exponential and Gaussian models, the distance at which it reaches 95% of the partial sill, m Geoscience · Spatial correlation and the variogram smallest possible value, units of the parameter Geoscience · Probabilistic volumetrics by Monte Carlo simulation gap between the tool and the wall, m Logs and petrophysics · Sonic log calibration coefficient, mD/ms² Logs and petrophysics · Nuclear magnetic resonance (NMR) logging tortuosity factor (how winding the paths are), an empirical coefficient, — Logs and petrophysics · Archie's equation and saturation of clean reservoirs constant of the attraction between molecules, MPa·m⁶/kmol² Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) attraction parameter, MPa·m⁶/kmol² Reservoir engineering · Cubic equations of state a coefficient fitted to the measurements, — Reservoir engineering · Reservoir fluid sampling approach constant: at the time t t t a / t a/t a / t , s Well testing · Several boundaries: parallel faults and wedge-shaped blocks a constant (it depends on the shape of the area and the production history), Pa Well testing · Build-up in a bounded reservoir and average reservoir pressure volume of gas at atmospheric pressure per unit volume of mud, ρ m / ρ s − 1 \rho_m/\rho_s - 1 ρ m / ρ s − 1 , — Drilling · Well control: primary barrier and kick indicators acceleration: gravity g g g ω 2 r \omega^2 r ω 2 r , m/s² Drilling · Solids control in drilling fluids semi-major axis of the drainage ellipse with its foci at the ends of the wellbore and the area of a circle of radius r e h r_{eh} r e h , m Production · Horizontal wells viscous flow resistance coefficient; includes the effect of the skin factor, MPa²/(thousand m³/d) Production · Inflow performance relationship (IPR) rate of decline of the gain: Δ q ( t ) = Δ q 0 e − a t \Delta q(t) = \Delta q_0\,\e^{-at} Δ q ( t ) = Δ q 0 e − a t ln 2 / a \ln 2/a ln 2/ a , 1/d Production · Acid treatments: principle, economics and candidate selection rate of withdrawal: the annual liquid capacity divided by the oil reserves that stay mobile after the water breakthrough, 1/year Production · Field development concepts: surface facilities depreciation rate — the share of the remaining balance written off in a year, fraction Economics · Valuation methods: book value and market value how much NPV grows when X X X , US$ million per unit of X X X Economics · Geological and technical uncertainty of a project A A A heat production — the heat of radioactive decay released in 1 m³ of rock (usually quoted in µW/m³), W/m³ Geoscience · Structure and composition of the Earth heat production of the rock, µW/m³ Geoscience · Structure and composition of the Earth pre-exponential factor, same as for k k k Geoscience · Source rocks, maturation and migration area of the mature source rock (the kitchen), m² Geoscience · Source rocks, maturation and migration excess area of the horizon above its regional level, m² Geoscience · Practical structural geology area of the horizontal cross-section of the body, m² Geoscience · Geophysical exploration methods intercept: the reflection coefficient at normal incidence in the linear approximation, — Geoscience · Seismic waves, acoustic impedance and reflections area of the baffle across the flow: the length of the boundary times its height, m² Geoscience · Reservoir architecture and performance area bounded by the contour, m² Geoscience · Gross rock volume from maps area between the Lorenz curve and the diagonal, — Geoscience · Descriptive statistics in geology filtration area (of the wall), m² Logs and petrophysics · Borehole environment: invaded zone and mudcake mass number of the nucleus (its mass in units of the neutron mass), — Logs and petrophysics · Neutron log mass number of the nucleus, — Logs and petrophysics · Neutron log cross-sectional area of the sample, perpendicular to the current, m² Logs and petrophysics · Resistivity logs: electrical and induction tools coefficient of the formula, — Logs and petrophysics · Resistivity ratio methods and movable oil curvature parameter; for mixing by mass, the ratio of the densities, — Logs and petrophysics · Determining shale volume total mole fraction of hydrogen sulfide and carbon dioxide, y H 2 S + y C O 2 y_{\mathrm{H_2S}} + y_{\mathrm{CO_2}} y H 2 S + y C O 2 , fraction Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) a p / ( R T ) 2 a\,p/(RT)^2 a p / ( R T ) 2 , — Reservoir engineering · Cubic equations of state dimensionless parameter of the correlation, c o p c_o\,p c o p , — Reservoir engineering · Density and compressibility of reservoir oil factor decreasing from 1 at p = p sc p = p_{\text{sc}} p = p sc p = p k p = p_k p = p k , — Reservoir engineering · Equilibrium ratios: correlations and equations of state oil-bearing area, m² Reservoir engineering · Porosity area of the cross-section perpendicular to the flow, m² Reservoir engineering · Rock permeability area of the cross-section of the formation across the flow: thickness × width of the front, m² Reservoir engineering · Segregated flow and gravity displacement area of the drainage region, m² Well testing · Pseudo-steady-state flow and the shape factor constant of the regime, which depends on the properties of the reservoir and the well, Pa/sⁿ Well testing · Diagnosis with the pressure derivative amplitude of the redistribution pressure: by how much the separating of gas and liquid could raise the pressure over and above the inflow, Pa Well testing · Nonideal wellbore storage, well clean-up and changing skin amplitude: the value to which p ϕ p_\phi p ϕ , Pa Well testing · Nonideal wellbore storage, well clean-up and changing skin area of the cross-section in which the level rises (the annulus or the tubing), m² Well testing · Nonideal wellbore storage, well clean-up and changing skin area of the section: its length along the fault (the strike) times the thickness of the formation that is in contact across the fault, m² Well testing · Partially communicating faults anisotropy k h / k v k_h/k_v k h / k v , — Well testing · Comparing formation-tester, core and well-test data area of the oil–water contact under which the bottom water rises, m² Well testing · Two-phase flow and reservoir description from formation-tester data area of the common face of the cells, m² Simulation · What a reservoir simulation model is and why it is needed a constant of the given oil, mPa·s Simulation · Types of reservoir simulation model area of the block face perpendicular to the flow, m² Simulation · Permeability upscaling for single-phase flow cross-sectional area of the wall of the pipe body, mm² Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe area of the hole bottom, π D 2 / 4 \pi D^2/4 π D 2 /4 D D D , m² Drilling · Bit performance and cost per metre flow area of the choke, m² Drilling · Blowout prevention equipment filtering area, m² Drilling · Field testing of drilling fluids total flow area of the nozzles (TFA), m² Drilling · Circulating pressure losses total flow area of the nozzles, m² Drilling · Bit hydraulics optimisation departure, the distance from the wellhead to the projection of the point on the horizontal plane, m Drilling · Directional wells: applications and profile area of the bean orifice, π d 2 / 4 \pi d^2/4 π d 2 /4 , m² Production · Chokes, surface pressure losses and well temperature relaxation distance — the length over which the difference between the temperatures of the flow and of the rocks falls from its starting value by a factor of e e e , m Production · Chokes, surface pressure losses and well temperature relaxation distance, m Production · Chokes, surface pressure losses and well temperature poroelastic stress coefficient; the literature also uses a value half as large, η = A / 2 \eta = A/2 η = A /2 , — Production · Rock mechanics for hydraulic fracturing poroelastic stress coefficient, from 0 to 1, — Production · Rock mechanics for hydraulic fracturing filtration area: the end face of the core sample, m² (cm²) Production · Fracturing fluids and tip-screenout fracturing poroelastic stress coefficient; α \alpha α ν \nu ν , — Production · Sand production: types, prediction and cost of the problem area of the whole cross-section, π D 2 / 4 \pi D^2/4 π D 2 /4 , m² Production · Oil treating: separators, dehydration, desalting and stabilisation plan area of the tank (for a plate pack, the total horizontal projection of the plates), m² Production · Produced water: composition, treatment and disposal equal payment at the end of each year, US$ million per year Economics · Annuities and discounted production equal receipt (or payment) at the end of each year, US$ million per year Economics · Annuities and discounted production equal contribution at the end of each year, US$ million per year Economics · Annuities and discounted production equal yearly receipts at the end of each of the N N N , US$ million a year Economics · Cumulative cash flow and payback period equal capital charge at the end of each of n n n , US$ million a year Economics · Annual capital charge equal payment in each year of the set P P P , US$ million a year Economics · Annual capital charge annual capital charge in the years of production, US$ million a year Economics · Annual capital charge A 0 A_0 A 0 A 1 A_1 A 1 a 1 , a 2 a_1,\ a_2 a 1 , a 2 A f A_f A f a i j a_{ij} a ij A in A_{\text{in}} A in A k A_k A k a n a_n a n A s A_s A s A t A_t A t a , b a,\ b a , b constants fitted to the samples; b b b , — Geoscience · Reservoir quality: geological controls on porosity and permeability constants: in the original calibration of the model on Jurassic sandstones of the Norwegian shelf a = 1.98 ⋅ 10 − 22 a = 1.98\cdot 10^{-22} a = 1.98 ⋅ 1 0 − 22 b = 0.022 b = 0.022 b = 0.022 , mol/(cm²·s); °C⁻¹ Geoscience · Diagenesis: compaction, cementation and dissolution coefficients of the straight line fitted to the measurements in a well; b b b lg R o \lg R_o lg R o , —, 1/m Geoscience · Source rocks, maturation and migration constants of the detector, found by calibration; b b b , —; cm³/g Logs and petrophysics · Density log and photoelectric factor (Pe) coefficients found from core or cuttings of the same unit, % per g/t; % Logs and petrophysics · Lithology from the photoelectric factor and spectral gamma ray parameters of the substance at temperature T T T , MPa·m⁶/kmol², m³/kmol Reservoir engineering · Cubic equations of state multiplier and exponent; both are less than one and decrease with the solution gas–oil ratio, — Reservoir engineering · Oil viscosity and interfacial tension viscous and inertial flow resistance coefficients, by the formulas Well testing · Inflow at high rates: non-Darcy flow coefficients of the two-term equation, by the formula above Well testing · Inflow at high rates: non-Darcy flow concentrations of B a 2 + \mathrm{Ba^{2+}} B a 2 + S O 4 2 − \mathrm{SO_4^{2-}} S O 4 2 − , mol/L Production · Sources of formation damage a , m , n a,\ m,\ n a , m , n b b b bin size (distance between CMPs) in the dip direction, m Geoscience · Seismic acquisition and processing slope of the line — the ratio of accumulation rates in B and in A, — Geoscience · Well correlation width (thickness) of the baffle in the direction of flow, m Geoscience · Reservoir architecture and performance largest possible value, units of the parameter Geoscience · Probabilistic volumetrics by Monte Carlo simulation size of one data frame: all the transmitted curves of one sample, bit Logs and petrophysics · Open-hole logging: why, how and when exponent of the curve: 0 is exponential, 1 is harmonic decline, — Reservoir engineering · Reservoir engineering: tasks across the life of a field the volume of the molecules themselves in one kilomole, m³/kmol Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) co-volume — the volume of the molecules themselves in a kilomole of the substance, m³/kmol Reservoir engineering · Cubic equations of state slip coefficient, which depends on the gas and on the size of the channels, the same units of pressure Reservoir engineering · Rock permeability dimensionless difference between the average aquifer pressure and the pressure at the contact, in units of q w μ w / ( 2 π f k h ) q_w\mu_w/(2\pi fkh) q w μ w / ( 2 π f k h ) , — Reservoir engineering · Simplified water influx models: Fetkovich and Carter–Tracy drawdown per unit rate: 0.933 B μ k h ( ln 4 A γ C A r w 2 + 2 S ) 0.933\,\frac{B\mu}{kh}\left(\ln\frac{4A}{\gamma C_Ar_w^2} + 2S\right) 0.933 k h B μ ( ln γ C A r w 2 4 A + 2 S ) k k k μ \mu μ h h h 0.933 = 1 / ( 4 π ⋅ 0.0853 ) 0.933 = 1/(4\pi\cdot0.0853) 0.933 = 1/ ( 4 π ⋅ 0.0853 ) where the constants come from ), MPa/(m³/d) Well testing · Reservoir limit test thickness of the barrier (from the log), m Well testing · Pressure measurements in producing reservoirs: barriers and accuracy half-width of the band: the largest difference between the numbers of linked unknowns, — Simulation · Solving systems of linear equations in simulators length of the message: data plus service bits, bit Drilling · Measurement while drilling inertial resistance coefficient, MPa²/(thousand m³/d)² Production · Inflow performance relationship (IPR) how much NPV falls when Y Y Y , US$ million per unit of Y Y Y Economics · Geological and technical uncertainty of a project B B B gradient: the rate of change of R R R sin 2 θ \sin^2\theta sin 2 θ , — Geoscience · Seismic waves, acoustic impedance and reflections equivalent conductivity of the exchangeable cations, (S/m)/(meq/cm³) Logs and petrophysics · Water saturation in shaly sands mole fraction of hydrogen sulfide, fraction Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) mole fraction of hydrogen sulfide, y H 2 S y_{\mathrm{H_2S}} y H 2 S , fraction Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) b p / ( R T ) b\,p/(RT) b p / ( R T ) , — Reservoir engineering · Cubic equations of state formation volume factor of the fluid, m³/m³ Reservoir engineering · Flow regimes formation volume factor of the fluid (at the initial reservoir pressure), m³/m³ Reservoir engineering · Diffusivity equation fluid formation volume factor (reservoir volume per unit of volume at the surface); it appears in the oilfield forms, where the flow rate is at standard conditions, m³/m³ Well testing · Steady-state radial flow fluid formation volume factor, m³/m³ Well testing · Steady-state radial flow formation volume factor of the fluid, m³/m³ Well testing · Skin factor formation volume factor of the fluid (its volume in the reservoir per unit volume at standard conditions), m³/m³ Well testing · Well testing: purposes and types of test formation volume factor of the fluid (its volume in the reservoir per unit volume at the surface), m³/m³ Well testing · Wellbore storage oil formation volume factor, m³/m³ Well testing · Testing in a developed reservoir: Slider's method leakage factor k 2 h 2 b / k b \sqrt{k_2h_2b/k_b} k 2 h 2 b / k b , m Well testing · Pressure measurements in producing reservoirs: barriers and accuracy a constant of the given oil showing how steeply the viscosity falls with temperature, K Simulation · Types of reservoir simulation model bit diameter, inches Drilling · Abnormal formation pressures: origin, prediction and recognition total field from the magnetometers, nT Drilling · Survey instruments: magnetic, gyroscopic and inertial formation volume factor of the oil, m³/m³ Production · Inflow performance relationship (IPR) pressure rise from the inlet of the mixing chamber to the discharge, in fractions of the velocity head of the jet ρ v n 2 / 2 \rho v_{\text{n}}^2/2 ρ v n 2 /2 , — Production · Hydraulic pumps: piston and jet book value of the asset or group of assets, US$ million Economics · Valuation methods: book value and market value B 0 B_0 B 0 B g B_g B g volume of gas in the reservoir per unit of its volume at standard conditions, m³/m³ Reservoir engineering · Gas formation volume factor, compressibility and viscosity volume of the gas in the reservoir per unit of its volume at standard conditions, m³/m³ Reservoir engineering · Black oil model: solution gas–oil ratio and formation volume factors gas formation volume factor at the current average reservoir pressure p p p , m³/m³ Reservoir engineering · Material balance for gas reservoirs gas formation volume factor at the current pressure, m³/m³ Reservoir engineering · General material balance equation for oil reservoirs gas formation volume factor at intake conditions: B g = p sc p ⋅ T T sc Z B_g = \dfrac{p_{\text{sc}}}{p}\cdot\dfrac{T}{T_{\text{sc}}}\,Z B g = p p sc ⋅ T sc T Z , m³/m³ Production · Artificial lift: when it is needed and how to choose the method formation volume factor of the gas at the intake conditions: B g = p sc p ⋅ T T sc Z B_g = \dfrac{p_{\text{sc}}}{p}\cdot\dfrac{T}{T_{\text{sc}}}\,Z B g = p p sc ⋅ T sc T Z , m³/m³ Production · Electric submersible pumps (ESP) B g i B_{gi} B g i B o B_o B o B o , B w B_o,\ B_w B o , B w B o , B w , B g B_o,\ B_w,\ B_g B o , B w , B g B o i B_{oi} B o i B t B_t B t B w B_w B w B , μ B,\ \mu B , μ c c c mass of mineral that 1 kg of sea water can yield: NaCl — about 0.0274, CaSO₄ — about 0.0014, kg/kg Geoscience · Sedimentary rocks and their classification exponent, — Geoscience · Faults value of the contour that lies between z a z_a z a z b z_b z b , m Geoscience · Structure maps and contouring volume of cake formed per unit volume of filtrate, — Logs and petrophysics · Borehole environment: invaded zone and mudcake the ratio R x o / R t R_{xo}/R_t R x o / R t , — Logs and petrophysics · Interpretation charts: how to read them translation of the phase — the average over its composition, m³/kmol Reservoir engineering · Cubic equations of state compaction coefficient. It is fitted to the data of a particular basin, and it is larger for clays than for sands, km⁻¹ Reservoir engineering · Porosity compressibility, 1/MPa Reservoir engineering · Rock compressibility and the effect of stress on core properties compressibility of the mobile fluid, 1/Pa Reservoir engineering · Diffusivity equation 1 for spherical flow (an interval in the middle of the reservoir), 2 for hemispherical flow (an interval at the top or bottom), — Well testing · Partial penetration and well deviation compaction coefficient of the given shale, MPa⁻¹ Drilling · Abnormal formation pressures: origin, prediction and recognition speed of the longitudinal wave along the pipe (the speed of sound along it, as in a rod), E / ρ steel \sqrt{E/\rho_{\text{steel}}} E / ρ steel , m/s Drilling · Casing design volume of cake formed per unit volume of filtrate, — Drilling · Field testing of drilling fluids concentration of clay per 1 m³ of suspension, kg/m³ Drilling · Water-based muds and clay chemistry the coefficient of the loss law Δ p sys = c Q m \Delta p_{\text{sys}} = cQ^m Δ p sys = c Q m Δ p sys 1 / Q 1 m \Delta p_{\text{sys}1}/Q_1^m Δ p sys 1 / Q 1 m , depends on m m m Drilling · Bit hydraulics optimisation speed of the pulse in the mud inside the pipe, m/s Drilling · Measurement while drilling speed of the pulse, m/s Drilling · Measurement while drilling constant of the devices, reduced to a metre of wellbore, Pa·s²/m⁴ Production · Horizontal wells mass concentration of the component at standard conditions, g/m³ Production · Gas processing and compression levelised technical cost per barrel, $/bbl Economics · Unit costs per barrel the cost recovery limit: the largest share of the year's revenue that can go to recover costs, fraction Economics · Licences and contracts for subsoil use value to society of a tonne of CO₂ avoided: an estimate, not a payment set by law, US$/t Economics · State regulation of field development cost recovery limit: the largest share of revenue after royalty that can go to cost oil, fraction Economics · Petroleum fiscal systems and taxation the stake: the cost to the company of one well, US$ million Economics · Risk reduction and diversification Δ p c \Delta p_c Δ p c C C C uniformity coefficient; D p D_p D p p p p , — Geoscience · Sediment texture: grain size, sorting and shape intergranular cement: quartz, carbonates, authigenic clay minerals, % Geoscience · Reservoir quality: geological controls on porosity and permeability intergranular cement, % of the present volume Geoscience · Reservoir quality: geological controls on porosity and permeability fraction of the quartz surface covered by coats on the grains, — Geoscience · Diagenesis: compaction, cementation and dissolution constant that depends on the greatest burial depth: 0.5 for less than 3 km; 0.25 for 3 to 3.5 km; 0 for more than 3.5 km, — Geoscience · Faults strength of the “pole”, nT·m² Geoscience · Geophysical exploration methods share of the reservoir in the largest connected body, fraction Geoscience · Reservoir architecture and performance partial sill: the variability that is related to distance, units² Geoscience · Spatial correlation and the variogram value of the reserves of the commercial categories A, B and C1 approved by the state reserves commission, tenge Geoscience · Classification of reserves and resources calibration constant, % Logs and petrophysics · Nuclear magnetic resonance (NMR) logging electrical conductivity, S/m Logs and petrophysics · Resistivity logs: electrical and induction tools empirical constant: from 0.625 to 0.7 for different authors; later comparisons point to 0.67, and old charts use 0.7, — Logs and petrophysics · Porosity from the sonic log Larionov coefficient, which sets the curvature: 3.7 for Tertiary (Paleogene and Neogene) unconsolidated rocks (loose, poorly cemented), 2 for older consolidated rocks (well cemented), — Logs and petrophysics · Determining shale volume Larionov coefficient, — Logs and petrophysics · Determining shale volume constant of the pressure anomaly (the departure from normal pressure) for a hydrodynamically connected system, Pa Reservoir engineering · Reservoir pressure and temperature number of components, — Reservoir engineering · Phase behaviour: pure substances and binary mixtures parameter of the aquifer model: the slope of the line, depend on the model Reservoir engineering · Straight-line material balance (Havlena–Odeh method) wellbore storage coefficient: the volume of fluid that the wellbore gives out or takes in when the bottomhole pressure changes by one unit, m³/Pa Well testing · Wellbore storage wellbore storage coefficient, m³/Pa Well testing · Wellbore storage wellbore storage coefficient from the time match, m³/MPa Well testing · Type-curve matching wellbore storage coefficient at the depth of the gauge, m³/Pa Well testing · Nonideal wellbore storage, well clean-up and changing skin wellbore storage coefficient after the redistribution is over, m³/Pa Well testing · Nonideal wellbore storage, well clean-up and changing skin coefficient after the redistribution, m³/MPa Well testing · Nonideal wellbore storage, well clean-up and changing skin flow shape factor: 0.5 for flow to a sphere surrounded by rock on all sides, 1 for flow to a hemisphere at an impermeable plane; for a probe on the wall of a borehole of usual diameter, about 0.67, — Well testing · Pressure measurement with the wireline formation tester storage capacity of the block, c t V p c_tV_p c t V p , m³/MPa Well testing · Lumped multi-tank material balance model Courant number: the fraction of a cell that the front crosses in a step, — Simulation · Grids in reservoir simulation models Land coefficient: the larger it is, the less is trapped, — Simulation · Petrophysical input for simulation: relative permeability and capillary pressure cost of the well according to the estimate, US$ thousand Drilling · Drilling time and cost excess weight of the drill collars and heavy-weight pipe in mud over the weight of drill pipe of the same length, kN Drilling · Drilling rig: power and hoisting systems slope of the line on a plot of volume against the square root of time, cm³/min1 / 2 ^{1/2} 1/2 1 / 2 ^{1/2} 1/2 Drilling · Field testing of drilling fluids a coefficient reflecting the properties of the reservoir and the fluid; its dimension depends on n n n , m³/(d·MPa²ⁿ) Production · Inflow performance relationship (IPR) a coefficient depending on the properties of the reservoir and the gas, thousand m³/(d·MPa²ⁿ) Production · Inflow performance relationship (IPR) counterbalance effect: the force of the counterweights, converted into a force at the polished rod, N Production · Sucker-rod pumping total costs: the cost of the job plus the value of the production not received during the job, US$ Production · Acid treatments: principle, economics and candidate selection mass fraction of acid in the solution, fraction Production · Acid systems and treatment design uniformity coefficient , — Production · Sand control methods equilibrium concentration of dissolved oxygen, mg/L Production · Water injection systems the investment, assigned to the moment one year before the first payment, US$ million Economics · Annual capital charge the investment at the start of the service life, US$ million Economics · Annual capital charge the investment, US$ million Economics · Annual capital charge the investment, assigned to the moment one year before the first year of service, US$ million Economics · Annual capital charge cost of the exploration well, spent whatever the outcome, US$ million Economics · Expected monetary value and preference theory cost of the well, US$ million Economics · Decision trees and the value of information C 0 C_0 C 0 C a C_a C a C d C_d C d discharge coefficient, which depends on the shape of the restriction (usually 0.6–0.95), — Drilling · Blowout prevention equipment discharge coefficient, — Drilling · Circulating pressure losses discharge coefficient of the nozzles, about 0.95, — Drilling · Bit hydraulics optimisation discharge coefficient of the choke, — Production · Chokes, surface pressure losses and well temperature discharge coefficient: allows for the contraction of the jet and for friction, — Production · Chokes, surface pressure losses and well temperature discharge coefficient: about 0.6 for new holes with sharp edges, and it grows to about 0.9 when proppant rounds the edges, — Production · Perforating operations: gun conveyance and procedures C D C_D C D c e c_e c e c f c_f c f c j c_j c j C j C_j C j C p C_p C p c t c_t c t total compressibility of the rocks and fluids of the compartment, 1/Pa Geoscience · Reservoir architecture and performance total compressibility, per unit of pore volume, 1/MPa Reservoir engineering · Flow regimes total compressibility, 1/Pa Reservoir engineering · Flow regimes total compressibility of the aquifer, c w + c f c_w + c_f c w + c f , 1/Pa Reservoir engineering · Aquifer models: water influx total compressibility of rock and fluids, S o c o + S w c w + c f S_oc_o + S_wc_w + c_f S o c o + S w c w + c f Flow regimes ), 1/MPa Reservoir engineering · Why water is injected: pressure maintenance and oil displacement total compressibility of the rocks and fluids (how much their volume changes when the pressure changes), 1/Pa Well testing · Pseudo-steady-state flow and the shape factor total compressibility of rock and fluids, 1/MPa Well testing · Well testing: purposes and types of test total compressibility, 1/MPa Well testing · Pressure drawdown analysis total compressibility of the reservoir and the fluids, 1/MPa Well testing · Pressure build-up analysis total compressibility of the reservoir and the fluids in it, 1/MPa Well testing · Wellbore storage total compressibility of the rocks and fluids, 1/Pa Well testing · Reservoir limit test total compressibility of the rock and the fluids, 1/MPa Well testing · Pressure measurements in producing reservoirs: barriers and accuracy total compressibility of oil, connate water and rock together (how much their volume changes when the pressure changes), MPa⁻¹ Simulation · What a reservoir simulation model is and why it is needed total compressibility: compressibility of the fluid c c c c f c_f c f , 1/Pa Simulation · Pressure equation for single-phase flow total compressibility, 1/MPa Simulation · Pressure equation for single-phase flow total compressibility of the reservoir fluid and the pores, 1/Pa Production · Fracturing fluids and tip-screenout fracturing C v C_v C v C w C_w C w C a C O 3 \mathrm{CaCO_3} CaC O 3 C a M g ( C O 3 ) 2 \mathrm{CaMg(CO_3)_2} CaMg ( C O 3 ) 2 d d d grain diameter, mm Geoscience · Sediment texture: grain size, sorting and shape particle diameter, m Geoscience · Sediment texture: grain size, sorting and shape borehole diameter from the caliper log, m Geoscience · Primary sedimentary structures horizontal distance from the CMP to the reflection point, up-dip, m Geoscience · Seismic acquisition and processing distance between the wells, m Geoscience · Well correlation inner diameter of the capillary, m Reservoir engineering · Laboratory PVT tests diameter of the grains, m Reservoir engineering · Rock permeability distance from the well to the apex of the angle, m Well testing · Several boundaries: parallel faults and wedge-shaped blocks liner diameter, m Drilling · Rig circulating and rotary systems inside diameter (nominal), m Drilling · Casing: purpose, types, properties and standards particle diameter, m Drilling · Solids control in drilling fluids inside diameter of the pipe; in the annulus, the outside diameter of the pipes, m Drilling · Drilling fluid rheology and flow regimes inside diameter of the pipe, m Drilling · Circulating pressure losses inside diameter of the pipe; in the annulus, the hydraulic diameter D − d D - d D − d , m Drilling · Circulating pressure losses diameter of the pipe; for the annulus, approximately the hydraulic diameter, m Drilling · Circulating pressure losses inner diameter of the drill pipe, m Drilling · Measurement while drilling inner diameter of the tubing, m Production · Nodal analysis of the production system inner diameter of the pipe, m Production · Multiphase flow in tubing tunnel diameter, m Production · Effect of completion on inflow diameter of the cross-section of the rotor, equal to the width of the slot of the stator, m Production · Progressing cavity pumps and hybrid systems diameter of the grain, m Production · Fracturing fluids and tip-screenout fracturing share of the recoverable reserves produced per year on the plateau, % per year Production · Field development concepts: surface facilities droplet diameter, m Production · Oil treating: separators, dehydration, desalting and stabilisation diameter of the droplet, m Production · Produced water: composition, treatment and disposal rate of natural decline of production, fraction per year Economics · Oil companies and investment delay of first oil, years Economics · Sensitivity analysis and scenarios D D D flexural rigidity of the plate, N·m Geoscience · Plate tectonics and sedimentary basins grain size, cm Geoscience · Diagenesis: compaction, cementation and dissolution slip on the fault plane (net slip), m Geoscience · Faults self-diffusion coefficient of the fluid, m²/s Logs and petrophysics · Nuclear magnetic resonance (NMR) logging nominal decline rate, 1/year Reservoir engineering · Reservoir engineering: tasks across the life of a field depth, counted downward; ∇ D \nabla D ∇ D , m Reservoir engineering · Diffusivity equation non-Darcy coefficient: the coefficient of the inertial skin, s/m³ Well testing · Inflow at high rates: non-Darcy flow non-Darcy coefficient per unit of gas rate at standard conditions, s/m³ Well testing · Inflow at high rates: non-Darcy flow depth (length of the string along the hole), m Drilling · Drilling rig: power and hoisting systems outside diameter of the pipe body, m Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe outside diameter, m Drilling · Casing: purpose, types, properties and standards outside diameter of the pipe, m Drilling · Casing design change of the amplitude of the ringing over one round trip across the wall and back, dB Drilling · Remedial cementing, cement plugs and cement evaluation bit diameter, m Drilling · Solids control in drilling fluids diameter of the hole, or inside diameter of the casing, m Drilling · Drilling fluid rheology and flow regimes distance between the centres of the two arcs, m Drilling · Directional wells: applications and profile distance between the centres of the wells at the points considered, m Drilling · Survey instruments: magnetic, gyroscopic and inertial outer diameter of the conductor, m Drilling · Offshore and subsea drilling plunger diameter, m Production · Sucker-rod pumping diameter of the gravel grains, mm Production · Sand control methods inner diameter of the vessel, m Production · Oil treating: separators, dehydration, desalting and stabilisation debt: loans, bonds and similar obligations, US$ million Economics · Valuation methods: book value and market value nominal decline rate (the exponent in q = q i e − D t q = q_i e^{-Dt} q = q i e − D t d = 1 − e − D d = 1 - e^{-D} d = 1 − e − D , 1/year Economics · Annuities and discounted production market value of debt, US$ million Economics · Choosing the discount rate the nominal decline rate of the production rate, 1/year Economics · Annual capital charge the result of the data, for example the measured rock volume, — Economics · Geological and technical uncertainty of a project d i d_i d i distance from the point ( x , y ) (x, y) ( x , y ) i i i , m Geoscience · Structure maps and contouring diameter of the invaded zone (step model), m Logs and petrophysics · Borehole environment: invaded zone and mudcake diameter of the invaded zone, m Logs and petrophysics · Resistivity logs: electrical and induction tools decimal logarithm of their ratio: 0 means agreement, 0.301 means twice as large, −0.301 means half as large, — Well testing · Comparing formation-tester, core and well-test data outside diameter of the drill pipe or drill collars in that interval, m Drilling · How a well is drilled: the process and the people involved diameters of the nozzles, m Drilling · Circulating pressure losses D i D_i D i d j d_j d j d s d_s d s D , d D,\ d D , d outside diameter and bore diameter, m Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe outside and inside diameters of the pipe body, mm Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe outside and inside diameters, mm Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe diameter of the hole (inside diameter of the casing) and outside diameter of the pipes, m Drilling · Drilling fluid rheology and flow regimes outside and inside diameters of the ring, m Drilling · Circulating pressure losses outer diameter of the sample and diameter of the hole, mm Production · Sand production: types, prediction and cost of the problem e e e relative elongation of a line (extension); a negative value is shortening, — Geoscience · Stress, strain and structural analysis relative elongation along the layer (strain ); positive for extension, negative for shortening, — Geoscience · Folds, salt diapirs and their relationship to faults displacement of the tool from the axis of the casing, m Drilling · Remedial cementing, cement plugs and cement evaluation elementary charge, 1.602 ⋅ 10 − 19 1.602\cdot10^{-19} 1.602 ⋅ 1 0 − 19 , C Drilling · Water-based muds and clay chemistry eccentricity: the offset of the axis of the rotor from the axis of the stator, m Production · Progressing cavity pumps and hybrid systems depth of embedment of the grains into each wall, m Production · Fracture design: size and conductivity nominal escalation rate of the price, fraction per year Economics · Inflation: nominal and real money the rate of the rent tax, or the rate of the tier of the excess profit tax into which the increase falls, fraction Economics · Petroleum fiscal systems and taxation the rent tax rate, fraction Economics · Petroleum fiscal systems and taxation E E E Young's modulus of the lithosphere; typically 70 GPa, Pa Geoscience · Plate tectonics and sedimentary basins activation energy (the energy barrier that molecules must overcome to react); for the breakdown of kerogen it is usually 200–250 kJ/mol, J/mol Geoscience · Source rocks, maturation and migration activation energy, J/mol Geoscience · Source rocks, maturation and migration elevation of the station (height above sea level), m Geoscience · Seismic acquisition and processing energy of the neutron before the collision, eV Logs and petrophysics · Neutron log Young's modulus of steel, 2.07 ⋅ 10 11 2.07\cdot10^{11} 2.07 ⋅ 1 0 11 , Pa Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe Young's modulus of steel (its stiffness), 2.07 ⋅ 10 11 2.07\cdot10^{11} 2.07 ⋅ 1 0 11 , Pa Drilling · Drill string design modulus of elasticity of steel, 207,000 MPa, Pa Drilling · Bit performance and cost per metre Young's modulus of steel, about 207,000 MPa, Pa Drilling · Casing design cleaning efficiency : the share of drilled rock that the equipment removes, — Drilling · Solids control in drilling fluids Young's modulus of steel, Pa Drilling · Measurement while drilling Young's modulus of steel (how stiff it is), 207,000, MPa Production · Completion string equipment Young's modulus of steel (how stiff it is), 207,000 MPa = 2.07·10¹¹ Pa, Pa Production · Wireline operations Young's modulus of steel (a measure of how stiff it is), about 207,000 MPa, Pa Production · Sucker-rod pumping Young's modulus of steel, Pa Production · Sucker-rod pumping static Young's modulus of the layer, MPa Production · Rock mechanics for hydraulic fracturing mixing efficiency: the share of the wash water that really meets the droplets of produced water, from 0 to 1 Production · Oil treating: separators, dehydration, desalting and stabilisation market value of equity — market capitalisation: the share price multiplied by the number of shares, US$ million Economics · Valuation methods: book value and market value market value of equity (market capitalisation: what the shares of the company are worth on the stock market), US$ million Economics · Choosing the discount rate E 0 E_0 E 0 E 1 E_1 E 1 E k E_k E k E R E_R E R E t E_t E t E x E_x E x f f f fraction of the rock volume occupied by detrital quartz grains, — Geoscience · Diagenesis: compaction, cementation and dissolution frequency of oscillation, Hz Geoscience · Seismic waves, acoustic impedance and reflections frequency, Hz Geoscience · Seismic waves, acoustic impedance and reflections dominant frequency of the reflection, Hz Geoscience · Seismic acquisition and processing Larmor frequency, the resonance frequency of protons, MHz Logs and petrophysics · Nuclear magnetic resonance (NMR) logging fraction of the second mineral in the matrix volume, fraction Logs and petrophysics · Lithology and porosity from crossplots fraction of the perimeter of the accumulation that the aquifer touches, θ / 360 ° \theta/360° θ /360° , — Reservoir engineering · Aquifer models: water influx fraction of the perimeter of the accumulation that the aquifer touches, — Reservoir engineering · Aquifer models: water influx frequency of the signal, Hz Drilling · Remedial cementing, cement plugs and cement evaluation Fanning friction factor, f = 2 τ w / ( ρ v 2 ) f = 2\tau_w/(\rho v^2) f = 2 τ w / ( ρ v 2 ) , — Drilling · Circulating pressure losses Fanning friction factor, — Drilling · Circulating pressure losses share of the interval drilled in sliding, — Drilling · Deflection tools and downhole motors dimensionless time function of heat conduction in the rocks, — Production · Chokes, surface pressure losses and well temperature annual rate of inflation (a fraction), — Economics · Project cash flow annual rate of price growth — general inflation or sector-specific escalation, fraction per year Economics · Interest and compounding rate of inflation — the growth of the general price level, fraction per year Economics · Interest and compounding constant yearly inflation rate, fraction per year Economics · Inflation: nominal and real money inflation rate, fraction per year Economics · Inflation: nominal and real money general inflation, fraction per year Economics · Inflation: nominal and real money false-alarm rate P ( + ∣ H ˉ ) P(+\mid \bar H) P ( + ∣ H ˉ ) , fraction Economics · Decision trees and the value of information the dependence of NPV on this parameter, other things equal, US$ million Economics · Geological and technical uncertainty of a project F F F fold axes and the strike of thrusts, — Geoscience · Structural styles and tectonic history Faraday constant, 96,485 C/mol, C/mol Logs and petrophysics · Spontaneous potential (SP) log formation resistivity factor, — Logs and petrophysics · Microresistivity tools and flushed-zone resistivity formation resistivity factor, F = a / ϕ m F = a/\phi^m F = a / ϕ m , — Logs and petrophysics · Determining formation water resistivity number of degrees of freedom — independent intensive parameters (pressure, temperature, phase compositions), — Reservoir engineering · Phase behaviour: pure substances and binary mixtures volume of the oil, gas and water produced, converted to reservoir conditions at pressure p p p , m³ Reservoir engineering · General material balance equation for oil reservoirs underground withdrawal of oil, gas and water, m³ Reservoir engineering · General material balance equation for oil reservoirs underground withdrawal, m³ Reservoir engineering · Straight-line material balance (Havlena–Odeh method) underground withdrawal accumulated to date, N p [ B o + ( R p − R s ) B g ] + W p B w N_p[B_o + (R_p - R_s)B_g] + W_pB_w N p [ B o + ( R p − R s ) B g ] + W p B w R p R_p R p , m³ Reservoir engineering · Why water is injected: pressure maintenance and oil displacement dimensionless critical rate (an approximation fitted to calculations), — Well testing · Water and gas coning multiplier of the transmissibility between the cells on opposite sides of the fault, from 0 to 1, — Well testing · Partially communicating faults the systematic multiplier that we need to notice (for example 1.5), — Well testing · Comparing formation-tester, core and well-test data multiplier of the transmissibility of the connection without the fault, from 0 to 1, — Simulation · Interblock flow and transmissibility tensile load in the given section, MN Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe effective axial force, N Drilling · Drill string design the force with which the jets press on the bottom, that is, the momentum that they bring in a second, N Drilling · Bit hydraulics optimisation jet impact force, F = C d Q 2 ρ Δ p b F = C_dQ\sqrt{2\rho\,\Delta p_{\text{b}}} F = C d Q 2 ρ Δ p b , N Drilling · Bit hydraulics optimisation side force with which the bit presses on the low side of the hole, N Drilling · Deflection tools and downhole motors friction losses in the unit, expressed as an extra pressure drop of the power fluid, MPa Production · Hydraulic pumps: piston and jet factor by which the treatment raises productivity, — Production · Acid treatments: principle, economics and candidate selection fixed costs per year, US$ million Economics · Cash flow model of an oil and gas project fixed costs of the year that can be avoided by stopping production, US$ million Economics · Cash flow model of an oil and gas project f 1 f_1 f 1 f i f_i f i f w f_w f w share of water in the total flow at reservoir conditions, — Reservoir engineering · Relative permeability fractional flow of water, — Reservoir engineering · Buckley–Leverett theory and the Welge method share of water in the reservoir flow rate through the cross-section, — Reservoir engineering · Segregated flow and gravity displacement water fraction in the flow, — Well testing · Water and gas coning share of water in the total mobility, — Well testing · Two-phase flow and reservoir description from formation-tester data fractional flow of water: its share of the total flow if gravity and capillary pressure are ignored, — Simulation · Two-phase flow equations fractional flow of water λ w / λ t \lambda_w/\lambda_t λ w / λ t , — Simulation · IMPES and fully implicit schemes share of water in the mud, from the retort, fraction Drilling · Field testing of drilling fluids share of water from the retort, fraction Drilling · Field testing of drilling fluids share of water in the mud from the retort, — Drilling · Solids control in drilling fluids Δ p fr \Delta p_{\text{fr}} Δ p fr g g g acceleration due to gravity, 9.81, m/s² Geoscience · Plate tectonics and sedimentary basins gravitational acceleration, 9.81, m/s² Geoscience · Primary sedimentary structures acceleration of gravity, 9.81, m/s² Geoscience · Reservoir and seal observed gravity, corrected for tides and instrument drift, mGal Geoscience · Geophysical exploration methods acceleration due to gravity, 9.81 m/s², m/s² Reservoir engineering · Reservoir pressure and temperature acceleration due to gravity, m/s² Reservoir engineering · Reservoir pressure and temperature acceleration due to gravity, 9.81, m/s² Reservoir engineering · Density and compressibility of reservoir oil acceleration of gravity, 9.81, m/s² Reservoir engineering · Fractional flow function and mobility ratio acceleration of gravity, m/s² Reservoir engineering · Displacement in heterogeneous reservoirs acceleration due to gravity, 9.81, m/s² Well testing · Well inflow: the well performance diagram acceleration of gravity, 9.81, m/s² Well testing · Nonideal wellbore storage, well clean-up and changing skin hydrostatic constant: 0.00981 0.00981 0.00981 , MPa·cm³/(g·m) Simulation · Building a simulation model: input data and results acceleration due to gravity, 9.81, m/s² Drilling · Drill string design acceleration due to gravity, standard value 9.80665 m/s², m/s² Drilling · Pore pressure and overburden pressure acceleration due to gravity, m/s² Drilling · Pore pressure and overburden pressure acceleration due to gravity, 9.81 m/s², m/s² Drilling · Casing design acceleration of gravity, 9.81, m/s² Drilling · Deflection tools and downhole motors acceleration due to gravity, m/s² Production · Well completion: opening the reservoir and the tubing string acceleration due to gravity, 9.81 m/s², m/s² Production · Nodal analysis of the production system acceleration of free fall, 9.81 m/s², m/s² Production · Sucker-rod pumping acceleration of free fall, m/s² Production · Electric submersible pumps (ESP) acceleration due to gravity, 9.81 m/s². The product ρ kill g H \rho_{\text{kill}} g H ρ kill g H , m/s² Production · Unloading a gas lift well: valves and mandrels acceleration of gravity, m/s² Production · Acid systems and treatment design acceleration of gravity, 9.81, m/s² Production · Sand production: types, prediction and cost of the problem acceleration due to gravity, 9.81, m/s² Production · Oil treating: separators, dehydration, desalting and stabilisation acceleration due to gravity, 9.81 m/s²; in a hydrocyclone and a centrifuge the centrifugal acceleration takes its place, m/s² Production · Produced water: composition, treatment and disposal constant growth rate of the flow, g < i g < i g < i , fraction per year Economics · Valuation methods: book value and market value return on the investment: the annual rate at which the invested money grows, fraction per year Economics · Discounting and present value annual rate of change of the payment; for a decline it is negative: g = − d g = -d g = − d , fraction per year Economics · Annuities and discounted production the gain of a discovery in stakes, — Economics · Risk reduction and diversification G G G shear modulus: resistance to a change of shape, Pa Geoscience · Structure and composition of the Earth gravitational constant, 6.6743 ⋅ 10 − 11 6.6743\cdot10^{-11} 6.6743 ⋅ 1 0 − 11 , m³/(kg·s²) Geoscience · Geophysical exploration methods gravitational constant, m³/(kg·s²) Geoscience · Geophysical exploration methods free gas initially in place at standard conditions (GIIP ), m³ Geoscience · Volumetric estimation of hydrocarbons in place geometric factor of the invaded zone: its share in the signal, — Logs and petrophysics · Borehole environment: invaded zone and mudcake shear modulus: the resistance to a change of shape, Pa Logs and petrophysics · Sonic log dynamic shear modulus, Pa Logs and petrophysics · Sonic log gradient of the magnetic field in the sensitive zone (how fast the field changes with distance; 1 T/m = 100 G/cm), T/m Logs and petrophysics · Nuclear magnetic resonance (NMR) logging gas initially in place at standard conditions (GIIP ), m³ Reservoir engineering · Material balance for gas reservoirs initial volume of the gas of the cap at standard conditions, G = m N B o i / B g i G = mNB_{oi}/B_{gi} G = m N B o i / B g i , sm³ Reservoir engineering · General material balance equation for oil reservoirs mass flux: the mass flow rate of gas divided by the cross-sectional area of the sample, kg/(m²·s) Well testing · Inflow at high rates: non-Darcy flow pressure gradient of the fluid in the formation, Pa/m Well testing · Pressure measurement with the wireline formation tester pressure gradient: the slope of the line, Pa/m Well testing · Pressure measurement with the wireline formation tester gradient without capillary pressure, the formula of the section on the two-phase gradient, Pa/m Well testing · Two-phase flow and reservoir description from formation-tester data magnitude of the average gradient in the calculation where the pressure falls along x x x , Pa/m Simulation · Permeability upscaling for single-phase flow weight on bit, N Drilling · Drill string design amount of gas in the mud: the volume at standard conditions (gas measured at surface pressure and temperature) per 1 m³ of mud, m³/m³ Drilling · Oil-based muds separation factor: how many times the centrifugal acceleration is greater than g g g , — Drilling · Solids control in drilling fluids total gravity from the accelerometers, G x 2 + G y 2 + G z 2 \sqrt{G_x^2 + G_y^2 + G_z^2} G x 2 + G y 2 + G z 2 , g Drilling · Survey instruments: magnetic, gyroscopic and inertial total gravity from the accelerometers, g Drilling · Survey instruments: magnetic, gyroscopic and inertial shear modulus of steel (its resistance to twisting), about 8 ⋅ 10 10 8\cdot 10^{10} 8 ⋅ 1 0 10 , Pa Production · Progressing cavity pumps and hybrid systems Nolte's function: the dimensionless time of the pressure decline, — Production · Rock mechanics for hydraulic fracturing payments to the state over the whole life of the project, US$ million Economics · Petroleum fiscal systems and taxation G m G_m G m G o G_o G o G T G_T G T G w G_w G w G R GR GR h h h height of the mountains above the surface of that plain, km Geoscience · Structure and composition of the Earth thickness of the upper layer (the crust), km Geoscience · Structure and composition of the Earth thickness of the mineral layer without pores, m Geoscience · Sedimentary rocks and their classification flow depth, m Geoscience · Primary sedimentary structures peak-to-trough height of the sinusoid — the difference between the depths of its lowest and highest points, m Geoscience · Primary sedimentary structures channel depth at bankfull level; in an ancient section, the thickness of a complete channel cycle, m Geoscience · Continental environments: aeolian and fluvial height above the free water level, m Geoscience · Reservoir and seal effective thickness of the source rock, m Geoscience · Source rocks, maturation and migration head of the formation water — the elevation of the potentiometric surface, m Geoscience · Traps and timing true (stratigraphic) thickness — measured along the normal to the bedding, m Geoscience · Stress, strain and structural analysis true thickness of the bed, m Geoscience · Stress, strain and structural analysis thickness of a layer that bends as a whole (no slip within it), m Geoscience · Folds, salt diapirs and their relationship to faults thickness of the competent layer, m Geoscience · Folds, salt diapirs and their relationship to faults size of the fracture in its plane, across the flow, m Geoscience · Fractures and naturally fractured reservoirs elevation of the station above the reference level (usually above sea level), m Geoscience · Geophysical exploration methods true thickness (isopach), at right angles to the bedding, m Geoscience · Cross-sections from maps, map combination and faults on maps lag: the distance (and, over an area, the direction) between the points of a pair, m Geoscience · Spatial correlation and the variogram lag, h > 0 h > 0 h > 0 h = 0 h = 0 h = 0 , m Geoscience · Spatial correlation and the variogram bed thickness, m Logs and petrophysics · Open-hole logging: why, how and when thickness of the bed into which this volume has gone, m Logs and petrophysics · Borehole environment: invaded zone and mudcake average net oil-saturated thickness, m Reservoir engineering · Porosity height above the free water level, m Reservoir engineering · Fluid saturation thickness of the sample along the beam, cm Reservoir engineering · Core analysis net thickness of the reservoir, m Reservoir engineering · Rock permeability thickness of the reservoir over which the pressure has fallen, m Reservoir engineering · Rock compressibility and the effect of stress on core properties height of the meniscus above the level where the pressures of the two fluids are equal, m Reservoir engineering · Capillary pressure and the transition zone net reservoir thickness (only the layers that can flow), m Well testing · Steady-state radial flow oil-saturated thickness above the OWC, m Well testing · Water and gas coning current oil-saturated thickness, m Well testing · Water and gas coning net thickness of the reservoir, m Well testing · Wellbore storage thickness of the tight unit, m Well testing · Pressure measurements in producing reservoirs: barriers and accuracy thickness of the layer of rings, m Simulation · Interblock flow and transmissibility thickness of the reservoir that takes the water, m Simulation · Special topics in upscaling worn height of the cutter: how far the wear flat has cut into the cutter across its diameter; measured across the diamond layer, mm Drilling · Bit selection and dull grading fraction of the cutting structure that is worn: 0 is new, 1 is completely worn, — Drilling · Bit performance and cost per metre vertical height of the column — the true vertical depth below the top of the column, m Drilling · Pore pressure and overburden pressure true vertical depth from the chosen datum, m Drilling · Pore pressure and overburden pressure true vertical depth of that formation below the rotary table, m Drilling · Pore pressure and overburden pressure true vertical depth of the formation that has kicked; with the bit on the bottom, the depth of the bottom, m Drilling · Well kill methods true vertical depth of the formation that has kicked, m Drilling · Well kill methods vertical depth of the formation, m Drilling · Blowout prevention equipment vertical depth of the reservoir (measured straight down), m Production · Well completion: opening the reservoir and the tubing string net thickness of the reservoir, m Production · Inflow performance relationship (IPR) distance between shots in the vertical direction, m Production · Effect of completion on inflow head of the stage at the rate q in q_{\text{in}} q in , m Production · Electric submersible pumps (ESP) reservoir thickness, m Production · Formation damage and damage skin thickness of the reservoir between the barriers, m Production · Rock mechanics for hydraulic fracturing level of the liquid (or of the interface) above the bottom, m Production · Oil treating: separators, dehydration, desalting and stabilisation H H H height of the column of evaporated sea water, m Geoscience · Sedimentary rocks and their classification flow depth, m Geoscience · Primary sedimentary structures heating rate of the rock, °C/s Geoscience · Diagenesis: compaction, cementation and dissolution thickness of the coastal wedge — from the toe of the shoreface to the top of the beach and ridges, m Geoscience · Coastal, shallow-marine and deep-marine environments how far below the point the free water level of the accumulation can fall before the fault at this point starts to let hydrocarbons through, m Geoscience · Faults height of the accumulation, from the crest to the contact, m Geoscience · Gross rock volume from maps the thickness of the layer that the hydrocarbons would form if we gathered them out of the pores into a solid layer; the volume of hydrocarbons at reservoir conditions per unit area, m Geoscience · Volumetric estimation of hydrocarbons in place hydrocarbon pore thickness of the bed, h ϕ e ( 1 − S w ) h\,\phi_e\,(1 - S_w) h ϕ e ( 1 − S w ) , m Logs and petrophysics · Log interpretation workflow true vertical depth of the bottom (the middle of the reservoir), m Reservoir engineering · Reservoir pressure and temperature thickness of the unit, m Reservoir engineering · Reservoir heterogeneity and permeability averaging reservoir volume of the oil and gas produced, m³ Reservoir engineering · General material balance equation for oil reservoirs true vertical depth of the middle of the perforated interval, m Well testing · Well inflow: the well performance diagram height of the accumulation at the crest, z 1 − z crest z_1 - z_{\text{crest}} z 1 − z crest , m Well testing · Perched and tilted contacts, trapped water thickness of the reservoir, m Simulation · Two-phase upscaling: pseudo-functions footage: the metres drilled by the well (or by a group of wells), m Drilling · Drilling time and cost footage of the bit run, m Drilling · Bit performance and cost per metre footage of the run, m Drilling · Bit performance and cost per metre true vertical depth of the point from the rotary table, m Drilling · Directional wells: applications and profile true vertical depth of the formation from the rotary table, m Drilling · Offshore and subsea drilling vertical setting depth of the valve, m Production · Completion string equipment true vertical depth of the node; in a vertical well equal to the tubing length, m Production · Nodal analysis of the production system depth of inflow, where the fluid enters the well at the reservoir temperature, m Production · Chokes, surface pressure losses and well temperature true vertical depth of the middle of the perforated interval, m Production · Artificial lift: when it is needed and how to choose the method pressure ratio ( p out − p in ) / ( p pf − p out ) (p_{\text{out}} - p_{\text{in}})/(p_{\text{pf}} - p_{\text{out}}) ( p out − p in ) / ( p pf − p out ) , — Production · Hydraulic pumps: piston and jet true vertical depth, m Production · Gas lift: principles and choice of operating conditions true vertical depth of the liquid level in the annulus, m Production · Unloading a gas lift well: valves and mandrels vertical depth of the interval, m Production · Acid systems and treatment design vertical depth of the middle of the injection interval (for friction, the length of the tubing along the hole; in a vertical well they coincide), m Production · Water injection systems h 1 , h 2 h_1,\ h_2 h 1 , h 2 h d h_d h d h D h_D h D h i h_i h i h k h_k h k h w h_w h w h , ϕ h,\ \phi h , ϕ i i i the reading at which we calculate the derivative, — Well testing · Diagnosis with the pressure derivative number of the unknown being eliminated (the pivot row: the row that we subtract from the rows below it), — Simulation · Solving systems of linear equations in simulators build-up or drop-off rate: degrees per the reference length l 0 l_0 l 0 , °/30 m Drilling · Directional wells: applications and profile dogleg severity in sliding drilling: degrees per the reference length l 0 l_0 l 0 , °/30 m Drilling · Deflection tools and downhole motors dogleg severity: degrees per the reference length l 0 l_0 l 0 , °/30 m Drilling · Directional survey calculations discount rate; for the flow of the whole company, the weighted average cost of capital (the average return that all its lenders and shareholders expect), fraction per year Economics · Valuation methods: book value and market value rate per period, fraction Economics · Interest and compounding rate per compounding period, fraction Economics · Interest and compounding effective annual rate, fraction per year Economics · Interest and compounding equivalent effective annual rate, fraction per year Economics · Interest and compounding rate in nominal money, that is, including inflation, fraction per year Economics · Interest and compounding discount rate per year, fraction Economics · Discounting and present value discount rate, fraction Economics · Discounting and present value discount rate: the required return, fraction per year Economics · Discounting and present value discount rate; d i \dd i d i , fraction Economics · Discounting and present value return (growth rate) of the account or fund, fraction per year Economics · Annuities and discounted production discount rate for money (real), fraction per year Economics · Annuities and discounted production discount rate with a risk premium, fraction per year Economics · Choosing the discount rate nominal rate: in the money of the year concerned, fraction per year Economics · Inflation: nominal and real money return on capital: the interest on the whole investment, 1/year Economics · Annual capital charge discount rate: the return that the investor requires from an investment with this risk, fraction Economics · The state and the subsoil: ownership of resources discount rate, a yearly one, fraction Economics · State regulation of field development the investor's rate, fraction Economics · Petroleum fiscal systems and taxation I I I total number of layers; the sums in the denominators are taken over all the layers, — Geoscience · Descriptive statistics in geology current through the sample, A Logs and petrophysics · Resistivity logs: electrical and induction tools current through the current electrode A A A , A Logs and petrophysics · Resistivity logs: electrical and induction tools electrode current, A Logs and petrophysics · Resistivity logs: electrical and induction tools resistivity index (the factor by which the resistivity increases), — Logs and petrophysics · Archie's equation and saturation of clean reservoirs anisotropy index k h / k v \sqrt{k_h/k_v} k h / k v Horizontal wells , — Reservoir engineering · Reservoir heterogeneity and permeability averaging second moment of area of the section of the pipe body, J / 2 J/2 J /2 , m⁴ Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe second moment of area of the cross-section of the pipe body (a measure of its resistance to bending), m⁴ Drilling · Drill string design ionic strength of the solution: in mol/m³ in the first form, in mol/L in the second, mol/m³; mol/L Drilling · Water-based muds and clay chemistry magnetic dip angle from the survey: the angle between the field vector and the horizontal, degrees Drilling · Survey instruments: magnetic, gyroscopic and inertial second moment of area of the tubing cross-section (how well it resists bending), π ( D 4 − d 4 ) / 64 \pi(D^4 - d^4)/64 π ( D 4 − d 4 ) /64 , m⁴ Production · Completion string equipment anisotropy index, — Production · Horizontal wells current in each conductor of the cable, A Production · Electric submersible pumps (ESP) injectivity index, m³/(d·MPa) Production · Water injection systems average injectivity index over the segment, m³/(d·MPa) Production · Water injection systems capital expenditure: either only the sustaining part or all of it, US$ million/yr Economics · Oil companies and investment investment at the initial moment, US$ million Economics · Cumulative cash flow and payback period capital investment of the project (positive amounts) to which the budget limit applies, US$ million Economics · Acceleration projects and incremental analysis I G R I_{GR} I GR J J J number of layers counted up to this step, — Geoscience · Descriptive statistics in geology pseudo-geometric factor: the share of the invaded zone in the reading; it grows with d i d_i d i , — Logs and petrophysics · Borehole environment: invaded zone and mudcake productivity index of the well for stock-tank oil (the rate the well gives per unit of drawdown), m³/(d·MPa) Reservoir engineering · Reservoir fluid sampling dimensionless capillary pressure, — Reservoir engineering · Capillary pressure and the transition zone productivity index of the aquifer for pseudo-steady-state flow, m³/(d·MPa) Reservoir engineering · Aquifer models: water influx productivity index of the aquifer in pseudo-steady-state flow (the inflow for each unit of pressure difference), m³/(d·MPa) Reservoir engineering · Simplified water influx models: Fetkovich and Carter–Tracy productivity index, m³/(d·MPa) Well testing · Well inflow: the well performance diagram productivity index with respect to the pressure at the outer boundary, m³/(s·Pa) Well testing · Steady-state radial flow productivity index based on the average pressure (metric form), m³/(d·MPa) Well testing · Steady-state radial flow productivity index with respect to the average reservoir pressure, m³/(s·Pa) Well testing · Skin factor productivity index with respect to the average pressure of the area, m³/(s·Pa) Well testing · Well testing: purposes and types of test productivity index of the well, m³/(d·MPa) Well testing · Lumped multi-tank material balance model productivity index of the well (the rate per unit of drawdown), in reservoir volumes of liquid, m³/(d·MPa) Simulation · What a reservoir simulation model is and why it is needed polar moment of inertia of the section of the pipe body, mm⁴ Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe productivity index in terms of the rate at standard conditions, m³/(s·Pa) Production · Horizontal wells productivity index, m³/(d·MPa) Production · Inflow performance relationship (IPR) productivity index of the single-phase part of the curve, m³/(d·MPa) Production · Inflow performance relationship (IPR) average productivity index from a test, q / ( p ˉ R − p w f ) q/(\bar p_R - p_{wf}) q / ( p ˉ R − p w f ) , m³/(d·MPa) Production · Inflow performance relationship (IPR) productivity index; 1 / J 1/J 1/ J , m³/(d·MPa) Production · Well performance sensitivity analysis productivity index with respect to the average reservoir pressure, m³/(s·Pa) Production · Inflow to a hydraulically fractured well J ∗ J^* J ∗ k k k volume of gas from 1 g of pure calcite, found by calibrating the apparatus; about 240 mL/g at 20 °C and atmospheric pressure, mL/g Geoscience · Minerals and rocks permeability, D Geoscience · Sediment texture: grain size, sorting and shape air permeability without the Klinkenberg correction, mD Geoscience · Reservoir quality: geological controls on porosity and permeability attenuation coefficient: how strongly the water absorbs light, 1/m Geoscience · Carbonate sediments, environments and carbonate porosity number of elements assessed, — Geoscience · Petroleum system and the play concept rate constant of a first-order reaction (its speed is proportional to the amount left): the fraction of the kerogen not yet converted that breaks down per unit time, 1/s (or per million years) Geoscience · Source rocks, maturation and migration number of elements, — Geoscience · Geological risk and chance of success permeability of the rock along the fracture set, created by the fractures, m² Geoscience · Fractures and naturally fractured reservoirs increase of velocity per metre of depth, s⁻¹ Geoscience · Seismic interpretation number of samples averaged, — Logs and petrophysics · Log acquisition, processing and presentation permeability, mD Logs and petrophysics · Nuclear magnetic resonance (NMR) logging correction factor from sample 1, — Reservoir engineering · PVT correlations for oil and gas condensate permeability of the rock, m² Reservoir engineering · Rock permeability permeability of the reservoir (horizontal), m² Reservoir engineering · Rock permeability permeability, m² Reservoir engineering · Rock permeability permeability of the sample, m² Reservoir engineering · Capillary pressure and the transition zone absolute (base) permeability, m² Reservoir engineering · Relative permeability permeability of the reservoir, m² Reservoir engineering · Flow regimes permeability (here the same in all directions), m² Reservoir engineering · Diffusivity equation permeability of the reservoir to the mobile fluid, m² Reservoir engineering · Diffusivity equation absolute permeability of the rock, m² Reservoir engineering · Fractional flow function and mobility ratio permeability of the reservoir to the flowing fluid, m² Well testing · Steady-state radial flow permeability of the reservoir, mD Well testing · Skin factor permeability, m² Well testing · Inflow at high rates: non-Darcy flow permeability of the rock, mD Well testing · Inflow at high rates: non-Darcy flow permeability found from the slope, mD Well testing · Pressure drawdown analysis permeability from the build-up, m² Well testing · Nonideal wellbore storage, well clean-up and changing skin permeability from the derivative plateau (radial flow), m² Well testing · Several boundaries: parallel faults and wedge-shaped blocks permeability of the formation, mD Well testing · Partially communicating faults permeability of the cells (the same as for the formation in the test), mD Well testing · Partially communicating faults permeability of the rock at the probe for the fluid that flows in, m² Well testing · Pressure measurement with the wireline formation tester solubility of gas in the base oil: the volume at standard conditions per 1 m³ of base oil for each megapascal, m³/(m³·MPa) Drilling · Oil-based muds increase of strength with depth, kPa/m Drilling · Offshore and subsea drilling permeability of the reservoir to oil, m² Production · Inflow performance relationship (IPR) adiabatic exponent — the ratio of the heat capacities of the gas at constant pressure and at constant volume, c p / c v c_p/c_v c p / c v , — Production · Chokes, surface pressure losses and well temperature reservoir permeability, mD Production · Perforating operations: gun conveyance and procedures permeability of the undamaged reservoir, mD Production · Formation damage and damage skin permeability of the reservoir, mD Production · Hydraulic fracturing: purpose and well selection adiabatic exponent of the gas, c p / c v c_p/c_v c p / c v , — Production · Gas processing and compression permeability of the reservoir (1 mD = 0.987 ⋅ 10 − 15 0.987\cdot 10^{-15} 0.987 ⋅ 1 0 − 15 , m² Production · Water injection systems capital intensity of new production — investment per 1 bbl/d, US$ per bbl/d Economics · Oil companies and investment acceleration factor: 1 for simple declining balance, 2 for double-declining balance, — Economics · Valuation methods: book value and market value number of discoveries, — Economics · Expected monetary value and preference theory K K K bulk modulus: resistance to a change of volume, Pa Geoscience · Structure and composition of the Earth electrochemical coefficient, proportional to the absolute temperature: K ≈ 65 + 0.24 T K \approx 65 + 0.24\,T K ≈ 65 + 0.24 T T T T , mV Logs and petrophysics · Spontaneous potential (SP) log electrochemical coefficient at formation temperature, 65 + 0.24 T 65 + 0.24\,T 65 + 0.24 T , mV Logs and petrophysics · Spontaneous potential (SP) log bulk modulus of the rock together with the fluid in the pores: the resistance to a change of volume, Pa Logs and petrophysics · Sonic log sonde constant: a geometric factor that depends only on the distances between the electrodes, m Logs and petrophysics · Resistivity logs: electrical and induction tools lithology coefficient: 1 for sandstone, about 1.046 for limestone and 1.173 for dolomite, — Logs and petrophysics · Porosity from the neutron log coefficient of the static SP amplitude, 65 + 0.24 T 65 + 0.24\,T 65 + 0.24 T T T T more ), mV per decade Logs and petrophysics · Resistivity ratio methods and movable oil friction loss coefficient in the tubing, MPa/(m³/d)² Well testing · Well inflow: the well performance diagram probe constant from the mobility formula (39.02 for the classic standard probe), mD·MPa·s/(mPa·s·cm³) Well testing · Pressure measurement with the wireline formation tester ratio of the tensions on the two sides of a rotating sheave: 1.04 for roller bearings, 1.09 for plain bearings, — Drilling · Drilling rig: power and hoisting systems lateral load factor (the ratio of the sideways squeeze to the vertical load), — Drilling · Drill string design ratio of the effective stresses ( σ h − p p ) / ( σ v − p p ) (\sigma_h - p_p)/(\sigma_v - p_p) ( σ h − p p ) / ( σ v − p p ) , — Drilling · Fracture gradient and leak-off testing consistency index: the stress at a shear rate of 1 s⁻¹, Pa·sⁿ Drilling · Drilling fluid rheology and flow regimes consistency index, Pa·sⁿ Drilling · Drilling fluid rheology and flow regimes capacity coefficient: a value found from experience and tests. It depends on the mist extractor, the orientation and size of the vessel, the pressure and the tendency of the liquid to foam, m/s Production · Oil treating: separators, dehydration, desalting and stabilisation constant: 1297 for Δ T \Delta T Δ T , °C·kg/kmol Production · Gas processing and compression the investment in the well at the moment production starts, US$ Economics · Annual capital charge capital expressed in money: K = m c K = m c K = m c , US$ million Economics · Risk reduction and diversification K \mathbf{K} K k b k_b k b k b k_{\text{b}} k b k f k_f k f k g k_g k g k G k_G k G k h , k v k_h,\ k_v k h , k v k i k_i k i k i j k_{ij} k ij k j , h j k_j,\ h_j k j , h j k m c k_{mc} k m c k r g , k r o k_{rg},\ k_{ro} k r g , k r o k r o k_{ro} k r o k r o ′ k_{ro}' k r o ′ k s k_s k s k v k_v k v k v , k h k_v,\ k_h k v , k h k x , k y , k z k_x,\ k_y,\ k_z k x , k y , k z k z k_z k z k , h k,\ h k , h permeability and effective thickness of the reservoir, mD, m Reservoir engineering · Performance prediction for solution gas drive reservoirs permeability and thickness of the aquifer, m², m Reservoir engineering · Aquifer models: water influx permeability and net thickness of the reservoir, m², m Well testing · Pseudo-steady-state flow and the shape factor permeability and net thickness of the reservoir beyond the near-wellbore zone, m², m Well testing · Skin factor permeability and thickness of the reservoir, m², m Well testing · Well testing: purposes and types of test permeability and net thickness, m², m Well testing · Build-up in a bounded reservoir and average reservoir pressure permeability of the cell and the open thickness of the formation in it, mD, m Simulation · Well model in a grid block permeability and thickness of the reservoir, mD, m Production · Effect of completion on inflow permeability and net thickness of the reservoir, m², m Production · Acid treatments: principle, economics and candidate selection permeability of the reservoir and thickness of the treated interval, m², m Production · Acid systems and treatment design k , h , μ k,\ h,\ \mu k , h , μ permeability, thickness of the reservoir, viscosity, m², m, Pa·s Reservoir engineering · Diffusivity equation permeability, reservoir thickness, viscosity, m², m, Pa·s Well testing · Inflow at high rates: non-Darcy flow k , ϕ k,\ \phi k , ϕ k , ϕ , μ , c t k,\ \phi,\ \mu,\ c_t k , ϕ , μ , c t permeability, porosity, viscosity, total compressibility, m², —, Pa·s, 1/Pa Well testing · Pseudo-steady-state flow and the shape factor permeability (from the first line), porosity, viscosity, total compressibility, m², —, Pa·s, 1/Pa Well testing · A sealing fault near the well: the method of images permeability, porosity, viscosity, total compressibility, mD, —, mPa·s, 1/MPa Simulation · Pressure equation for single-phase flow L L L wavelength in deep water, m Geoscience · Primary sedimentary structures length of the stretch across the set on which the fractures are counted, m Geoscience · Fractures and naturally fractured reservoirs length of the side between points a a a b b b , m Geoscience · Structure maps and contouring length of the averaging window, about equal to the vertical resolution of the tool, m Logs and petrophysics · Open-hole logging: why, how and when averaging window of the tool itself, about equal to its vertical resolution, m Logs and petrophysics · Log acquisition, processing and presentation sonde reading in the volume of investigation, units of the method Logs and petrophysics · Overview of logging tools distance between the transmitter and the receiver along the tool, m Logs and petrophysics · Sonic log length of the sample along the current, m Logs and petrophysics · Resistivity logs: electrical and induction tools reading of a method: bulk density, neutron porosity or interval transit time, g/cm³; fraction; µs/m Logs and petrophysics · Lithology and porosity from crossplots distance between the outer scales, mm Logs and petrophysics · Interpretation charts: how to read them length of the capillary, m Reservoir engineering · Laboratory PVT tests length of the flow path, m Reservoir engineering · Rock permeability distance along the reservoir, for example between an injection well and a producing well, m Reservoir engineering · Reservoir heterogeneity and permeability averaging distance from the well to the fault; 2 L 2L 2 L , m Reservoir engineering · Superposition principle distance from the well to the constant-pressure boundary, m Reservoir engineering · Superposition principle distance between the rows of injection and production wells, m Reservoir engineering · Displacement in heterogeneous reservoirs length of the sample, m Well testing · Inflow at high rates: non-Darcy flow distance from the well to the boundary; the image is at the distance 2 L 2L 2 L , m Well testing · Diagnosis with the pressure derivative differentiation interval, in fractions of a decimal logarithmic cycle, — Well testing · Diagnosis with the pressure derivative distance to the fault, m Well testing · A sealing fault near the well: the method of images distance to the fault, known from geology or seismic, m Well testing · A sealing fault near the well: the method of images distance from the well to the fault, m Well testing · Partially communicating faults length of the area (the long side), m Well testing · Reservoir limit test length of the rectangular area (the long side), m Well testing · Build-up in a bounded reservoir and average reservoir pressure vertical distance from the mean depth of the water points to the contact, m Well testing · Two-phase flow and reservoir description from formation-tester data length of the block along the flow, m Simulation · Permeability upscaling for single-phase flow distance over which the flow changes noticeably: between wells, the width of the displacement front, the zone of radial inflow near a well, m Simulation · Special topics in upscaling length of the piston stroke, m Drilling · Rig circulating and rotary systems half the distance between tool joints (for length range 2 pipe, about 4.6 m), m Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe length of the section along the hole, m Drilling · Drill string design depth from which the bit is pulled: the length of the string along the hole (in a deviated well, more than the true vertical depth), m Drilling · Bit performance and cost per metre characteristic compaction depth: at depth L L L e ≈ 2.72 \e \approx 2.72 e ≈ 2.72 , m Drilling · Pore pressure and overburden pressure length of the pipe pulled, m Drilling · Well control: primary barrier and kick indicators depth of the mud level in the string, measured from the wellhead, m Drilling · Casing design depth of the shoe, m Drilling · Casing design length of the interval drilled, m Drilling · Solids control in drilling fluids length of the channel, m Drilling · Drilling fluid rheology and flow regimes length of the well from the zero datum to the target, m Drilling · Directional wells: applications and profile distance from the bit to the upper stabiliser, m Drilling · Deflection tools and downhole motors length of the string from the module to the standpipe, m Drilling · Measurement while drilling length of the riser (here, the sea depth), m Drilling · Offshore and subsea drilling length of the tubing from the hanger to the packer, m Production · Completion string equipment length of line on which Δ F \Delta F Δ F , m Production · Wireline operations length of the horizontal section that opens the formation, m Production · Horizontal wells length of a tunnel with gravel: from the screen through the casing and cement to the reservoir wall, m Production · Effect of completion on inflow length of the rod string (along the wellbore), m Production · Sucker-rod pumping length of the rod string and of the tubing down to the pump, m Production · Sucker-rod pumping length of the rod string, m Production · Sucker-rod pumping length of the tubing from the pump to the wellhead, m Production · Progressing cavity pumps and hybrid systems length of the continuous jet, mm Production · Shaped-charge perforating liquid capacity of the facilities: oil and water together, m³/d Production · Field development concepts: surface facilities impairment loss, by which the book value is reduced, US$ million Economics · Valuation methods: book value and market value l 0 l_0 l 0 L 1 L_1 L 1 L c L_c L c L i L_i L i L , H L,\ H L , H lg \lg lg ln \ln ln m m m mass of the sample, g Geoscience · Minerals and rocks mean of the natural logarithms of the sample, — Geoscience · Distributions and sample size most likely value (the mode), units of the parameter Geoscience · Probabilistic volumetrics by Monte Carlo simulation slope of the line: the drop in temperature per logarithmic cycle (one tenfold change of the ratio). It depends on the cooling power and on the thermal conductivity of the rocks, °C Logs and petrophysics · Formation water and formation temperature cementation exponent, an empirical exponent, — Logs and petrophysics · Archie's equation and saturation of clean reservoirs slope of the line (per logarithmic cycle), °C Reservoir engineering · Reservoir pressure and temperature coefficient that depends on the acentric factor (forms below), — Reservoir engineering · Cubic equations of state coefficient of the temperature function α ( T ) \alpha(T) α ( T ) , — Reservoir engineering · Cubic equations of state exponent, increasing with pressure, — Reservoir engineering · Oil viscosity and interfacial tension mobility of the mixture in the condensate zone relative to the mobility of the gas outside it, — Reservoir engineering · Retrograde condensation, wax, asphaltenes and high-pressure fluids ratio of the initial reservoir volume of the gas cap to the reservoir volume of the oil, — Reservoir engineering · Reservoir drive mechanisms ratio of the initial reservoir volume of the gas cap to the initial reservoir volume of the oil, — Reservoir engineering · General material balance equation for oil reservoirs gas cap ratio, — Reservoir engineering · General material balance equation for oil reservoirs gas cap ratio, known from geological data, — Reservoir engineering · Straight-line material balance (Havlena–Odeh method) ratio of the reservoir volume of the gas cap to the reservoir volume of the oil, — Reservoir engineering · Why water is injected: pressure maintenance and oil displacement slope of the semilog straight line per decimal logarithmic cycle (absolute value), MPa/cycle Well testing · Skin factor pressure drop over one decimal cycle of time on the line, Pa Well testing · Pressure drawdown analysis pressure drop per decimal cycle of time on the line, MPa Well testing · Pressure drawdown analysis slope of the line per decimal logarithmic cycle, Pa Well testing · Pressure build-up analysis slope of the line per logarithmic cycle, MPa Well testing · Pressure build-up analysis slope per logarithmic cycle, the same as for the Horner line, MPa Well testing · Pressure build-up analysis slope of the straight line against lg Δ t e \lg\Delta t_e lg Δ t e , MPa Well testing · Effect of producing time on build-up analysis slope of the Horner line per decimal cycle (positive), Pa Well testing · Build-up in a bounded reservoir and average reservoir pressure slope of radial flow, MPa Well testing · Build-up in a bounded reservoir and average reservoir pressure slope of the line per unit of X B U X_{BU} X B U 2.149 q n B μ / ( k h ) 2.149\,q_nB\mu/(kh) 2.149 q n B μ / ( k h ) , MPa Well testing · Equivalent producing time and synthetic flowing time slope of the line per decimal logarithmic cycle (per tenfold change on the logarithmic axis), MPa Well testing · Comparing formation-tester, core and well-test data mass of a metre of plain drill collar (not allowing for grooves and spiral flutes), kg/m Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe mass per metre. For drill collars, use the formula for a plain pipe. For drill pipe and HWDP, use the adjusted mass from the catalogue (“adjusted weight”), which includes the tool joints and the upsets (the thickened pipe ends), kg/m Drilling · Drill string design mass of a metre of pipe, kg/m Drilling · Drill string design mass of a metre of plain pipe, without couplings, kg/m Drilling · Casing: purpose, types, properties and standards nominal weight (mass per metre) of the pipe with couplings, kg/m Drilling · Wellheads and running casing mass of a metre of plain pipe (without couplings), kg/m Drilling · Casing design mass of the reagent, kg Drilling · Water-based muds and clay chemistry molality: moles of salt per 1 kg of water, mol/kg Drilling · Oil-based muds exponent of the system losses, — Drilling · Bit hydraulics optimisation mass of a metre of collars, kg/m Drilling · Deflection tools and downhole motors slope (absolute value) of the line “pressure against G G G , Pa Production · Fracture design: size and conductivity number of compounding periods in a year: 2, 4, 12, 365…, — Economics · Interest and compounding number of compoundings in a year, — Economics · Interest and compounding margin per barrel before income tax: m = P ( 1 − r ) − v m = P(1 - r) - v m = P ( 1 − r ) − v , US$/bbl Economics · Acceleration projects and incremental analysis margin per barrel before income tax, US$/bbl Economics · Acceleration projects and incremental analysis marginal government take: the part of the increase in the flow before payments that the payments take, fraction Economics · Petroleum fiscal systems and taxation number of outcomes, — Economics · Expected monetary value and preference theory how many stakes the capital can bear: the integer part of the ratio of the capital to the stake, — Economics · Risk reduction and diversification M M M share of matrix in the sum of framework and matrix, % Geoscience · Sedimentary rocks and their classification detrital clay matrix between the grains, % Geoscience · Reservoir quality: geological controls on porosity and permeability mass of hydrocarbons generated, kg Geoscience · Source rocks, maturation and migration anomalous mass of the body — excess (positive) or deficit (negative), kg Geoscience · Geophysical exploration methods total anomalous mass of all bodies below the plane, kg Geoscience · Geophysical exploration methods molar mass of the molecule, g/mol Logs and petrophysics · Density log and photoelectric factor (Pe) magnetisation at the start of the measurement, relative units Logs and petrophysics · Nuclear magnetic resonance (NMR) logging molar mass of the gas, 28.97 γ g 28.97\,\gamma_g 28.97 γ g , kg/kmol Reservoir engineering · Reservoir pressure and temperature molar (average) mass of the mixture, g/mol = kg/kmol Reservoir engineering · Composition of reservoir fluids misfit function (a number that shows how far the calculation is from the measurements), — Reservoir engineering · History matching of aquifer parameters molar mass of the gas, kg/mol Well testing · Inflow at high rates: non-Darcy flow ratio of the mobilities of gas and oil at the current gas saturation, — Well testing · Two-phase flow and reservoir description from formation-tester data misfit function — the mean square of the normalised discrepancy, — Simulation · History matching number of stored numbers of the Cholesky decomposition (for the LU decomposition it is twice as many: L \mathbf{L} L U \mathbf{U} U , — Simulation · Solving systems of linear equations in simulators torque on the string at the surface, kN·m Drilling · Rig circulating and rotary systems friction torque on the section when rotating, N·m Drilling · Drill string design torque at the bit, N·m Drilling · Bit performance and cost per metre molar mass of the gas (about 0.0174 kg/mol for a natural gas with a specific gravity of 0.6 relative to air), kg/mol Drilling · Pore pressure and overburden pressure torque on the shaft, N·m Drilling · Deflection tools and downhole motors ratio of the flow rates of the production and of the power fluid, — Production · Hydraulic pumps: piston and jet torque at the polished rod, N·m Production · Progressing cavity pumps and hybrid systems the torque that is passed, N·m Production · Progressing cavity pumps and hybrid systems molar mass of the gas, 0.02897 γ g 0.02897\,\gamma_{\text{g}} 0.02897 γ g γ g \gamma_{\text{g}} γ g , kg/mol Production · Gas lift: principles and choice of operating conditions mass of proppant, kg Production · Fracture design: size and conductivity mass of gravel, kg Production · Sand control methods molar mass of the inhibitor: methanol 32.04, MEG 62.07, kg/kmol Production · Gas processing and compression molar mass of the component: hydrogen sulfide 34.08, g/mol Production · Gas processing and compression molar mass of the gas, kg/mol Production · Gas processing and compression equal yearly margin before income tax: the revenue of the asset less the operating costs, US$ million a year Economics · Annual capital charge M 0 M_0 M 0 m i m_i m i M ′ M' M ′ m ( p ) m(p) m ( p ) Δ p margin \Delta p_{\text{margin}} Δ p margin Δ t max \Delta t_{\max} Δ t m a x n n n number of points counted, — Geoscience · Sedimentary rocks and their classification number of measurements, — Geoscience · Primary sedimentary structures number of prospects, — Geoscience · Geological risk and chance of success number of prospects drilled, — Geoscience · Geological risk and chance of success number of layers above the boundary, — Geoscience · Geophysical exploration methods fold, the number of traces added at one CMP, — Geoscience · Seismic acquisition and processing number of points taken into account: all of them, or the nearest ones within the search radius, — Geoscience · Structure maps and contouring number of vertices; we go round them in order, clockwise or anticlockwise, — Geoscience · Gross rock volume from maps number of slices; it must be even, — Geoscience · Gross rock volume from maps number of data points in the neighbourhood, — Geoscience · Spatial correlation and the variogram number of trials, — Geoscience · Probabilistic volumetrics by Monte Carlo simulation count rate opposite the given bed, counts per second Logs and petrophysics · Gamma ray log and natural gamma ray spectrometry mean number of elastic collisions, — Logs and petrophysics · Neutron log saturation exponent, an empirical exponent, — Logs and petrophysics · Archie's equation and saturation of clean reservoirs saturation exponent, — Logs and petrophysics · Determining formation water resistivity the chosen saturation exponent, — Logs and petrophysics · Resistivity–porosity crossplots amount of gas (number of moles), mol Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) number of samples, — Reservoir engineering · PVT correlations for oil and gas condensate effective carbon number of the C7+ fraction, — Reservoir engineering · Equilibrium ratios: correlations and equations of state number of the current rate step: t n − 1 < t t_{n-1} < t t n − 1 < t , — Reservoir engineering · Superposition principle number of measurements, — Well testing · Type-curve matching exponent: 1 for wellbore storage or a closed area, ½ for linear flow, — Well testing · Diagnosis with the pressure derivative number of points, — Well testing · Comparing formation-tester, core and well-test data number of independent pairs “pretest and core”, — Well testing · Comparing formation-tester, core and well-test data number of these points, — Well testing · Forced-gradient technique and multi-well analysis number of unknowns, — Simulation · Solving systems of linear equations in simulators number of the well in the series: 1, 2, 3 …, — Drilling · Drilling time and cost number of working lines, — Drilling · Drilling rig: power and hoisting systems strokes per minute, strokes/min Drilling · Rig circulating and rotary systems number of revolutions of the bit in a run; usually given in thousands, rev Drilling · Bit selection and dull grading flow behaviour index of the power-law model of the fluid, — Drilling · Primary cementing flow behaviour index; n < 1 n < 1 n < 1 n = 1 n = 1 n = 1 n > 1 n > 1 n > 1 , — Drilling · Drilling fluid rheology and flow regimes flow behaviour index, — Drilling · Drilling fluid rheology and flow regimes flow behaviour index in the given section, — Drilling · Circulating pressure losses flow behaviour index; for pipes, from the readings at 600 and 300 rpm, — Drilling · Circulating pressure losses rotational speed of the shaft, rev/s (multiply by 60 for rpm) Drilling · Deflection tools and downhole motors number of bits for one quantity (rounded up), bit Drilling · Measurement while drilling length of the buckled section above the packer (up to the neutral point, where the buckling force falls to zero), m Production · Completion string equipment exponent: 1 for purely viscous flow, down to 0.5 with strong inertial losses, — Production · Inflow performance relationship (IPR) exponent: 1 for purely viscous flow, down to 0.5 when inertial losses dominate, — Production · Inflow performance relationship (IPR) number of open tunnels in the interval, — Production · Effect of completion on inflow number of strokes (double strokes) per minute, min⁻¹ Production · Sucker-rod pumping number of strokes per minute, min⁻¹ Production · Sucker-rod pumping number of double strokes per minute, min⁻¹ Production · Hydraulic pumps: piston and jet rotational speed of the rotor, rpm Production · Progressing cavity pumps and hybrid systems rotational speed, rpm Production · Progressing cavity pumps and hybrid systems number of perforation holes per metre, 1/m Production · Sources of formation damage flow behaviour index, — Production · Fracturing fluids and tip-screenout fracturing number of stages, — Production · Gas processing and compression number of years elapsed, years Economics · Valuation methods: book value and market value number of periods, — Economics · Interest and compounding number of periods; project calculations also allow a fractional value, — Economics · Interest and compounding term, years Economics · Interest and compounding number of years from the base year, years Economics · Interest and compounding time from the origin to the payment; it need not be a whole number, years Economics · Discounting and present value length of the investment, years Economics · Discounting and present value number of payments (years), — Economics · Annuities and discounted production number of annual payments whose present value equals P V PV P V , years Economics · Annuities and discounted production number of payments, — Economics · Annuities and discounted production number of years between the values I 0 I_0 I 0 I n I_n I n , — Economics · Inflation: nominal and real money the last year at whose end the cumulative flow is still negative, — Economics · Cumulative cash flow and payback period number of payments: the service life of the asset, years Economics · Annual capital charge service life of the option, years Economics · Annual capital charge number of wells in the programme, — Economics · Expected monetary value and preference theory N N N total number of transitions, — Geoscience · Facies, facies successions and sedimentary logs number of event beds in the element studied — there are N − 1 N - 1 N − 1 , — Geoscience · Coastal, shallow-marine and deep-marine environments number of fractures of the set crossed by the well in the interval, — Geoscience · Fractures and naturally fractured reservoirs number of active channels of the spread, — Geoscience · Seismic acquisition and processing number of measurements, — Geoscience · Descriptive statistics in geology number of plugs, — Geoscience · Descriptive statistics in geology number of independent measurements, — Geoscience · Distributions and sample size oil initially in place at standard conditions (STOIIP ), m³ Geoscience · Volumetric estimation of hydrocarbons in place oil initially in place, m³ or t Geoscience · Volumetric estimation of hydrocarbons in place the result, a product of factors x j x_j x j ϕ \phi ϕ 1 − S w 1 - S_w 1 − S w 1 / B o i 1/B_{oi} 1/ B o i , million m³ Geoscience · Probabilistic volumetrics by Monte Carlo simulation number of depths compared, — Logs and petrophysics · Log acquisition, processing and presentation number of decades across the width of the grid, — Logs and petrophysics · Log acquisition, processing and presentation number of counts per sample, — Logs and petrophysics · Gamma ray log and natural gamma ray spectrometry count rate of the detector in the energy window of Compton scattering, counts per second Logs and petrophysics · Density log and photoelectric factor (Pe) number of cycles averaged into one point, — Logs and petrophysics · Nuclear magnetic resonance (NMR) logging oil initially in place, m³ (standard conditions) Reservoir engineering · Reservoir engineering: tasks across the life of a field number of stages, including the stock tank, — Reservoir engineering · Separator calculations and optimum separator pressure stock-tank oil initially in place (STOIIP): the oil in place, converted to standard conditions (surface pressure and temperature), m³ Reservoir engineering · Porosity number of wells, — Reservoir engineering · Superposition principle stock-tank oil initially in place (at standard conditions), m³ Reservoir engineering · Reservoir drive mechanisms oil in place at standard conditions, m³ Reservoir engineering · General material balance equation for oil reservoirs oil in place, m³ Reservoir engineering · General material balance equation for oil reservoirs intercept on the vertical axis: the oil in place, m³ Reservoir engineering · Straight-line material balance (Havlena–Odeh method) oil in place: known, m³ Reservoir engineering · History matching of aquifer parameters number of measurements, — Simulation · History matching number of rings, — Simulation · Grids in reservoir simulation models number of cells between the injection and production wells, — Simulation · Grids in reservoir simulation models rotary speed of the bit, counting the speed of the motor if there is one in the bottom hole assembly (BHA, the tools just above the bit), rpm Drilling · Drill bits: types and design rotary speed of the bit: that of the rotary table or the top drive (the motor that turns the string from above) plus that of the shaft of the downhole motor, rpm Drilling · Bit selection and dull grading rotary speed of the bit, rev/s Drilling · Bit performance and cost per metre rotary speed, rpm Drilling · Bit performance and cost per metre number of pump strokes from the start of pumping the kill mud, — Drilling · Well kill methods rotational speed of the sleeve, rpm Drilling · Drilling fluid rheology and flow regimes hydraulic power — the useful work of lifting the liquid per unit of time, W Production · Artificial lift: when it is needed and how to choose the method power at the polished rod, W Production · Progressing cavity pumps and hybrid systems electric power to be generated, W Production · Field development concepts: surface facilities useful life, years Economics · Valuation methods: book value and market value life of the project, years Economics · Cumulative cash flow and payback period remaining reserves of the well, the same before and after the treatment, bbl Economics · Acceleration projects and incremental analysis N 0 N_0 N 0 N 1 , N 2 N_1,\ N_2 N 1 , N 2 N el N_{\text{el}} N el N p N_p N p N s N_s N s n w , n o n_w,\ n_o n w , n o N T G \mathrm{NTG} NTG p p p proportion of the component from the count, fraction Geoscience · Sedimentary rocks and their classification pore pressure, MPa Geoscience · Fractures and naturally fractured reservoirs exponent; usually 2, — Geoscience · Structure maps and contouring reservoir pressure, absolute, MPa Geoscience · Volumetric estimation of hydrocarbons in place a probability estimated as a share of the trials, for example the share of results below a given value, fraction Geoscience · Probabilistic volumetrics by Monte Carlo simulation absolute pressure of the gas, MPa or kPa Reservoir engineering · Composition of reservoir fluids absolute pressure, MPa Reservoir engineering · Gas formation volume factor, compressibility and viscosity pressure, MPa Reservoir engineering · Density and compressibility of reservoir oil absolute pressure, not below the bubble point pressure, psia Reservoir engineering · Density and compressibility of reservoir oil pressure, not above the bubble point pressure of the oil, psia Reservoir engineering · PVT correlations for oil and gas condensate absolute pressure in the system, MPa Reservoir engineering · Vapour–liquid equilibrium pressure of the reading, below the bubble point pressure, MPa Reservoir engineering · Laboratory PVT tests pressure of the step, absolute, MPa Reservoir engineering · Laboratory PVT tests pressure applied to this volume, MPa Reservoir engineering · Rock compressibility and the effect of stress on core properties pore (reservoir) pressure, MPa Reservoir engineering · Rock compressibility and the effect of stress on core properties pressure at the contact (the average pressure of the accumulation), MPa Reservoir engineering · Simplified water influx models: Fetkovich and Carter–Tracy pressure at the gauge, MPa Well testing · Pressure measurement with the wireline formation tester pressure in the “tank”, the same throughout the volume, MPa Simulation · What a reservoir simulation model is and why it is needed pressure in the cell, bar (MPa) Simulation · Building a simulation model: input data and results observed order of convergence: when the grid is refined twofold, the error falls by a factor of 2 p 2^{p} 2 p , — Simulation · Grids in reservoir simulation models pressure; if gravity is taken into account, the potential p − ρ g D p - \rho g D p − ρ g D ρ \rho ρ , Pa Simulation · Pressure equation for single-phase flow pressure at depth h h h , Pa Drilling · Pore pressure and overburden pressure gauge pressure at depth h h h , Pa Drilling · Pore pressure and overburden pressure absolute pressure at the depth z z z , Pa Drilling · Well control: primary barrier and kick indicators pressure, Pa Production · Multiphase flow in tubing absolute pressure at the cross-section, Pa Production · Multiphase flow in tubing absolute pressure of the gas, psia Production · Chokes, surface pressure losses and well temperature pressure at the front of the jet, Pa Production · Shaped-charge perforating probability of the high forecast, fraction Economics · Market, financial and regulatory uncertainty P P P sinuosity, — Geoscience · Continental environments: aeolian and fluvial P shears, which are also synthetic but rotated the other way; they appear later than R shears and link them, — Geoscience · Structural styles and tectonic history probability that a body penetrated by one well is also penetrated by the other, — Geoscience · Well correlation tolerance — the permissible deviation of the mean of the samples from the true mean, % of the mean Geoscience · Distributions and sample size mass fraction of dissolved salt, fraction Logs and petrophysics · Neutron log mass fraction of NaCl in the filtrate, fraction Logs and petrophysics · Porosity from the density log number of phases in equilibrium, — Reservoir engineering · Phase behaviour: pure substances and binary mixtures fraction of the pressure drop at the contact reached at a point of the aquifer, ( p i − p ) / Δ p (p_i - p)/\Delta p ( p i − p ) /Δ p , — Reservoir engineering · Unsteady-state water influx: the van Everdingen–Hurst method weight of the string in mud below the section considered. In a deviated well, use the force in this section when pulling out, N Drilling · Drill string design load on the polished rod, N Production · Sucker-rod pumping depth of the tunnel in the target, mm Production · Shaped-charge perforating external pressure on the sample, MPa Production · Sand production: types, prediction and cost of the problem field price, $/bbl Economics · Cash flow model of an oil and gas project present value of the deal “invest now, receive in n n n , US$ million Economics · Discounting and present value field price (the price received at the field), the same in all years, $/bbl Economics · Annuities and discounted production price at the field, constant in all years, $/bbl Economics · Unit costs per barrel the years in which payments are made, usually the years of operation of the asset, — Economics · Annual capital charge price at the field, constant, US$/bbl Economics · The state and the subsoil: ownership of resources price of gas at the inlet of the gas processing plant (GPP), which is the netback of the gas, US$ per thousand m³ Economics · State regulation of field development p 0 p_0 p 0 any reference pressure (usually zero or atmospheric); only differences of m m m , MPa Reservoir engineering · Gas formation volume factor, compressibility and viscosity initial pressure in the chamber with the sample, usually atmospheric, kPa, absolute Reservoir engineering · Porosity any reference pressure: only the difference of the pseudo-pressures enters the equation, Pa Well testing · Steady-state radial flow pressure of the cell with the well , calculated by the simulator, MPa Simulation · Well model in a grid block pressure above the column: atmospheric pressure for an open well (zero in gauge units), the wellhead pressure for a closed well, Pa Drilling · Pore pressure and overburden pressure initial pressure of the nitrogen in the bottle with no fluid (absolute), MPa Drilling · Blowout prevention equipment p 1 p_1 p 1 p 1 − p 2 p_1 - p_2 p 1 − p 2 p 1 , p 2 p_1,\ p_2 p 1 , p 2 absolute pressures of the reference conditions, the same units Reservoir engineering · Systems of units: SI, oilfield and metric oilfield pressures of the two readings, MPa Reservoir engineering · Laboratory PVT tests pressure at the inlet and at the outlet, Pa Reservoir engineering · Rock permeability absolute pressure at the inlet and the outlet of the sample, Pa Reservoir engineering · Rock permeability absolute pressures (measured from zero, not from atmospheric pressure) at the inlet and outlet of the sample, Pa Well testing · Inflow at high rates: non-Darcy flow pressure just on each side of the zone, Pa Well testing · Partially communicating faults absolute pressures, MPa Drilling · Well control: primary barrier and kick indicators absolute pressure upstream and downstream of the choke, MPa Production · Chokes, surface pressure losses and well temperature pressure upstream and downstream of the choke, MPa Production · Chokes, surface pressure losses and well temperature absolute pressures at the compressor inlet and outlet, Pa Production · Gas lift: principles and choice of operating conditions p ann p_{\text{ann}} p ann p b p_b p b bubble point pressure of the mixture at temperature T T T , MPa Reservoir engineering · Phase behaviour: pure substances and binary mixtures bubble point pressure, absolute, psia Reservoir engineering · PVT correlations for oil and gas condensate bubble point pressure, psia Reservoir engineering · PVT correlations for oil and gas condensate bubble point pressure (for an oil, the saturation pressure), MPa Reservoir engineering · Vapour–liquid equilibrium bubble point pressure at the temperature of the test, MPa Reservoir engineering · Laboratory PVT tests absolute pressure at which the flow rate is measured (usually close to atmospheric), Pa Reservoir engineering · Rock permeability breakdown pressure, MPa Drilling · Fracture gradient and leak-off testing bubble point pressure, MPa Production · Inflow performance relationship (IPR) breakdown pressure of the wall at the bottom of the well, MPa Production · Rock mechanics for hydraulic fracturing p c p_c p c capillary pressure: the difference between the oil and water pressures at height h h h , Pa Reservoir engineering · Fluid saturation capillary pressure, Pa Reservoir engineering · Capillary pressure and the transition zone capillary pressure at water saturation S w S_w S w , Pa Reservoir engineering · Capillary pressure and the transition zone capillary pressure p o − p w p_o - p_w p o − p w , Pa Reservoir engineering · Fractional flow function and mobility ratio pressure of the gas pocket after the gas and liquid have separated, Pa Well testing · Nonideal wellbore storage, well clean-up and changing skin capillary pressure, MPa Simulation · Petrophysical input for simulation: relative permeability and capillary pressure fracture closure pressure ; in a uniform reservoir it equals σ h \sigma_h σ h , MPa Production · Rock mechanics for hydraulic fracturing closure pressure of the fracture , the minimum horizontal stress in the reservoir, MPa Production · Fracture design: size and conductivity P c P_c P c p c ( S w ) p_c(S_w) p c ( S w ) p d p_d p d p D p_D p D dimensionless pressure at the wall of the well at a constant rate, without skin; in an infinite reservoir 1 2 ( ln t D + 0.809 ) \tfrac12(\ln t_D + 0.809) 2 1 ( ln t D + 0.809 ) , — Reservoir engineering · Superposition principle dimensionless pressure drop of a well without wellbore storage at the time we look at; usually between 5 and 15, — Well testing · Wellbore storage dimensionless change of pressure, 2 π k h Δ p / ( q B μ ) 2\pi kh\,\Delta p/(qB\mu) 2 π k h Δ p / ( q B μ ) , — Well testing · Type-curve matching dimensionless change of pressure in the well itself, 2 π k h Δ p / ( q B μ ) 2\pi kh\,\Delta p/(qB\mu) 2 π k h Δ p / ( q B μ ) Line-source solution and the pressure function and Type-curve matching , — Well testing · Diagnosis with the pressure derivative dimensionless drop in bottomhole pressure 2 π k h Δ p / ( q B μ ) 2\pi kh\,\Delta p/(qB\mu) 2 π k h Δ p / ( q B μ ) Line-source solution and the pressure function , — Well testing · A sealing fault near the well: the method of images dimensionless pressure drop at the bottom, 2 π k h Δ p / ( q B μ ) 2\pi kh\,\Delta p/(qB\mu) 2 π k h Δ p / ( q B μ ) , — Well testing · Several boundaries: parallel faults and wedge-shaped blocks dimensionless drop of the bottomhole pressure 2 π k h Δ p / ( q B μ ) 2\pi kh\,\Delta p/(qB\mu) 2 π k h Δ p / ( q B μ ) , — Well testing · Partially communicating faults p D ′ p_D' p D ′ p D ( t D ) p_D(t_D) p D ( t D ) p e p_e p e p e , p w p_e,\ p_w p e , p w p f p_f p f P g P_g P g geological chance of success: the well will find moveable hydrocarbons (hydrocarbons that can flow), fraction Geoscience · Petroleum system and the play concept geological chance of success: all the elements have worked, fraction Geoscience · Geological risk and chance of success geological chance of success, fraction Geoscience · Geological risk and chance of success geological chance of success (the chance of discovery): the probability of finding a significant quantity of moveable hydrocarbons (Geological risk and chance of success ), fraction Geoscience · Classification of reserves and resources chance of success of the well, fraction Economics · Expected monetary value and preference theory chance of success of one well, the same for all, fraction Economics · Expected monetary value and preference theory chance of success before the information, fraction Economics · Decision trees and the value of information prior probability of an accumulation, before the data, P ( H ) P(H) P ( H ) , fraction Economics · Decision trees and the value of information prior probability of an accumulation, fraction Economics · Decision trees and the value of information p i p_i p i partial pressure of component i i i , MPa or kPa Reservoir engineering · Composition of reservoir fluids initial reservoir pressure, Pa Reservoir engineering · Flow regimes initial reservoir pressure (the pressure before the first start), Pa Reservoir engineering · Superposition principle initial pressure, which is also the pressure at the boundary, Pa Reservoir engineering · Superposition principle initial pressure (of the aquifer and the accumulation), MPa Reservoir engineering · Simplified water influx models: Fetkovich and Carter–Tracy initial reservoir pressure, Pa Well testing · Pseudo-steady-state flow and the shape factor reservoir pressure before start-up (initial reservoir pressure), Pa Well testing · Pressure drawdown analysis reservoir pressure before the well is started up, MPa Well testing · Pressure drawdown analysis pressure in the reservoir before start-up, Pa Well testing · A sealing fault near the well: the method of images initial reservoir pressure, MPa Simulation · What a reservoir simulation model is and why it is needed partial pressure of component i i i , kPa Production · Gas processing and compression partial pressure of the component: the pressure it would create if it occupied the whole volume alone, kPa Production · Produced water: composition, treatment and disposal p i , q , B , μ p_i,\ q,\ B,\ \mu p i , q , B , μ initial pressure, rate, formation volume factor, viscosity, Pa, m³/s, m³/m³, Pa·s Reservoir engineering · Line-source solution and the pressure function pressure before start-up, rate, formation volume factor, viscosity, MPa, m³/d, m³/m³, mPa·s Well testing · Pressure drawdown analysis p i , p w f p_i,\ p_{wf} p i , p w f p j p_j p j p k p_k p k P loc P_\text{loc} P loc p out , p in p_{\text{out}},\ p_{\text{in}} p out , p in p p p_p p p pore (reservoir) pressure, MPa Geoscience · Practical structural geology pore pressure, MPa Drilling · Pore pressure and overburden pressure pore pressure of the formation with the highest equivalent mud weight in the open hole, Pa Drilling · Pore pressure and overburden pressure pore pressure at the depth of the estimate, MPa Drilling · Abnormal formation pressures: origin, prediction and recognition pore pressure at this depth, MPa Drilling · Fracture gradient and leak-off testing pore pressure (measured or forecast), MPa Drilling · Fracture gradient and leak-off testing formation (pore) pressure of the formation that has kicked, Pa Drilling · Well kill methods formation pressure, equal to the bottomhole pressure that is held, Pa Drilling · Well kill methods highest pore pressure in the interval that will be drilled with this equipment, Pa Drilling · Blowout prevention equipment pore pressure of the highest-pressure formation of the next interval, at the depth h h h , Pa Drilling · Casing design pore pressure, MPa Production · Rock mechanics for hydraulic fracturing formation (pore) pressure before injection, MPa Production · Rock mechanics for hydraulic fracturing P play P_\text{play} P play P s P_s P s p sat p_{\text{sat}} p sat p sc p_{\text{sc}} p sc p sc , T sc p_{\text{sc}},\ T_{\text{sc}} p sc , T sc p w p_w p w formation water pressure at the depth of the top, Pa Geoscience · Reservoir and seal absolute pressure in the water at depth z z z , Pa Reservoir engineering · Reservoir pressure and temperature pressure at the well wall (bottomhole), Pa Reservoir engineering · Rock permeability pressure at the wall of the well (bottomhole), Pa Well testing · Steady-state radial flow pressure at the wall of an ideal well without skin at the same flow rate, Pa Well testing · Skin factor bottomhole pressure at the level of the bottom perforations, Pa Well testing · Water and gas coning bottomhole pressure, Pa Well testing · Wellbore storage bottomhole pressure opposite the interval, Pa Production · Acid systems and treatment design bottomhole pressure: wellhead pressure plus hydrostatic pressure minus friction, Pa Production · Acid systems and treatment design pressure in the well at this depth, MPa Production · Rock mechanics for hydraulic fracturing bottomhole pressure during injection (for producing wells the bottomhole pressure is written p w f p_{wf} p w f , MPa Production · Water injection systems p w D p_{wD} p w D p well p_{\text{well}} p well p w f p_{wf} p w f bottomhole flowing pressure of the producing well a time t t t , Pa Reservoir engineering · Line-source solution and the pressure function bottomhole pressure at flow rate q q q , MPa Well testing · Well inflow: the well performance diagram actual bottomhole flowing pressure of the producing well, Pa Well testing · Steady-state radial flow bottomhole pressure, Pa Well testing · Pseudo-steady-state flow and the shape factor actual bottomhole flowing pressure of the working well, Pa Well testing · Skin factor bottomhole flowing pressure of the working well, Pa Well testing · Skin factor bottomhole flowing pressure of the producing well, Pa Well testing · Inflow at high rates: non-Darcy flow bottomhole flowing pressure at time t t t , Pa Well testing · Well testing: purposes and types of test bottomhole pressure at time t t t , Pa Well testing · Pressure drawdown analysis bottomhole pressure at the moment of shut-in, Pa Well testing · Nonideal wellbore storage, well clean-up and changing skin bottomhole pressure of the well, MPa Well testing · Lumped multi-tank material balance model bottomhole flowing pressure of the well (the pressure at the bottom of the flowing well), constant, MPa Simulation · What a reservoir simulation model is and why it is needed bottomhole flowing pressure, MPa Simulation · What a reservoir simulation model is and why it is needed bottomhole pressure (at the reference depth of the well), MPa Simulation · Well model in a grid block common bottomhole pressure (referred to one depth), MPa Simulation · Well model in a grid block bottomhole pressure at the datum depth, MPa Production · Multiple-zone completions: commingled and segregated production bottomhole flowing pressure needed to lift the rate q q q , Pa Production · Nodal analysis of the production system bottomhole pressure while the well is flowing, MPa Production · Inflow performance relationship (IPR) bottomhole pressure, MPa Production · Inflow performance relationship (IPR) bottomhole pressure at the middle of the perforated interval, Pa Production · Artificial lift: when it is needed and how to choose the method bottomhole pressure during injection, MPa Production · Rock mechanics for hydraulic fracturing bottomhole pressure while the well is working, MPa Production · Fracture design: size and conductivity bottomhole pressure during production, MPa Production · Sand production: types, prediction and cost of the problem p w f ( t ) p_{wf}(t) p w f ( t ) p w h p_{wh} p w h wellhead (tubing head) pressure, MPa Well testing · Well inflow: the well performance diagram wellhead pressure, that is, the pressure in the lubricator (gauge), Pa Production · Wireline operations wellhead pressure, Pa Production · Nodal analysis of the production system pressure upstream of the choke, gauge, psig Production · Chokes, surface pressure losses and well temperature pressure at the wellhead in the tubing, Pa Production · Electric submersible pumps (ESP) pressure in the tubing at the wellhead (tubing head pressure), MPa Production · Gas lift: principles and choice of operating conditions pressure in the tubing at the wellhead (the back pressure of the flowline), MPa (abs.) Production · Unloading a gas lift well: valves and mandrels pressure at the wellhead in the pipes through which the pressure is passed to the interval (above the liquid), Pa Production · Perforating operations: gun conveyance and procedures p wh p_{\text{wh}} p wh p w s p_{ws} p w s p w s ( Δ t ) p_{ws}(\Delta t) p w s ( Δ t ) p , T p,\ T p , T reservoir pressure and temperature — absolute, MPa, K Reservoir engineering · Gas formation volume factor, compressibility and viscosity reservoir pressure and temperature, both absolute, MPa, K Reservoir engineering · Black oil model: solution gas–oil ratio and formation volume factors absolute pressure and temperature of the mixture, MPa, K Reservoir engineering · Vapour–liquid equilibrium absolute pressure and temperature, MPa, K Reservoir engineering · Equilibrium ratios: correlations and equations of state pressure of the step and reservoir temperature, both absolute, MPa, K Reservoir engineering · Laboratory PVT tests absolute pressure (measured from zero, not from atmospheric pressure) and temperature in the separator, MPa, K Production · Oil treating: separators, dehydration, desalting and stabilisation p , q p,\ q p , q p ( r , t ) p(r, t) p ( r , t ) p ( x , y , z , t ) p(x, y, z, t) p ( x , y , z , t ) q q q flow rate through one fracture, m³/s Geoscience · Fractures and naturally fractured reservoirs share of the intergranular volume taken up by dispersed shale, fraction Logs and petrophysics · Water saturation in shaly sands heat flow density (the heat passing through each square metre) from the interior; in sedimentary basins usually 40–80 mW/m², W/m² Reservoir engineering · Reservoir pressure and temperature volumetric flow rate at the conditions of the test, m³/s Reservoir engineering · Laboratory PVT tests volumetric flow rate of the fluid at the conditions of the test (in the reservoir, at reservoir conditions), m³/s Reservoir engineering · Rock permeability rate at reservoir conditions; the surface rate is q / B q/B q / B B B B , m³/s Reservoir engineering · Rock permeability rate at standard conditions, m³/d Reservoir engineering · Flow regimes rate at standard conditions; q B qB q B , m³/s Reservoir engineering · Diffusivity equation flow rate at standard conditions, m³/d Well testing · Well inflow: the well performance diagram liquid flow rate, m³/d Well testing · Well inflow: the well performance diagram flow rate at reservoir conditions; at standard conditions it equals q / B q/B q / B , m³/s Well testing · Steady-state radial flow well flow rate at the same conditions, m³/s Well testing · Pseudo-steady-state flow and the shape factor flow rate at standard conditions; q B qB q B , m³/s Well testing · Skin factor oil rate at standard conditions, m³/s Well testing · Water and gas coning flow rate at reservoir conditions; for a liquid q = q s B q = q_s B q = q s B , m³/s Well testing · Inflow at high rates: non-Darcy flow gas rate at standard conditions, m³/s Well testing · Inflow at high rates: non-Darcy flow well rate at standard conditions, m³/s Well testing · Dimensionless well solutions: skin, radius of investigation and units rate at the wellhead at standard conditions, m³/s Well testing · Wellbore storage change of the rate at the wellhead: the rate after start-up or the rate before shut-in, at standard conditions, m³/s Well testing · Wellbore storage volumetric rate of the draw by the piston, m³/s Well testing · Pressure measurement with the wireline formation tester rate of the draw by the piston, m³/s Well testing · Supercharging and permeability from formation-tester pretests change in the rate of the well in unit 2; for a shut-in injection well, its former injection rate at reservoir conditions, m³/d Well testing · Pressure measurements in producing reservoirs: barriers and accuracy well rate at reservoir conditions, from the fine-grid calculation, m³/d Simulation · Permeability upscaling for single-phase flow injection rate of the well at reservoir conditions, m³/d Simulation · Special topics in upscaling slope of the Mohr–Coulomb line: how many megapascals the strength grows for each megapascal of confining pressure, — Drilling · Bit selection and dull grading volumetric flow rate through the choke, m³/s Drilling · Blowout prevention equipment displacement per revolution: the volume of mud that passes through the motor in one revolution of the rotor, m³/rev Drilling · Deflection tools and downhole motors total rate of the well, m³/d Production · Multiple-zone completions: commingled and segregated production flow rate, usually at standard conditions, m³/d Production · Nodal analysis of the production system volumetric flow rate of the liquid at tubing conditions, m³/s Production · Nodal analysis of the production system flow rate, m³/d Production · Nodal analysis of the production system oil (liquid) rate at standard conditions, m³/d Production · Inflow performance relationship (IPR) oil rate at standard conditions, m³/s Production · Inflow performance relationship (IPR) oil rate at standard conditions at the bottomhole pressure p w f p_{wf} p w f , m³/d Production · Inflow performance relationship (IPR) volumetric flow rate of the liquid, m³/s Production · Chokes, surface pressure losses and well temperature liquid rate (oil and water) at standard conditions, STB/d Production · Chokes, surface pressure losses and well temperature operating rate of the base case, m³/d Production · Well performance sensitivity analysis volumetric flow rate through the pump at intake conditions, m³/s Production · Artificial lift: when it is needed and how to choose the method actual delivery of liquid, measured at the surface, m³/d Production · Sucker-rod pumping delivery of production at intake conditions, m³/d Production · Hydraulic pumps: piston and jet actual delivery at intake conditions, m³/d Production · Progressing cavity pumps and hybrid systems liquid flow rate, m³/d Production · Gas lift: principles and choice of operating conditions flow rate of liquid through these holes, m³/s Production · Perforating operations: gun conveyance and procedures flow rate at reservoir conditions, m³/s Production · Formation damage and damage skin current injection rate, m³/s Production · Acid systems and treatment design rate of acid into the interval, m³/s Production · Acid treatment of carbonates and special wells slope of the line: how much confinement strengthens the rock, — Production · Sand production: types, prediction and cost of the problem flow rate of the phase at the conditions of the vessel, m³/min Production · Oil treating: separators, dehydration, desalting and stabilisation water rate through the tank, m³/s Production · Produced water: composition, treatment and disposal injection rate at standard conditions, m³/d Production · Water injection systems current production, bbl/d Economics · Oil companies and investment Q Q Q quality factor of the rocks: the larger it is, the weaker the absorption; average values for a sedimentary section are tens to hundreds, — Geoscience · Seismic waves, acoustic impedance and reflections the quantity that will actually be recovered by the project from the date of the estimate to the end of production, t, m³ or bbl Geoscience · Classification of reserves and resources normalised resistivity ratio, — Logs and petrophysics · Resistivity ratio methods and movable oil underground withdrawal per unit of time, the denominator of VRR, m³/d Reservoir engineering · Why water is injected: pressure maintenance and oil displacement total rate through the block at reservoir conditions, m³/s Simulation · Permeability upscaling for single-phase flow rate between them in the fine-grid calculation, at reservoir conditions, m³/d Simulation · Permeability upscaling for single-phase flow pump rate, m³/s Drilling · How a well is drilled: the process and the people involved flow rate, m³/s Drilling · Circulating pressure losses flow rate of the pumps, m³/s Drilling · Bit hydraulics optimisation chosen flow rate, m³/s Drilling · Bit hydraulics optimisation flow rate of the mud through the motor, m³/s Drilling · Deflection tools and downhole motors force that the soil holds by friction and adhesion along the wall, kN Drilling · Offshore and subsea drilling flow rate of the liquid, m³/s Production · Progressing cavity pumps and hybrid systems oil plateau rate: how much oil the wells can give and the oil treatment unit can take, m³/d Production · Field development concepts: surface facilities oil plateau rate, m³/d Production · Field development concepts: surface facilities actual volume rate of gas at the pressure and temperature of the separator, m³/s Production · Oil treating: separators, dehydration, desalting and stabilisation production over the same period, million bbl Economics · Oil companies and investment annual production, million bbl/yr Economics · Oil companies and investment q 1 , q 2 q_1,\ q_2 q 1 , q 2 q b q_b q b q c q_c q c q cr q_{\text{cr}} q cr q i q_i q i injection rate at reservoir conditions, m³/d Reservoir engineering · Buckley–Leverett theory and the Welge method withdrawal by a well from cell i i i , m³/d Simulation · Pressure equation for single-phase flow withdrawal by a well from the cell at reservoir conditions, m³/d Simulation · Finite differences: from equations to computation withdrawal by a well at reservoir conditions (injection with a minus sign), m³/d Simulation · Solving systems of linear equations in simulators rate of zone i i i , m³/d Production · Multiple-zone completions: commingled and segregated production injection rate, into both wings together, m³/s Production · Fracture design: size and conductivity injection rate into well i i i , m³/d Production · Water injection systems initial flow rate, expressed as a volume per year (daily rate × 365), bbl per year (m³ per year, t per year) Economics · Annuities and discounted production the initial production rate, expressed as a volume per year, bbl a year Economics · Annual capital charge Q i Q_i Q i q j q_j q j rate of well j j j , m³/s Reservoir engineering · Superposition principle rate in step j j j q 0 = 0 q_0 = 0 q 0 = 0 , m³/s Reservoir engineering · Superposition principle rate of the j j j , thousand m³/d Well testing · Inflow at high rates: non-Darcy flow rate of flow period number j j j q 0 = 0 q_0 = 0 q 0 = 0 q n q_n q n , m³/d Well testing · Equivalent producing time and synthetic flowing time rates of all the wells of the block at standard conditions; if the block has injection wells, their injection, converted to reservoir conditions, is subtracted from the sum ∑ q j B \sum q_jB ∑ q j B , m³/s Well testing · Testing in a developed reservoir: Slider's method net withdrawal of the wells of the tank (production minus injection) at reservoir conditions, m³/d Well testing · Lumped multi-tank material balance model rate of the j j j , m³/s Production · Multilateral wells q max q_{\max} q m a x q m a x q_{max} q ma x q n q_n q n q o q_o q o q o , q w q_o,\ q_w q o , q w q s q_s q s q t q_t q t q , B q,\ B q , B rate at standard conditions and formation volume factor, m³/s, m³/m³ Reservoir engineering · Flow regimes rate at standard conditions and formation volume factor; q B qB q B , m³/s, m³/m³ Well testing · Dimensionless well solutions: skin, radius of investigation and units change of the rate at the wellhead at standard conditions, and formation volume factor, m³/s, m³/m³ Well testing · Diagnosis with the pressure derivative rate at standard conditions and formation volume factor, m³/s, m³/m³ Well testing · Diagnosis with the pressure derivative rate before shut-in at standard conditions and formation volume factor, m³/d, m³/m³ Well testing · Nonideal wellbore storage, well clean-up and changing skin q , B , μ q,\ B,\ \mu q , B , μ flow rate at standard conditions, formation volume factor, viscosity, m³/s, m³/m³, Pa·s Well testing · Partial penetration and well deviation rate at standard conditions, formation volume factor, viscosity, m³/s, m³/m³, Pa·s Well testing · Pressure drawdown analysis rate before shut-in at standard conditions, formation volume factor, viscosity, m³/s, m³/m³, Pa·s Well testing · Pressure build-up analysis change of the rate at the wellhead at standard conditions, formation volume factor (reservoir volume per unit of surface volume), viscosity, m³/s, m³/m³, Pa·s Well testing · Type-curve matching rate at standard conditions (after start-up or before shut-in), formation volume factor, viscosity, m³/s, m³/m³, Pa·s Well testing · Type-curve matching change of the rate at standard conditions, formation volume factor (reservoir volume per unit of surface volume), viscosity, m³/s, m³/m³, Pa·s Well testing · Diagnosis with the pressure derivative oil rate before shut-in at standard conditions, formation volume factor, and oil viscosity at reservoir conditions, m³/d, m³/m³, mPa·s Well testing · Comparing formation-tester, core and well-test data rate at standard conditions, formation volume factor, viscosity, m³/s, m³/m³, Pa·s Production · Inflow to a hydraulically fractured well q , B , μ , k , h q,\ B,\ \mu,\ k,\ h q , B , μ , k , h rate, formation volume factor, viscosity, permeability, thickness, m³/s, m³/m³, Pa·s, m², m Reservoir engineering · Superposition principle rate at standard conditions, formation volume factor, viscosity, permeability, thickness, m³/s, m³/m³, Pa·s, m², m Well testing · Dimensionless well solutions: skin, radius of investigation and units rate before shut-in, formation volume factor, viscosity, permeability, thickness, m³/s, m³/m³, Pa·s, m², m Well testing · Pressure build-up analysis as in the inflow formula, m³/s, m³/m³, Pa·s, m², m Well testing · Reservoir limit test rate before shut-in at standard conditions, formation volume factor, viscosity, permeability, thickness, m³/s, m³/m³, Pa·s, m², m Well testing · Testing in a developed reservoir: Slider's method q , B , μ , k , h , ϕ , c t q,\ B,\ \mu,\ k,\ h,\ \phi,\ c_t q , B , μ , k , h , ϕ , c t as in the line-source solution, m³/s, m³/m³, Pa·s, m², m, —, 1/Pa Reservoir engineering · Line-source solution and the pressure function rate, formation volume factor (reservoir volume per unit of surface volume), viscosity, permeability, thickness, porosity, total compressibility, m³/s, m³/m³, Pa·s, m², m, —, 1/Pa Well testing · Several boundaries: parallel faults and wedge-shaped blocks q ( t ) q(t) q ( t ) r r r depth of the root: how much deeper the base of the crust is under the mountains than under a plain with normal crust, km Geoscience · Structure and composition of the Earth rate of quartz precipitation per unit area of grain surface, mol/(cm²·s) Geoscience · Diagenesis: compaction, cementation and dissolution radius of the narrowest point of the pore channel, m Geoscience · Reservoir and seal equivalent radius of the channels, m Geoscience · Reservoir and seal distance of the point from the centre of the projection circle, mm on the drawing Geoscience · Stress, strain and structural analysis angle in the fault plane between the strike line and the direction of slip (rake), ° Geoscience · Faults correlation coefficient, from −1 to 1, — Logs and petrophysics · Log acquisition, processing and presentation distance from the electrode, m Logs and petrophysics · Resistivity logs: electrical and induction tools pressure ratio of adjacent stages, — Reservoir engineering · Separator calculations and optimum separator pressure radius of the channel; in a rock, the effective radius of the pore throat through which the meniscus passes, m Reservoir engineering · Capillary pressure and the transition zone distance from the well axis, r w ≤ r ≤ r e r_w \le r \le r_e r w ≤ r ≤ r e , m Well testing · Steady-state radial flow distance from the well axis, m Well testing · Inflow at high rates: non-Darcy flow ratio of the derivative at time t t t 1 < r < 2 1 < r < 2 1 < r < 2 , — Well testing · Semi-infinite systems: theory and test analysis distance from the well that creates the pulse to the observation well, m Well testing · Pressure measurements in producing reservoirs: barriers and accuracy mesh Fourier number : the time step in units of the time that the pressure needs to level out over one cell, — Simulation · Finite differences: from equations to computation mesh Fourier number η Δ t / Δ x 2 \eta\Delta t/\Delta x^2 η Δ t /Δ x 2 , — Simulation · Finite differences: from equations to computation distance from the axis of the well, m Simulation · Special topics in upscaling spread rate: the rig with its crew and all the services paid by the day, US$ thousand/d Drilling · Drilling time and cost spread rate, US$ thousand/d Drilling · Drilling time and cost radial clearance between the pipe body and the wall of the hole, ( D hole − D ) / 2 (D_{\text{hole}} - D)/2 ( D hole − D ) /2 , m Drilling · Drill string design radial clearance between the tubing and the casing, m Production · Completion string equipment ratio of the pressures downstream and upstream of the choke, but not less than the critical r c r_c r c , — Production · Chokes, surface pressure losses and well temperature radius of the dissolving front from the well axis, m Production · Acid systems and treatment design distance of the front from the well axis, m Production · Acid treatment of carbonates and special wells compression ratio of one stage: the ratio of the discharge and suction pressures, — Production · Gas processing and compression share of revenue taken by the payments levied on revenue (royalty), fraction Economics · Cash flow model of an oil and gas project real rate — the growth of purchasing power, fraction per year Economics · Interest and compounding real rate: the growth in purchasing power, fraction per year Economics · Inflation: nominal and real money share of revenue that goes to the royalty, fraction Economics · Unit costs per barrel payments on revenue (royalty, production tax) per unit of increase, fraction Economics · Petroleum fiscal systems and taxation royalty and other payments on revenue, share of revenue Economics · Petroleum fiscal systems and taxation share of revenue that goes to payments on revenue (royalty), fraction Economics · Sensitivity analysis and scenarios a possible result of the data, for example a positive or a negative answer, — Economics · Decision trees and the value of information the result received: a positive or a negative answer, — Economics · Decision trees and the value of information interest rate per year: the cost of the money put into the oil, fraction per year Economics · Market, financial and regulatory uncertainty R R R radius of the Earth, 6371 km, km Geoscience · Plate tectonics and sedimentary basins universal gas constant, 8.314 J/(mol·K), J/(mol·K) Geoscience · Source rocks, maturation and migration radius of the projection circle, mm Geoscience · Stress, strain and structural analysis radius of curvature of the neutral surface, m Geoscience · Folds, salt diapirs and their relationship to faults reflection coefficient : the ratio of the pressure amplitude in the reflected wave to that in the incident wave, — Geoscience · Seismic waves, acoustic impedance and reflections reflection coefficient of the boundary for a wave going down, — Geoscience · Seismic waves, acoustic impedance and reflections telemetry rate, bit/s Logs and petrophysics · Open-hole logging: why, how and when value of the curve, Ω·m Logs and petrophysics · Log acquisition, processing and presentation universal gas constant, 8.314 J/(mol·K), J/(mol·K) Logs and petrophysics · Spontaneous potential (SP) log ratio of the interval transit times, equal to V p / V s V_p/V_s V p / V s , — Logs and petrophysics · Sonic log electrical resistivity, Ω·m Logs and petrophysics · Resistivity logs: electrical and induction tools resistivity of the rock, Ω·m Logs and petrophysics · Resistivity logs: electrical and induction tools resistivity of the medium, Ω·m Logs and petrophysics · Resistivity logs: electrical and induction tools solution gas–oil ratio or producing gas–oil ratio — the volume of gas per volume of oil at standard conditions, m³/m³; scf/STB Reservoir engineering · Systems of units: SI, oilfield and metric oilfield gas constant, 8314 J/(kmol·K), J/(kmol·K) Reservoir engineering · Reservoir pressure and temperature universal gas constant, 8.314 J/(mol·K), J/(mol·K) Reservoir engineering · Phase behaviour: pure substances and binary mixtures gas–oil ratio: the standard volume of gas per 1 m³ of liquid, m³/m³ Reservoir engineering · Types of reservoir fluids universal gas constant, 0.008314 MPa·m³/(kmol·K), MPa·m³/(kmol·K) Reservoir engineering · Cubic equations of state producing gas–oil ratio (all the produced gas per cubic metre of oil), m³/m³ Reservoir engineering · Black oil model: solution gas–oil ratio and formation volume factors separator and stock-tank gas per 1 m³ of stable condensate, gas at 20 °C, m³/m³ Reservoir engineering · PVT correlations for oil and gas condensate total gas–oil ratio of the reservoir mixture: separator and stock-tank gas per 1 m³ of stock-tank oil, m³/m³ Reservoir engineering · Reservoir fluid sampling universal gas constant, 8.314, J/(mol·K) Reservoir engineering · Laboratory PVT tests universal gas constant, 8.3145 kPa·m³/(kmol·K), kPa·m³/(kmol·K) Reservoir engineering · Material balance for gas reservoirs instantaneous (current) gas–oil ratio: the ratio of the gas rate to the oil rate, both at standard conditions, m³/m³ Reservoir engineering · Performance prediction for solution gas drive reservoirs measured gas–oil ratio of the accumulation (the sum over the wells) on the date, m³/m³ Reservoir engineering · Performance prediction for solution gas drive reservoirs instantaneous (current) producing gas–oil ratio: all the produced gas per cubic metre of oil, m³/m³ Reservoir engineering · Why water is injected: pressure maintenance and oil displacement producing gas–oil ratio: the gas per cubic metre of oil at standard conditions (producing gas–oil ratio ), m³/m³ Reservoir engineering · Displacement of oil by gas universal gas constant, 8.314, J/(mol·K) Well testing · Inflow at high rates: non-Darcy flow producing gas–oil ratio, m³/m³ Simulation · Reservoir simulation in practice: case studies nominal breaking strength of the line according to the standard or certificate, kN Drilling · Drilling rig: power and hoisting systems rate of penetration , m/h Drilling · Drill bits: types and design rate of penetration at the mean weight of the step, m/s Drilling · Bit performance and cost per metre universal gas constant, 8.314 J/(mol·K), J/(mol·K) Drilling · Pore pressure and overburden pressure radius of curvature of the hole, m Drilling · Casing design universal gas constant, 8.314, J/(mol·K) Drilling · Water-based muds and clay chemistry the required ratio: the share of base oil in the liquid phase, fraction Drilling · Oil-based muds radius of curvature of the axis of the well, m Drilling · Directional wells: applications and profile radius of the build arc, m Drilling · Directional wells: applications and profile useful rate of the channel, bit/s Drilling · Measurement while drilling dimensionless resistance to inflow (the analogue of ln ( r e / r w ) + S \ln(r_e/r_w) + S ln ( r e / r w ) + S , — Production · Horizontal wells radius of the tunnel ends, m Production · Effect of completion on inflow producing gas–oil ratio, m³/m³ Production · Artificial lift: when it is needed and how to choose the method ratio of the areas of the nozzle and of the mixing chamber, — Production · Hydraulic pumps: piston and jet universal gas constant, 8.314 J/(mol·K), J/(mol·K) Production · Gas lift: principles and choice of operating conditions ratio of the seat area to the bellows area; for unloading valves it is usually a few hundredths, — Production · Unloading a gas lift well: valves and mandrels ratio of the seat area to the bellows area, — Production · Unloading a gas lift well: valves and mandrels return permeability of the whole sample, fraction Production · Sources of formation damage the share of the conductivity retained after the effect of the fracturing fluid (retained conductivity), — Production · Fracture design: size and conductivity universal gas constant, 8.314, J/(mol·K) Production · Gas processing and compression reserves at the end of the year, million bbl Economics · Oil companies and investment reserves over which the asset is depreciated (the basis follows the company's accounting policy: proved, or proved plus probable; for development costs, often the developed reserves), million bbl Economics · Valuation methods: book value and market value risk tolerance , US$ million Economics · Expected monetary value and preference theory risk tolerance, US$ million Economics · Expected monetary value and preference theory R ∞ R_\infty R ∞ r 0 r_0 r 0 R 0 R_0 R 0 r 1 , r 2 r_1,\ r_2 r 1 , r 2 R 1 , R 2 R_1,\ R_2 R 1 , R 2 r d r_d r d r e r_e r e r e , r w r_e,\ r_w r e , r w r e , r w , S r_e,\ r_w,\ S r e , r w , S radius of the drainage area, radius of the well, skin factor (how much the zone right around the well helps or hinders flow), m, m, — Reservoir engineering · Performance prediction for solution gas drive reservoirs radius of the drainage area, radius of the well, skin factor, m, m, — Well testing · Skin factor radius of the drainage area, well radius and the current skin, m, m, — Production · Acid systems and treatment design r f r_f r f r i r_i r i R k R_k R k r p r_p r p R p R_p R p R s R_s R s solution gas–oil ratio of the oil at pressure p p p , m³/m³ Reservoir engineering · Black oil model: solution gas–oil ratio and formation volume factors solution gas–oil ratio, m³/m³ Reservoir engineering · Black oil model: solution gas–oil ratio and formation volume factors solution gas–oil ratio of oil saturated at pressure p p p , scf/STB Reservoir engineering · PVT correlations for oil and gas condensate solution gas–oil ratio of the oil at pressure p p p , scf/STB Reservoir engineering · Oil viscosity and interfacial tension solution gas–oil ratio of the oil at the current pressure: the dissolved gas, m³/m³ Reservoir engineering · Performance prediction for solution gas drive reservoirs solution gas–oil ratio at the current average reservoir pressure, m³/m³ Reservoir engineering · Why water is injected: pressure maintenance and oil displacement solution gas–oil ratio of the oil at reservoir pressure, m³/m³ Reservoir engineering · Displacement of oil by gas solution gas–oil ratio (the gas dissolved in each cubic metre of oil) at the current reservoir pressure, m³/m³ Well testing · Well inflow: the well performance diagram solution gas–oil ratio of the oil (the gas dissolved in a unit volume of oil) at the pressure in the cell, m³/m³ Simulation · Types of reservoir simulation model solution gas–oil ratio: standard cubic metres of gas dissolved in 1 m³ of stock-tank oil, m³/m³ Simulation · Building a simulation model: input data and results solution gas–oil ratio of the oil at intake pressure and temperature, m³/m³ Production · Artificial lift: when it is needed and how to choose the method solution gas–oil ratio of the oil at the pressure and the temperature of the intake, m³/m³ Production · Electric submersible pumps (ESP) R t R_t R t resistivity of the rock at water saturation S w S_w S w , Ω·m Logs and petrophysics · Archie's equation and saturation of clean reservoirs resistivity of the uninvaded part of the formation (after corrections), Ω·m Logs and petrophysics · Archie's equation and saturation of clean reservoirs resistivity of the uninvaded part of the bed: the reading of the deep sonde (a tool that looks far into the rock) after corrections, Ω·m Logs and petrophysics · Determining formation water resistivity resistivity of the uninvaded part of the bed, Ω·m Logs and petrophysics · Determining formation water resistivity resistivity of the uninvaded part of the formation (with corrections), Ω·m Logs and petrophysics · Resistivity–porosity crossplots resistivity of the uninvaded part of the formation, Ω·m Logs and petrophysics · Resistivity ratio methods and movable oil resistivity of the uninvaded part of the bed (the part that the mud filtrate has not reached), Ω·m Logs and petrophysics · Water saturation in shaly sands resistivity of the bed along the bedding, Ω·m Logs and petrophysics · Water saturation in shaly sands formation resistivity, Ω·m Logs and petrophysics · Interpretation charts: how to read them resistivity of the uninvaded part of the formation, beyond the invaded zone (the zone around the well that mud filtrate has entered), Ω·m Reservoir engineering · Fluid saturation revenue of the period, US$ million Economics · Project cash flow revenue of year t t t , US$ million Economics · Cash flow model of an oil and gas project value of the year's production: production multiplied by price, US$ million Economics · Licences and contracts for subsoil use the contractor's R-factor at the start of year t t t Licences and contracts for subsoil use also calls R t R_t R t , — Economics · Petroleum fiscal systems and taxation r w r_w r w radius of the well, m Reservoir engineering · Rock permeability wellbore radius, m Reservoir engineering · Line-source solution and the pressure function well radius, m Well testing · Steady-state radial flow actual wellbore radius, m Well testing · Skin factor wellbore radius, m Well testing · Pressure drawdown analysis radius of the hole, m Well testing · Supercharging and permeability from formation-tester pretests wellbore radius, m Simulation · Grids in reservoir simulation models wellbore radius, m Production · Inflow performance relationship (IPR) wellbore radius (the radius of the bit), m Production · Effect of completion on inflow well radius, m Production · Formation damage and damage skin radius of the open hole, m Production · Sources of formation damage radius of the wellbore, m Production · Hydraulic fracturing: purpose and well selection R w R_w R w r w , S r_w,\ S r w , S r w ′ r_w' r w ′ r , R r,\ R r , R Re \text{Re} Re R R R \mathrm{RRR} RRR s s s how many corners, on average, a tetrahedron shares with neighbouring tetrahedra (from 0 to 4), — Geoscience · Minerals and rocks the same in decimal logarithms — the residual standard deviation of the regression, — Geoscience · Reservoir quality: geological controls on porosity and permeability vertical separation of the bed: the vertical distance between the parts of one bed in the two walls. In a vertical well it is the thickness of the missing interval (for a normal fault) or the repeated interval (for a reverse fault), m Geoscience · Faults average spacing of the set, m Geoscience · Fractures and naturally fractured reservoirs standard deviation (SD), also called the root-mean-square deviation, units of the quantity Geoscience · Descriptive statistics in geology standard deviation, units of the quantity Geoscience · Descriptive statistics in geology standard deviation of the data, units of the quantity Geoscience · Distributions and sample size standard deviation of the results of the trials, units of the result Geoscience · Probabilistic volumetrics by Monte Carlo simulation span of the tool, the distance between the receivers, m Logs and petrophysics · Sonic log variable of the transform (conjugate to t D t_D t D , — Reservoir engineering · Unsteady-state water influx: the van Everdingen–Hurst method variable of the Laplace transform, which corresponds to the dimensionless time t D t_D t D , — Well testing · Wellbore storage root-mean-square deviation of the points from the line, ∑ e i 2 / ( n − 2 ) \sqrt{\sum e_i^2/(n - 2)} ∑ e i 2 / ( n − 2 ) e i e_i e i n n n , Pa Well testing · Pressure measurement with the wireline formation tester standard deviation of the logarithms of the ratios, — Well testing · Comparing formation-tester, core and well-test data scatter of a valid point about the line: the repeatability and the depth errors, known from other lines of the survey or from repeat pretests, Pa Well testing · Forced-gradient technique and multi-well analysis Laplace transform variable, 1/d Well testing · Pressure measurements in producing reservoirs: barriers and accuracy length along the hole, measured upward, m Drilling · Drill string design gap between the ring pressed to two cones and the gauge cutting structure of the third cone, mm Drilling · Bit selection and dull grading an auxiliary quantity, — Drilling · Casing design slippage coefficient: how much liquid flows back for each megapascal of pressure drop, m³/(d·MPa) Production · Progressing cavity pumps and hybrid systems the share of world supply that has left the market, fraction Economics · The oil industry in history: demand, supply and prices the state's share of profit oil, fraction Economics · Licences and contracts for subsoil use share of in-country value in the works and services of the calendar year, fraction Economics · State regulation of field development detection rate P ( + ∣ H ) P(+\mid H) P ( + ∣ H ) , fraction Economics · Decision trees and the value of information the share of the cost of the well that the partner pays; s − w s - w s − w s = 1 s = 1 s = 1 , fraction Economics · Risk reduction and diversification S S S thickness of the sediments that have filled the basin up to the former water level, km Geoscience · Structure and composition of the Earth slope of the water surface, m/m Geoscience · Primary sedimentary structures stretch, — Geoscience · Stress, strain and structural analysis shortening of the section — a length; the stretch ratio l / l 0 l/l_0 l / l 0 lesson on strain here equals 1 − ε 1 - \varepsilon 1 − ε , m Geoscience · Practical structural geology shortening, m Geoscience · Practical structural geology skin factor, — Reservoir engineering · Line-source solution and the pressure function skin factor : S > 0 S > 0 S > 0 S < 0 S < 0 S < 0 , — Well testing · Steady-state radial flow skin factor, if the near-wellbore zone is altered, — Well testing · Steady-state radial flow skin factor , — Well testing · Pseudo-steady-state flow and the shape factor measured (total) skin factor of the well, — Well testing · Skin factor skin factor from the same test, — Well testing · Skin factor skin from the well test (late radial flow), counted over the whole thickness, — Well testing · Partial penetration and well deviation skin from the well test, counted over the thickness h h h , — Well testing · Partial penetration and well deviation skin that does not depend on the rate: damage to the near-wellbore zone, geometry of penetration, perforation, — Well testing · Inflow at high rates: non-Darcy flow skin factor of the real well; the image has no skin, — Well testing · A sealing fault near the well: the method of images skin of the well: it enters once, because it refers to the real rate, — Well testing · Semi-infinite systems: theory and test analysis skin of the well under test, — Well testing · Testing in a developed reservoir: Slider's method tool storage: the volume of liquid in the line and the chamber multiplied by its compressibility, cm³/MPa Well testing · Pressure measurement with the wireline formation tester storage capacity of a cell (the same for all cells), m³/MPa Simulation · Solving systems of linear equations in simulators damage skin around the horizontal wellbore, — Production · Horizontal wells skin factor — the additional resistance of the near-wellbore zone (see Skin factor ), — Production · Inflow performance relationship (IPR) bean diameter in sixty-fourths of an inch, 1/64″ Production · Chokes, surface pressure losses and well temperature skin from the well test, for the whole thickness, — Production · Effect of completion on inflow length of the stroke of the polished rod, m Production · Sucker-rod pumping fall of the pressure of the production from the intake to the inlet of the mixing chamber, in the same fractions, — Production · Hydraulic pumps: piston and jet content of chloride salts in the oil, mg/dm³ Production · Oil treating: separators, dehydration, desalting and stabilisation salvage value — what the asset can be sold for at the end of its life, minus disposal costs (often taken as 0), US$ million Economics · Valuation methods: book value and market value residual value at the end of the life: the price of sale or of moving to another site, less dismantling, US$ million Economics · Annual capital charge S 0 S_0 S 0 S 1 S_1 S 1 s c s_c s c S d S_d S d S f S_f S f S i S_i S i s j s_j s j S j S_j S j s k s_k s k S n S_n S n S o , S w S_o,\ S_w S o , S w S o , S w , S g S_o,\ S_w,\ S_g S o , S w , S g S o r S_{or} S or S p p S_{pp} S pp S w S_w S w mean initial water saturation of the reservoir; 1 − S w 1 - S_w 1 − S w S o S_o S o , fraction Geoscience · Volumetric estimation of hydrocarbons in place water saturation of the uninvaded formation, fraction Logs and petrophysics · Borehole environment: invaded zone and mudcake water saturation of the bed, fraction Logs and petrophysics · Log interpretation workflow water saturation of the uninvaded formation (from R t R_t R t R w R_w R w , fraction Logs and petrophysics · Microresistivity tools and flushed-zone resistivity water saturation, fraction Logs and petrophysics · Archie's equation and saturation of clean reservoirs water saturation of the uninvaded part of the formation, fraction Logs and petrophysics · Archie's equation and saturation of clean reservoirs its true water saturation, fraction Logs and petrophysics · Determining formation water resistivity water saturation of the line, fraction Logs and petrophysics · Resistivity–porosity crossplots water saturation of the sandy layers, fraction Logs and petrophysics · Water saturation in shaly sands effective water saturation, fraction Logs and petrophysics · Water saturation in shaly sands water saturation of the effective pore volume, fraction Logs and petrophysics · Water saturation in shaly sands average water saturation (see Fluid saturation ), fraction Reservoir engineering · Porosity connate water saturation, fraction Reservoir engineering · Material balance for gas reservoirs water saturation in the section x x x t t t , — Reservoir engineering · Buckley–Leverett theory and the Welge method water saturation, the unknown, — Simulation · Two-phase flow equations S w e S_{we} S w e S w i , S o r S_{wi},\ S_{or} S w i , S or S w i r r S_{wirr} S w i r r S i O 2 \mathrm{SiO_2} Si O 2 t t t age of this boundary from the reversal time scale, million years Geoscience · Plate tectonics and sedimentary basins time after stretching, million years Geoscience · Plate tectonics and sedimentary basins age — the time since the system closed, years Geoscience · Stratigraphy and geologic time age, years Geoscience · Stratigraphy and geologic time thickness of one cross-set, measured vertically, m Geoscience · Continental environments: aeolian and fluvial duration of the advance, years Geoscience · Coastal, shallow-marine and deep-marine environments time, years Geoscience · Carbonate sediments, environments and carbonate porosity throw (vertical offset), m Geoscience · Faults greatest throw of a fault, m Geoscience · Faults throw of the fault at this point, m Geoscience · Faults two-way time to it, s Geoscience · Geophysical exploration methods time from the centre of the wavelet, s Geoscience · Seismic waves, acoustic impedance and reflections travel time along the whole path; for a reflected wave, the two-way time, s Geoscience · Seismic waves, acoustic impedance and reflections two-way time of the horizon, s Geoscience · Seismic interpretation two-way time from the top of the unit, s Geoscience · Seismic interpretation throw (vertical amplitude), m Geoscience · Cross-sections from maps, map combination and faults on maps throw at the place where the contour ends in the hanging wall, m Geoscience · Cross-sections from maps, map combination and faults on maps Student's coefficient (a table value) for the chosen confidence probability and N − 1 N - 1 N − 1 , — Geoscience · Distributions and sample size Student's coefficient; about 2 at a probability of 95% and more than thirty samples, — Geoscience · Distributions and sample size filtration time, s Logs and petrophysics · Borehole environment: invaded zone and mudcake travel time from the transmitter to the receiver, µs Logs and petrophysics · Sonic log one-way travel time of the wave through the interval; the two-way time is 2 t 2t 2 t , µs Logs and petrophysics · Sonic log time from the initial moment, years Reservoir engineering · Reservoir engineering: tasks across the life of a field temperature on the Celsius or Fahrenheit scale, °C, °F Reservoir engineering · Systems of units: SI, oilfield and metric oilfield the new unknown, t = Z + c 2 / 3 t = Z + c_2/3 t = Z + c 2 /3 , — Reservoir engineering · Cubic equations of state time since the pressure at the contact started to fall, s Reservoir engineering · Aquifer models: water influx time, d Reservoir engineering · Aquifer models: water influx time since the pressure drop, s Reservoir engineering · Unsteady-state water influx: the van Everdingen–Hurst method time of production at a constant flow rate since start-up or the last change of flow rate, s Well testing · Pseudo-steady-state flow and the shape factor time since the start of production (since shut-in, for a pressure build-up), s Well testing · Partial penetration and well deviation time since the well was started, days Well testing · Water and gas coning time since the rate change, s Well testing · Well testing: purposes and types of test time after start-up, s Well testing · Well testing: purposes and types of test time since start-up of the well, s Well testing · Dimensionless well solutions: skin, radius of investigation and units time since start-up, s Well testing · Dimensionless well solutions: skin, radius of investigation and units time, s Well testing · Wellbore storage time since start-up or shut-in (after shut-in, Δ t \Delta t Δ t , s Well testing · Wellbore storage time since start-up or shut-in (for a build-up, Δ t \Delta t Δ t , s Well testing · Type-curve matching time since start-up or shut-in, s Well testing · Diagnosis with the pressure derivative time since the start of production at a constant rate, s Well testing · Nonideal wellbore storage, well clean-up and changing skin duration of production at a constant rate, h Well testing · Reservoir limit test Student's coefficient for n − 1 n - 1 n − 1 n n n , — Well testing · Comparing formation-tester, core and well-test data time since the start of withdrawal, s Well testing · Pressure measurements in producing reservoirs: barriers and accuracy time since the start of withdrawal, d Simulation · What a reservoir simulation model is and why it is needed time of drilling with the bit on the bottom, h Drilling · Bit selection and dull grading time of drilling with the bit, h Drilling · Bit performance and cost per metre wall thickness (nominal), m Drilling · Casing: purpose, types, properties and standards the time of the test: 30 min, or the moment when the sample dehydrated and gas started to go through the filter, min Drilling · Oilwell cements and additives time from the start of the test, min Drilling · Field testing of drilling fluids duration of the test, s Drilling · Field testing of drilling fluids time to send the message, s Drilling · Measurement while drilling time the well has been producing, s Production · Chokes, surface pressure losses and well temperature time from the pulse to the arrival of the echo from the level, s Production · Sucker-rod pumping average temperature of the conductor along the well, °C Production · Electric submersible pumps (ESP) time since the well started at a constant rate, s Production · Inflow to a hydraulically fractured well average retention time of the phase in the vessel, min Production · Oil treating: separators, dehydration, desalting and stabilisation time from the origin to the payment, years Economics · Discounting and present value time from the valuation date to the flow, years Economics · Choosing the discount rate time from the origin, which coincides with the base year of the constant prices, years Economics · Inflation: nominal and real money number of the project year; the first year is the year of the first costs that still depend on the decision, — Economics · Cumulative cash flow and payback period time from the origin to the moment of the flow, years Economics · Net present value (NPV) time from the origin to the flow, years Economics · Internal rate of return (IRR) number of the year from the time origin (in the examples, the middle of year 1, with the flows in the middle of the year), — Economics · The state and the subsoil: ownership of resources number of the year from the start of counting, — Economics · Petroleum fiscal systems and taxation time from the time origin to the middle of the production year, years Economics · Geological and technical uncertainty of a project T T T wave period, s Geoscience · Primary sedimentary structures temperature, °C Geoscience · Diagenesis: compaction, cementation and dissolution absolute temperature, K Geoscience · Source rocks, maturation and migration characteristic generation temperature, K Geoscience · Source rocks, maturation and migration tensile strength of the rock (a positive number), MPa Geoscience · Fractures and naturally fractured reservoirs joints and normal faults, — Geoscience · Structural styles and tectonic history transmissibility of the baffle: the flow rate through it per unit of pressure difference, m³/(s·Pa) Geoscience · Reservoir architecture and performance reservoir temperature, absolute (T [ K ] = t [ ∘ C ] + 273.15 T[\text{K}] = t[{}^{\circ}\text{C}] + 273.15 T [ K ] = t [ ∘ C ] + 273.15 , K Geoscience · Volumetric estimation of hydrocarbons in place absolute temperature, K Logs and petrophysics · Spontaneous potential (SP) log absolute temperature — in kelvins or degrees Rankine, K, °R Reservoir engineering · Systems of units: SI, oilfield and metric oilfield temperature at which p s p_s p s T b ≤ T ≤ T c T_b \le T \le T_c T b ≤ T ≤ T c , K Reservoir engineering · Phase behaviour: pure substances and binary mixtures absolute temperature, K Reservoir engineering · Phase behaviour: pure substances and binary mixtures absolute temperature, T = t [ ∘ C ] + 273.15 T = t\,[{}^{\circ}\text{C}] + 273.15 T = t [ ∘ C ] + 273.15 , K Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) absolute temperature in degrees Rankine, T [ ∘ R ] = 1.8 T [ K ] T\,[{}^{\circ}\text{R}] = 1.8\,T\,[\text{K}] T [ ∘ R ] = 1.8 T [ K ] , °R Reservoir engineering · Gas formation volume factor, compressibility and viscosity reservoir temperature, °F Reservoir engineering · Density and compressibility of reservoir oil temperature, °F Reservoir engineering · Oil viscosity and interfacial tension absolute temperature of the system, °R Reservoir engineering · Equilibrium ratios: correlations and equations of state temperature of the test, K Reservoir engineering · Laboratory PVT tests reservoir temperature, K Well testing · Steady-state radial flow temperature of the test, K Well testing · Inflow at high rates: non-Darcy flow equivalent time up to which the build-up must reproduce the drawdown, h Well testing · Effect of producing time on build-up analysis transmissibility of the barrier, 0.0853 k b A / ( μ b ) 0.0853\,k_bA/(\mu b) 0.0853 k b A / ( μ b ) A A A , m³/(d·MPa) Well testing · Pressure measurements in producing reservoirs: barriers and accuracy transmissibility of the fault between the block and its neighbour, m³/(d·MPa) Well testing · Lumped multi-tank material balance model absolute temperature: T [ K ] = t [ ∘ C ] + 273.15 T\,[\text{K}] = t\,[{}^{\circ}\text{C}] + 273.15 T [ K ] = t [ ∘ C ] + 273.15 , K Simulation · Types of reservoir simulation model days of work on the well according to the time estimate, d Drilling · Drilling time and cost tensile load in the pipe at this depth, N Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe average absolute temperature of the column, K Drilling · Pore pressure and overburden pressure tensile strength of the rock; zero for a fractured rock, MPa Drilling · Fracture gradient and leak-off testing absolute temperature, K Drilling · Water-based muds and clay chemistry tension in the line above the seal — the weight indicator reading, N Production · Wireline operations period of evaluation, yr Production · Acid treatment of carbonates and special wells tensile strength of the rock; zero for a wall that already has fractures, and after the first breakdown, MPa Production · Rock mechanics for hydraulic fracturing gas temperature, K Production · Gas processing and compression time until the flow rate falls to the economic limit q lim q_\text{lim} q lim T = ln ( q i / q lim ) / D T = \ln(q_i/q_\text{lim})/D T = ln ( q i / q lim ) / D , years Economics · Annuities and discounted production income tax rate; interest on debt reduces the taxable profit, fraction Economics · Choosing the discount rate time of the last flow of the project, including abandonment (closing the field down), years Economics · Net present value (NPV) income tax rate, fraction Economics · Unit costs per barrel the time the well works until its economic limit, the lowest rate at which it still pays to produce (here not the tax rate), years Economics · Annual capital charge time of the last flow of the project, including abandonment, years Economics · Internal rate of return (IRR) number of periods from the first flow to the last, years Economics · Internal rate of return (IRR) the rate of the income tax, fraction Economics · Petroleum fiscal systems and taxation time to delivery, years Economics · Market, financial and regulatory uncertainty T 0 T_0 T 0 T 1 T_1 T 1 T 1 , T 2 T_1,\ T_2 T 1 , T 2 temperature at the start of cementation and the present (or final) one, °C Geoscience · Diagenesis: compaction, cementation and dissolution temperatures, °C Logs and petrophysics · Formation water and formation temperature absolute temperatures of the reference conditions, K or °R Reservoir engineering · Systems of units: SI, oilfield and metric oilfield temperatures, °C Reservoir engineering · Density and compressibility of reservoir oil absolute temperatures, K Drilling · Well control: primary barrier and kick indicators temperature upstream and downstream of the choke, °C Production · Chokes, surface pressure losses and well temperature absolute suction and discharge temperature, K Production · Gas processing and compression T bh ( Δ t ) T_{\text{bh}}(\Delta t) T bh ( Δ t ) t B T t_{BT} t B T t c t_c t c t D t_D t D dimensionless time based on the wellbore radius, — Reservoir engineering · Line-source solution and the pressure function dimensionless time of the aquifer, — Reservoir engineering · Aquifer models: water influx dimensionless time of the aquifer, k t / ( ϕ μ w c t r o 2 ) kt/(\phi\mu_wc_tr_o^2) k t / ( ϕ μ w c t r o 2 ) , — Reservoir engineering · Unsteady-state water influx: the van Everdingen–Hurst method dimensionless time, referred to the length of the strip, — Reservoir engineering · Unsteady-state water influx: the van Everdingen–Hurst method dimensionless time of the aquifer, as in the van Everdingen–Hurst method, — Reservoir engineering · Simplified water influx models: Fetkovich and Carter–Tracy dimensionless time k h t / ( ϕ μ c t r w 2 ) k_h t/(\phi\mu c_t r_w^2) k h t / ( ϕ μ c t r w 2 ) , — Well testing · Partial penetration and well deviation dimensionless time of the start of the line, k t / ( ϕ μ c t r w 2 ) kt/(\phi\mu c_tr_w^2) k t / ( ϕ μ c t r w 2 ) , — Well testing · Wellbore storage dimensionless time k t / ( ϕ μ c t r w 2 ) kt/(\phi\mu c_tr_w^2) k t / ( ϕ μ c t r w 2 ) ln t D \ln t_D ln t D ln t \ln t ln t t D t_D t D t t t , — Well testing · Diagnosis with the pressure derivative dimensionless time k t / ( ϕ μ c t r w 2 ) kt/(\phi\mu c_tr_w^2) k t / ( ϕ μ c t r w 2 ) , — Well testing · A sealing fault near the well: the method of images dimensionless time, — Production · Chokes, surface pressure losses and well temperature t D A t_{DA} t D A t k t_k t k t n t_n t n t p t_p t p t pb t_{\text{pb}} t pb T res T_{\text{res}} T res t x t_x t x time in which the front covers the distance L L L ϕ Δ S L / u t \phi\,\Delta S\,L/u_t ϕ Δ S L / u t , s Reservoir engineering · Segregated flow and gravity displacement intersection time of the extensions of the first and second lines, s Well testing · A sealing fault near the well: the method of images time at which the line of the open channel (slope m L m_L m L 2 m L 2m_L 2 m L Δ p \Delta p Δ p t \sqrt t t , s Well testing · Semi-infinite systems: theory and test analysis time for the flow to cross the cell length L L L ϕ Δ S L / u \phi\,\Delta S\,L/u ϕ Δ S L / u , s Simulation · Two-phase upscaling: pseudo-functions T ( z ) T(z) T ( z ) T O C TOC T O C u u u random number, uniformly distributed between 0 and 1, — Geoscience · Probabilistic volumetrics by Monte Carlo simulation random number between 0 and 1, — Geoscience · Probabilistic volumetrics by Monte Carlo simulation filtration velocity towards the well: the flow rate through a unit area of the cylindrical surface, m/s Reservoir engineering · Diffusivity equation Darcy velocity through the fault: the flow rate at reservoir conditions per unit area of the zone, m/s Well testing · Partially communicating faults crossflow velocity at the boundary between the units: the share of the withdrawal that comes from the tight unit, divided by the area, m/s Well testing · Pressure measurements in producing reservoirs: barriers and accuracy Darcy velocity (the rate per unit area) at the distance r r r , m/d Simulation · Special topics in upscaling speed at which the tunnel deepens, m/s Production · Shaped-charge perforating natural logarithm of the dimensionless conductivity, — Production · Hydraulic fracturing: purpose and well selection water cut at time t t t , — Production · Field development concepts: surface facilities uptime factor: the fraction of calendar time during which the facilities operate, fraction Economics · Cash flow model of an oil and gas project the uplift on the carried-forward negative balance, which sets the threshold return, fraction per year Economics · Petroleum fiscal systems and taxation U U U u 1 , u 2 u_1,\ u_2 u 1 , u 2 u t u_t u t v v v half-rate — the speed at which the sea floor on one side moves away from the ridge axis, mm/yr = km/million years Geoscience · Plate tectonics and sedimentary basins speed of the point relative to the neighbouring plate, km/million years = mm/yr Geoscience · Plate tectonics and sedimentary basins rate of shoreline advance, m/yr Geoscience · Coastal, shallow-marine and deep-marine environments rate of penetration, m/h Logs and petrophysics · Open-hole logging: why, how and when rate of penetration at that time, m/h Logs and petrophysics · Log acquisition, processing and presentation logging speed, m/s Logs and petrophysics · Gamma ray log and natural gamma ray spectrometry Darcy velocity (flow rate per unit area), m/s Reservoir engineering · Oil viscosity and interfacial tension flow velocity (the flow rate divided by the area), m/s Reservoir engineering · Rock permeability Darcy velocity: the flow rate per unit cross-sectional area (not the velocity in the pores), m/s Well testing · Inflow at high rates: non-Darcy flow velocity of the front — the Darcy velocity divided by the porosity, m/s Simulation · Grids in reservoir simulation models average velocity of the flow: the flow rate divided by the cross-sectional area, m/s Drilling · Drilling fluid rheology and flow regimes average velocity of the flow, m/s Drilling · Drilling fluid rheology and flow regimes average velocity in the annulus, m/s Drilling · Drilling fluid rheology and flow regimes average velocity in the pipe, Q Q Q , m/s Drilling · Circulating pressure losses average velocity in the pipe or in the annulus, m/s Drilling · Circulating pressure losses mean velocity of the liquid in the tubing, m/s Production · Nodal analysis of the production system average speed of sound in the gas of the annulus, m/s Production · Sucker-rod pumping speed of an element of the jet, m/s Production · Shaped-charge perforating net income per cubic metre of extra oil, US$/m³ Production · Acid treatments: principle, economics and candidate selection average velocity of the fluid: the rate divided by the area of the cross-section, m/s Production · Fracturing fluids and tip-screenout fracturing settling (or rising) velocity of the droplet relative to the liquid, m/s Production · Oil treating: separators, dehydration, desalting and stabilisation variable costs, $/bbl Economics · Cash flow model of an oil and gas project V V V full opening rate: the sum of the half-rates of the two sides, mm/yr Geoscience · Plate tectonics and sedimentary basins recoverable volume of the discovery, if there is an accumulation, million m³ or million bbl Geoscience · Geological risk and chance of success exaggeration factor: how many times the vertical scale is larger than the horizontal one, — Geoscience · Stress, strain and structural analysis speed of the wave in the rock, m/s Geoscience · Seismic waves, acoustic impedance and reflections P-wave speed in the layer, m/s Geoscience · Seismic waves, acoustic impedance and reflections velocity in the overburden above the boundary (constant), m/s Geoscience · Seismic acquisition and processing velocity (constant), m/s Geoscience · Seismic acquisition and processing average velocity down to the boundary, m/s Geoscience · Seismic acquisition and processing volume of filtrate that has passed through the cake in time t t t , m³ Logs and petrophysics · Borehole environment: invaded zone and mudcake velocity of the wave in the rock, m/s Logs and petrophysics · Sonic log volume of the gas, m³ Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) volume of a given amount of gas, m³ Reservoir engineering · Gas formation volume factor, compressibility and viscosity total volume of the phase, m³ Reservoir engineering · Cubic equations of state volume of a given portion of oil (composition unchanged), m³ Reservoir engineering · Density and compressibility of reservoir oil mole fraction of the gas phase: how many moles out of each mole of the mixture ended up in the gas (not a volume), fraction Reservoir engineering · Vapour–liquid equilibrium mole fraction of the gas phase, — Reservoir engineering · Vapour–liquid equilibrium pumped volume, L Reservoir engineering · Reservoir fluid sampling the volume considered, m³ Reservoir engineering · Rock compressibility and the effect of stress on core properties underground withdrawal (withdrawal at reservoir conditions), m³/d Well testing · Well inflow: the well performance diagram the whole withdrawn volume q B t qBt q B t , m³ Well testing · Dimensionless well solutions: skin, radius of investigation and units rock volume of the accumulation, km²·m = million m³, million m³ Well testing · Perched and tilted contacts, trapped water volume of the block, m³ Simulation · Permeability upscaling for single-phase flow volume of mud that must be added, m³ Drilling · Well control: primary barrier and kick indicators the required volume of slurry (from the cementing design), m³ Drilling · Oilwell cements and additives volume of filtrate that has passed through the cake: V 30 − V s p V_{30} - V_{sp} V 30 − V s p , m³ Drilling · Field testing of drilling fluids volume of the mud, m³ Drilling · Oil-based muds displacement per revolution: the volume displaced in one turn of the rotor, m³ Production · Progressing cavity pumps and hybrid systems displacement per revolution of the pump, m³ Production · Progressing cavity pumps and hybrid systems volume of the main acid, m³ Production · Acid systems and treatment design volume of acid that has reacted in the fracture, m³ Production · Acid treatment of carbonates and special wells volume of filtrate by the time t t t , m³ (in the test, cm³) Production · Fracturing fluids and tip-screenout fracturing volume occupied by the phase in the working part of the vessel, m³ Production · Oil treating: separators, dehydration, desalting and stabilisation volume of gas at 20 °C and 101.325 kPa (Systems of units: SI, oilfield and metric oilfield ), m³ Economics · State regulation of field development gas that would otherwise be flared, per year, thousand m³ a year Economics · State regulation of field development value of the discovery at the date of the decision: the NPV of its development, not counting the cost of the exploration well, US$ million Economics · Expected monetary value and preference theory value of the discovery at the date of the decision: the NPV of its development, not counting the cost of the well, US$ million Economics · Decision trees and the value of information V 1 V_1 V 1 V 1 , V 2 V_1,\ V_2 V 1 , V 2 compressional wave velocities in the crust and in the upper mantle, km/s Geoscience · Structure and composition of the Earth interval velocities of the upper and the lower layer, m/s Geoscience · Seismic interpretation volume fractions of the two minerals in the rock, fraction Logs and petrophysics · Lithology from the photoelectric factor and spectral gamma ray volume of the same amount of gas at conditions 1 and 2, m³, ft³ Reservoir engineering · Systems of units: SI, oilfield and metric oilfield volumes of the sample at pressures p 1 > p 2 p_1 > p_2 p 1 > p 2 , cm³ Reservoir engineering · Laboratory PVT tests pore volumes of the units in the area drained by the wells of the site, m³ Well testing · Pressure measurements in producing reservoirs: barriers and accuracy pore volumes of the permeable and the tight unit, m³ Well testing · Pressure measurements in producing reservoirs: barriers and accuracy volume of the gas in states 1 and 2, m³ Drilling · Well control: primary barrier and kick indicators V ann V_{\text{ann}} V ann V b V_b V b V g V_g V g v i v_i v i V i V_i V i interval velocity of the compressional wave in the i i i , m/s Geoscience · Geophysical exploration methods interval velocity of the i i i , m/s Geoscience · Seismic acquisition and processing volume fraction of the i i i , fraction Logs and petrophysics · Overview of logging tools volume fraction of this mineral in the rock, fraction Logs and petrophysics · Gamma ray log and natural gamma ray spectrometry volume fraction of the i i i , fraction Logs and petrophysics · Porosity from the density log volume fraction of the i i i , fraction Logs and petrophysics · Lithology from the photoelectric factor and spectral gamma ray pore volume drained by the i i i , m³ Well testing · Pseudo-steady-state flow and the shape factor volume of the cell (rock together with pores), A Δ x i A\,\Delta x_i A Δ x i , m³ Simulation · Pressure equation for single-phase flow rock volume of the i i i , m³ Simulation · Permeability upscaling for single-phase flow V j V_j V j V k V_k V k V m V_m V m V p V_p V p P-wave speed, m/s Geoscience · Seismic waves, acoustic impedance and reflections pore volume of the compartment, m³ Geoscience · Reservoir architecture and performance volume of the voids that the given kind of porosity counts, cm³, m³ Reservoir engineering · Porosity pore volume (as a rule the open, that is connected, pores), m³, cm³ Reservoir engineering · Fluid saturation pore volume of the sample measured after extraction, cm³ Reservoir engineering · Fluid saturation pore volume, m³ Reservoir engineering · Rock compressibility and the effect of stress on core properties pore volume at the beginning of the interval, cm³ Reservoir engineering · Rock compressibility and the effect of stress on core properties pore volume of the drainage area, m³ Reservoir engineering · Flow regimes current pore volume of the accumulation, m³ Reservoir engineering · Performance prediction for solution gas drive reservoirs pore volume of the aquifer; d V p = 2 π f h ϕ r d r \dd V_p = 2\pi f h\phi\,r\dd r d V p = 2 π f h ϕ r d r , m³ Reservoir engineering · Unsteady-state water influx: the van Everdingen–Hurst method pore volume of the accumulation, m³ Reservoir engineering · Why water is injected: pressure maintenance and oil displacement pore volume of the element, ϕ A L \phi A L ϕ A L , m³ Reservoir engineering · Buckley–Leverett theory and the Welge method pore volume of the flooded formation or area, m³ Reservoir engineering · Displacement in heterogeneous reservoirs pore volume of the drainage area, m³ Well testing · Well testing: purposes and types of test pore volume of the area, π r e 2 h ϕ \pi r_e^2 h\phi π r e 2 h ϕ , m³ Well testing · Well testing: purposes and types of test pore volume of the closed area, m³ Well testing · Diagnosis with the pressure derivative pore volume of the area connected to the well, m³ Well testing · Build-up in a bounded reservoir and average reservoir pressure pore volume of the “tank”, m³ Simulation · What a reservoir simulation model is and why it is needed pore volume of the cell: its volume multiplied by the porosity, m³ Simulation · Types of reservoir simulation model pore volume of the cell, m³ Simulation · Types of reservoir simulation model pore volume of the cell at the reference pressure, m³ Simulation · Building a simulation model: input data and results V p , V s V_p,\ V_s V p , V s v s v_s v s v t v_t v t V t V_t V t V w V_w V w V R R \mathrm{VRR} VRR w w w initial water depth in the basin, km Geoscience · Structure and composition of the Earth steady settling velocity of the particle, m/s Geoscience · Sediment texture: grain size, sorting and shape channel width at bankfull level, m Geoscience · Continental environments: aeolian and fluvial horizontal distance between neighbouring contours, measured perpendicular to them, m Geoscience · Stress, strain and structural analysis heave (horizontal offset), at right angles to the strike, m Geoscience · Faults heave (horizontal amplitude) of the fault at this place, m Geoscience · Cross-sections from maps, map combination and faults on maps filter length: k k k Δ z \Delta z Δ z , m Logs and petrophysics · Log acquisition, processing and presentation weight of a metre of drill pipe in mud, kN/m Drilling · Drilling rig: power and hoisting systems weight of a metre of pipe in mud, N/m Drilling · Drill string design weight of a metre of drill collar in mud, N/m Drilling · Drill string design effective weight of a metre of pipe, N/m Drilling · Drill string design effective weight of a metre of string: the contribution of one metre to what the weight indicator shows, N/m Drilling · Wellheads and running casing mass fraction of calcium chloride in the water phase (water-phase salinity), fraction Drilling · Oil-based muds weight of a metre of collars in the mud, N/m Drilling · Deflection tools and downhole motors weight per metre of tubing in the fluid: steel plus the fluid inside minus the fluid displaced outside, N/m Production · Completion string equipment width of the propped fracture, m Production · Hydraulic fracturing: purpose and well selection rate of fresh wash water as a fraction of the oil volume, fraction Production · Oil treating: separators, dehydration, desalting and stabilisation specific work of compression, per kilogram of gas, J/kg Production · Gas processing and compression share of the project given to the partner, fraction Economics · Expected monetary value and preference theory the working interest that the partner gets, fraction Economics · Risk reduction and diversification W W W width of the coastal sand sheet across the shore, m Geoscience · Coastal, shallow-marine and deep-marine environments present horizontal distance between the pin and loose lines, m Geoscience · Practical structural geology width of the body (channel, channel belt, sand layer) across its axis, m Geoscience · Well correlation USBM index, — Reservoir engineering · Wettability and interfacial phenomena pore volume of the aquifer, which is also the initial volume of water in it (often written W i W_i W i , m³ Reservoir engineering · Aquifer models: water influx pore volume of the aquifer, m³ Reservoir engineering · Aquifer models: water influx channel width: the distance between the walls, W = L 1 + L 2 W = L_1 + L_2 W = L 1 + L 2 , m Well testing · Several boundaries: parallel faults and wedge-shaped blocks number of multiply–add operations, — Simulation · Solving systems of linear equations in simulators load on the lines: the weight of the string on the hook plus the weight of the travelling equipment, kN Drilling · Drilling rig: power and hoisting systems weight on bit, pound-force (lbf) Drilling · Abnormal formation pressures: origin, prediction and recognition hook load of the string (without the travelling block and the drive), N Drilling · Wellheads and running casing elastic energy stored in the twisted string, J Production · Progressing cavity pumps and hybrid systems accumulated volume injected by the end of the last period, m³ Production · Sources of formation damage water content: the mass of water in one cubic metre of gas at 20 °C and 0.101325 MPa, g/m³ Production · Gas processing and compression concentration of the inhibitor in the water phase (water plus inhibitor). The letter is the one used in the Hammerschmidt formula; it is not the water content of the gas W W W , % by mass Production · Gas processing and compression W e W_e W e w i w_i w i W i D W_{iD} W i D w ( t ) w(t) w ( t ) WC \text{WC} WC x x x distance from the ridge axis to the boundary of the magnetisation stripes, km Geoscience · Plate tectonics and sedimentary basins share of fine grains in the volume of the solid part (the grains, without the pores), fraction Geoscience · Sediment texture: grain size, sorting and shape horizontal distance along the direction of flow, m Geoscience · Traps and timing horizontal distance from the point above the centre, m Geoscience · Geophysical exploration methods offset between source and receiver, m Geoscience · Seismic acquisition and processing distance along the line from the point above the scatterer, m Geoscience · Seismic acquisition and processing value of the quantity, units of the quantity Geoscience · Distributions and sample size value of the parameter in this trial, units of the parameter Geoscience · Probabilistic volumetrics by Monte Carlo simulation value of the parameter, units of the parameter Geoscience · Probabilistic volumetrics by Monte Carlo simulation value of the parameter that corresponds to the random number u u u , units of the parameter Geoscience · Probabilistic volumetrics by Monte Carlo simulation distance from the left edge as a fraction of the grid width, — Logs and petrophysics · Log acquisition, processing and presentation number of hydrogen atoms per carbon atom in the average formula C H x \mathrm{CH}_x CH x , — Logs and petrophysics · Neutron log number of hydrogen atoms per carbon atom in the average formula C H x \mathrm{CH}_x CH x , — Logs and petrophysics · Gas, shale, carbonate and pressure effects on porosity logs number of hydrogen atoms per carbon atom, — Logs and petrophysics · Gas, shale, carbonate and pressure effects on porosity logs dimensionless variable on which the solution depends, — Reservoir engineering · Line-source solution and the pressure function argument, x > 0 x > 0 x > 0 , — Reservoir engineering · Line-source solution and the pressure function coordinate along the flow, from the injection side to the production side, m Reservoir engineering · Fractional flow function and mobility ratio coordinate along the flow, m Well testing · Inflow at high rates: non-Darcy flow the ratio τ 0 / τ w \tau_0/\tau_w τ 0 / τ w , — Drilling · Circulating pressure losses offset of the rig from the point above the wellhead, m Drilling · Offshore and subsea drilling distance along the wellbore from the toe to the heel, m Production · Horizontal wells amount of barium sulfate that comes out of a litre of the mixture, mol/L Production · Sources of formation damage volume fraction of the mineral that dissolves, in the solid part of the rock, fraction Production · Acid systems and treatment design X X X parameter of the curve C D e 2 S C_De^{2S} C D e 2 S , — Well testing · Type-curve matching the logarithmic term of an ideal well in pseudo-steady-state flow, — Production · Effect of completion on inflow logarithmic term of an ideal well in pseudo-steady-state flow (the pressure falls at the same pace everywhere in the drainage area), — Production · Acid treatments: principle, economics and candidate selection volume of mineral that a unit volume of acid solution dissolves (do not confuse it with the logarithmic term X = ln ( r e / r w ) − 3 / 4 X = \ln(r_e/r_w) - 3/4 X = ln ( r e / r w ) − 3/4 Acid treatments: principle, economics and candidate selection ), m³/m³ Production · Acid systems and treatment design volume dissolving power of the fluid for this mineral, m³/m³ Production · Acid systems and treatment design volume dissolving power of the acid (lesson on acid systems ), m³/m³ Production · Acid treatment of carbonates and special wells logarithmic term of an ideal well in pseudo-steady-state flow, — Production · Hydraulic fracturing: purpose and well selection an uncertain parameter: the reserves, a flow rate, the costs, units of the parameter Economics · Geological and technical uncertainty of a project the quantity being assessed: the reserves, million m³ Economics · Geological and technical uncertainty of a project x 0 x_0 x 0 x c x_c x c x i x_i x i the i i i , units of the quantity Geoscience · Descriptive statistics in geology reference curve (GR of the reference run) at the depths z i z_i z i , API Logs and petrophysics · Log acquisition, processing and presentation mole fraction of component i i i , — Reservoir engineering · Phase behaviour: pure substances and binary mixtures mole fraction of the component in the last drop of liquid, — Reservoir engineering · Phase behaviour: pure substances and binary mixtures mole fraction of the component in the phase: x i x_i x i y i y_i y i z i z_i z i , fraction Reservoir engineering · Cubic equations of state mole fraction of the component in the phase (in the gas it is denoted y i y_i y i , fraction Reservoir engineering · Cubic equations of state mole fraction of the component in the phase, fraction Reservoir engineering · Cubic equations of state margin: zero for a cased interval, and for the open hole taken from the caliper log and the experience of the area, fraction Drilling · Primary cementing x i , y i x_i,\ y_i x i , y i x s x_s x s x w x_w x w y y y distance from the neutral surface of the layer, which keeps its length: positive towards the convex side (the outer arc), negative towards the centre of curvature, m Geoscience · Folds, salt diapirs and their relationship to faults height of the horizon above the base of the syn-rift sequence in the hanging wall next to the fault, m Geoscience · Structural styles and tectonic history taper angle of the slips, 9°27′45″, degrees Drilling · Drill string design drop of the level in the annulus; the level in the string rises to the same depth, m Drilling · Wellheads and running casing mole fraction (for an ideal gas, also the volume fraction) of the component, fraction Production · Gas processing and compression Y Y Y y i y_i y i mole fraction of the component in the gas, fraction Reservoir engineering · Composition of reservoir fluids mole fraction of the component in the first gas bubbles, — Reservoir engineering · Phase behaviour: pure substances and binary mixtures mole fraction of the component in the gas; at the dew point, in the mixture, — Reservoir engineering · Phase behaviour: pure substances and binary mixtures mole fraction of component i i i , fraction Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) composition of the trial phase, fraction Reservoir engineering · Vapour–liquid equilibrium mole fraction of the component in the gas, fraction Production · Gas processing and compression mole fraction of the component in the gas (100 ppm = 10 − 4 10^{-4} 1 0 − 4 , — Production · Produced water: composition, treatment and disposal z z z depth, m Geoscience · Structure and composition of the Earth depth below the still-water level, m Geoscience · Primary sedimentary structures depth of burial, km Geoscience · Diagenesis: compaction, cementation and dissolution depth of water over the top of the buildup, m Geoscience · Carbonate sediments, environments and carbonate porosity regional depth of the horizon, m Geoscience · Practical structural geology depth of the centre of the sphere below the line of observation, m Geoscience · Geophysical exploration methods depth of the centre of the sphere, m Geoscience · Geophysical exploration methods depth of the top of the body, m Geoscience · Geophysical exploration methods depth of the reflecting boundary, m Geoscience · Geophysical exploration methods true depth of the reflection point, m Geoscience · Seismic acquisition and processing depth of the horizon below the datum, m Geoscience · Seismic interpretation depth below the top of the unit (below the datum), m Geoscience · Seismic interpretation distance from the mean in standard deviations, — Geoscience · Distributions and sample size depth of the reading on the run being matched, m Logs and petrophysics · Log acquisition, processing and presentation vertical depth from the surface (for deviated wells, measured vertically, not along the hole), m Logs and petrophysics · Formation water and formation temperature share of formation water in the water of the flushed zone, fraction Logs and petrophysics · Resistivity ratio methods and movable oil true vertical depth from the level where the water column begins (on land roughly from the ground surface, offshore from sea level), m Reservoir engineering · Reservoir pressure and temperature true vertical depth, m Reservoir engineering · Reservoir pressure and temperature burial depth, km Reservoir engineering · Porosity number of standard errors; about 2 for 95%, — Well testing · Comparing formation-tester, core and well-test data true vertical depth, measured downwards, m Well testing · Pressure gradients, fluid contacts and capillary equilibrium true vertical depth, measured downward, m Well testing · Pressure measurements in producing reservoirs: barriers and accuracy height above the base of the reservoir, m Simulation · Two-phase upscaling: pseudo-functions friction angle between the slips and the bushing (the bowl that holds the slips), arctan μ \arctan\mu arctan μ μ = 0.08 \mu = 0.08 μ = 0.08 K ≈ 4.0 K \approx 4.0 K ≈ 4.0 , degrees Drilling · Drill string design number of cutters passing over one circular track of the bottom, — Drilling · Drill bits: types and design true vertical depth, m Drilling · Bit selection and dull grading true vertical depth from the surface, m Drilling · Pore pressure and overburden pressure depth of the estimate (true vertical), m Drilling · Abnormal formation pressures: origin, prediction and recognition true vertical depth from the wellhead, m Drilling · Well control: primary barrier and kick indicators charge number of the counter-ion (for clays, the cation), — Drilling · Water-based muds and clay chemistry depth along the hole (along the tubing), measured from the wellhead downwards, m Production · Multiphase flow in tubing Z Z Z acoustic impedance of the rock, kg/(m²·s) Geoscience · Seismic waves, acoustic impedance and reflections gas deviation factor at the reservoir p p p T T T , — Geoscience · Volumetric estimation of hydrocarbons in place atomic number of the element, — Logs and petrophysics · Density log and photoelectric factor (Pe) gas deviation factor at pressure p p p T T T , — Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) gas deviation factor at p p p T T T , — Reservoir engineering · Gas formation volume factor, compressibility and viscosity Z-factor of the phase, Z = p V m / ( R T ) Z = pV_m/(RT) Z = p V m / ( R T ) , — Reservoir engineering · Cubic equations of state the root chosen for this phase: the smallest for the liquid, the largest for the gas, — Reservoir engineering · Cubic equations of state dimensionless cone height: the ratio of the “gravity” scale of the rate to the actual rate, — Well testing · Water and gas coning dimensionless cone height, — Well testing · Water and gas coning gas deviation factor (how far the real gas is from an ideal gas), averaged over the column, — Drilling · Pore pressure and overburden pressure gas deviation factor at p p p T T T , — Production · Oil treating: separators, dehydration, desalting and stabilisation gas deviation factor at suction (the correction for the difference between real and ideal gas), — Production · Gas processing and compression z 1 , z 2 z_1,\ z_2 z 1 , z 2 z i z_i z i height of the middle of the layer above the base of the body, m Geoscience · Facies, facies successions and sedimentary logs value at the i i i , m Geoscience · Structure maps and contouring mole fraction of component i i i , fraction Reservoir engineering · Composition of reservoir fluids mole fraction of component i i i , — Reservoir engineering · Types of reservoir fluids mole fraction of the component in the original mixture, fraction Reservoir engineering · Vapour–liquid equilibrium composition of the mixture, fraction Reservoir engineering · Vapour–liquid equilibrium composition of the original mixture, — Reservoir engineering · Vapour–liquid equilibrium depths of the points of the line, m Well testing · Pressure gradients, fluid contacts and capillary equilibrium z ref z_{\text{ref}} z ref α \alpha α flexural parameter — the characteristic length of bending, m Geoscience · Plate tectonics and sedimentary basins angle between the strike of the structure and the strike of the strike-slip fault; for a right-lateral fault it is measured clockwise, for a left-lateral one anticlockwise, ° Geoscience · Structural styles and tectonic history angle between the axis of the body and the line joining the wells, ° Geoscience · Well correlation regularisation parameter, — Logs and petrophysics · Nuclear magnetic resonance (NMR) logging the “water” term: the conductivity of the rock at S w = 1 S_w = 1 S w = 1 α = ϕ m / ( a R w ) \alpha = \phi^m/(a R_w) α = ϕ m / ( a R w ) , S/m Logs and petrophysics · Water saturation in shaly sands angle of the axis x x x , rad Reservoir engineering · Relative permeability angle of the axis x x x , rad Reservoir engineering · Fractional flow function and mobility ratio dip angle of the formation (in absolute value: one formula serves for water going up the dip and for gas going down the dip), rad Reservoir engineering · Segregated flow and gravity displacement dip angle of the formation. For drainage in the vertical direction sin α = 1 \sin\alpha = 1 sin α = 1 k k k A A A , rad Reservoir engineering · Segregated flow and gravity displacement angle of the flow axis to the horizontal: positive if the gas moves up the dip, rad Reservoir engineering · Displacement of oil by gas 0.5 for M ′ ≤ 1 M' \le 1 M ′ ≤ 1 1 < M ′ ≤ 10 1 < M' \le 10 1 < M ′ ≤ 10 0.14 ≤ M ′ ≤ 7.3 0.14 \le M' \le 7.3 0.14 ≤ M ′ ≤ 7.3 , — Well testing · Water and gas coning allowed relative deviation of the pressure from the unit-slope line: 0.01, 0.05 or 0.10, — Well testing · Wellbore storage dimensionless fault transmissibility, — Well testing · Partially communicating faults ratio of the radii of neighbouring boundaries, — Simulation · Grids in reservoir simulation models phase: o o o w w w , — Simulation · Two-phase flow equations Biot coefficient, from 0 to 1; close to 1 for loose and moderately compacted rocks, — Drilling · Pore pressure and overburden pressure attenuation of the casing wave over the stretch between the two receivers, dB/m Drilling · Remedial cementing, cement plugs and cement evaluation sharpness of the separation: the larger it is, the steeper the curve, — Drilling · Solids control in drilling fluids attenuation coefficient, 1/m Drilling · Measurement while drilling the fraction of the clay strength that is used at the wall: small right after jetting, growing with time, — Drilling · Offshore and subsea drilling coefficient of linear thermal expansion of steel (how much each unit of length grows per degree), 1.24 ⋅ 10 − 5 1.24\cdot10^{-5} 1.24 ⋅ 1 0 − 5 , 1/°C Production · Completion string equipment coefficient of linear expansion of steel, 1.24 ⋅ 10 − 5 1.24\cdot 10^{-5} 1.24 ⋅ 1 0 − 5 , 1/°C Production · Wireline operations thermal diffusivity of the rocks, m²/s Production · Chokes, surface pressure losses and well temperature volume fraction of gas in the mixture, — Production · Chokes, surface pressure losses and well temperature temperature coefficient of the resistance of copper, 0.0039, 1/°C Production · Electric submersible pumps (ESP) Biot coefficient, from 0 to 1, — Production · Rock mechanics for hydraulic fracturing β \beta β stretching factor: the factor by which the crust and lithosphere have thinned, — Geoscience · Plate tectonics and sedimentary basins dip angle of the beds — the angle of rotation, ° Geoscience · Primary sedimentary structures compaction coefficient, MPa⁻¹ Geoscience · Diagenesis: compaction, cementation and dissolution angle between the line of the section and the strike, ° Geoscience · Stress, strain and structural analysis stretching factor: how many times a section across the strike of the faults has lengthened, — Geoscience · Structural styles and tectonic history dip of its image on the unmigrated section when the section is redrawn in depth by V t 0 / 2 V t_0/2 V t 0 /2 , ° Geoscience · Seismic acquisition and processing volumetric thermal expansion coefficient of the oil, 1/°C Reservoir engineering · Systems of units: SI, oilfield and metric oilfield thermal expansion coefficient of the stock-tank oil near these temperatures (the fraction by which the volume grows per degree); around 20 °C it is roughly ( 0.6 – 1.0 ) ⋅ 10 − 3 (0.6\text{–}1.0)\cdot 10^{-3} ( 0.6 – 1.0 ) ⋅ 1 0 − 3 , 1/°C Reservoir engineering · Density and compressibility of reservoir oil inertial resistance coefficient of the rock, m⁻¹ Reservoir engineering · Rock permeability angle between the interface and the bedding, rad Reservoir engineering · Segregated flow and gravity displacement inertial resistance coefficient of the rock, m⁻¹ Well testing · Inflow at high rates: non-Darcy flow inertial resistance coefficient, m⁻¹ Well testing · Inflow at high rates: non-Darcy flow tilt angle of the contact; in practice tan β \tan\beta tan β , m/km Well testing · Perched and tilted contacts, trapped water journal angle to the horizontal — also the angle between the cone axis and the generator lying on the bottom, degrees Drilling · Drill bits: types and design angle between the vertical and the line that joins the target with the centre of the arc; it is negative if the departure is smaller than the radius, degrees Drilling · Directional wells: applications and profile dogleg over the sliding interval, degrees Drilling · Deflection tools and downhole motors dogleg over the interval, degrees Drilling · Deflection tools and downhole motors the angle between the directions of the well at the upper and the lower points of the interval, degrees Drilling · Directional survey calculations dogleg, degrees or radians Drilling · Directional survey calculations inertial resistance coefficient of the gravel, m⁻¹ Production · Effect of completion on inflow the common marginal return of gas: how much oil one more thousand cubic metres of gas would give, m³ of oil per thousand m³ Production · Gas lift: principles and choice of operating conditions inertial resistance coefficient of the rock, m⁻¹ Production · Formation damage and damage skin mass of mineral that a unit mass of pure acid dissolves, kg/kg Production · Acid systems and treatment design beta coefficient: how strongly the return on the shares of the company follows the market (β = 1 \beta = 1 β = 1 β > 1 \beta > 1 β > 1 , — Economics · Choosing the discount rate γ \gamma γ shear strain, — Geoscience · Stress, strain and structural analysis angle between the axis of the hole and the normal to the bedding, ° Geoscience · Stress, strain and structural analysis angle between the well and the normal to the fractures of the set, ° Geoscience · Fractures and naturally fractured reservoirs angle between the hole and the normal to the bedding: cos γ = ∣ sin δ sin θ cos ( a − φ ) − cos δ cos θ ∣ \cos\gamma = |\sin\delta\,\sin\theta\,\cos(a - \varphi) - \cos\delta\,\cos\theta| cos γ = ∣ sin δ sin θ cos ( a − φ ) − cos δ cos θ ∣ , ° Geoscience · Well correlation gyromagnetic ratio of the proton (a constant of the proton), 2.675 ⋅ 10 8 2.675\cdot10^{8} 2.675 ⋅ 1 0 8 γ / 2 π = 42.58 \gamma/2\pi = 42.58 γ /2 π = 42.58 , rad/(s·T) Logs and petrophysics · Nuclear magnetic resonance (NMR) logging gyromagnetic ratio of the proton, rad/(s·T) Logs and petrophysics · Nuclear magnetic resonance (NMR) logging coefficient of the shale term; it depends on the amount of shale and its conductivity, S/m Logs and petrophysics · Water saturation in shaly sands specific gravity of the fraction relative to water at 60 °F, — Reservoir engineering · Composition of reservoir fluids coefficient of the sensitivity of permeability to pressure (permeability modulus), 1/MPa Reservoir engineering · Rock compressibility and the effect of stress on core properties e 0.5772 = 1.781 \e^{0.5772} = 1.781 e 0.5772 = 1.781 , — Well testing · Pseudo-steady-state flow and the shape factor e 0.5772 = 1.781 \e^{0.5772} = 1.781 e 0.5772 = 1.781 , — Well testing · Dimensionless well solutions: skin, radius of investigation and units the exponential of Euler's constant, 1.781, — Well testing · Pressure build-up analysis the exponential of Euler's constant, — Well testing · A sealing fault near the well: the method of images 1.781, the exponential of Euler's constant, — Well testing · Reservoir limit test adiabatic index; for nitrogen at moderate pressures about 1.4, — Drilling · Blowout prevention equipment angle between this line and the tangent section; under the root is the square of the distance from the centre of the arc to the target, degrees Drilling · Directional wells: applications and profile grid convergence , the angle from true north to grid north; plus if grid north is east of true north, degrees Drilling · Directional survey calculations grid convergence: the angle from true north to grid north, positive if grid north lies to the east, degrees Drilling · Survey instruments: magnetic, gyroscopic and inertial e 0.5772 = 1.781 \e^{0.5772} = 1.781 e 0.5772 = 1.781 1 / ( 2 γ ) = 0.2807 1/(2\gamma) = 0.2807 1/ ( 2 γ ) = 0.2807 , — Production · Inflow to a hydraulically fractured well γ ˙ \dot\gamma γ ˙ δ \delta δ desired half-width of the ± 2 S E \pm 2\,SE ± 2 S E , fraction Geoscience · Sedimentary rocks and their classification dip angle of the plane, ° Geoscience · Primary sedimentary structures dip angle of the laminae, ° Geoscience · Continental environments: aeolian and fluvial true dip, ° Geoscience · Stress, strain and structural analysis dip of the bed, ° Geoscience · Stress, strain and structural analysis dip angle, ° Geoscience · Stress, strain and structural analysis dip of the fault plane, ° Geoscience · Faults present dip of the faults, ° Geoscience · Structural styles and tectonic history dip angle of the fault plane, ° Geoscience · Cross-sections from maps, map combination and faults on maps skin depth: the distance over which the amplitude of the alternating field falls by a factor of e ≈ 2.72 e \approx 2.72 e ≈ 2.72 , m Logs and petrophysics · Resistivity logs: electrical and induction tools margin for the inaccuracy of the saturation pressure, MPa Reservoir engineering · Reservoir fluid sampling distance from the axis of the well to the nearest boundary, m Well testing · Semi-infinite systems: theory and test analysis constant error of the gauge in this survey, Pa Well testing · Forced-gradient technique and multi-well analysis penetration of the bit per revolution, mm/rev Drilling · Drill bits: types and design bend angle (the angle of the tilt) between the axis of the lower part of the assembly and the axis of the motor, degrees Drilling · Deflection tools and downhole motors magnetic declination , the angle from true north to magnetic north; east is plus, west is minus, degrees Drilling · Directional survey calculations deviation of the indicator; a minus sign means less than the project value, % Economics · State regulation of field development Δ \Delta Δ Δ ρ \Delta\rho Δ ρ density contrast between the body and the host rocks; for salt among compacted sediments it is negative, kg/m³ Geoscience · Geophysical exploration methods difference between the densities of water and oil, ρ w − ρ o \rho_w - \rho_o ρ w − ρ o , kg/m³ Reservoir engineering · Fractional flow function and mobility ratio density difference between the displacing phase and the oil, kg/m³ Reservoir engineering · Segregated flow and gravity displacement density difference between water and oil at reservoir conditions, kg/m³ Reservoir engineering · Displacement in heterogeneous reservoirs density difference of the phases, kg/m³ Simulation · Petrophysical input for simulation: relative permeability and capillary pressure difference between the densities of the grain and of the fluid, kg/m³ Production · Fracturing fluids and tip-screenout fracturing absolute value of the difference between the densities of the droplet and of the continuous phase, kg/m³ Production · Oil treating: separators, dehydration, desalting and stabilisation ε \varepsilon ε relative shortening, — Geoscience · Practical structural geology correction term (formula below), K Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) correction term, °R Reservoir engineering · Ideal and real gas: the gas deviation factor (Z) how many times the error must be reduced (the equation uses the reciprocal of that number), — Simulation · Solving systems of linear equations in simulators tolerance: the relative residual at which the iterations are stopped, — Simulation · Solving systems of linear equations in simulators absolute roughness of the wall, m Drilling · Circulating pressure losses zero offset of each of the two rate sensors, °/h Drilling · Survey instruments: magnetic, gyroscopic and inertial absolute roughness of the wall, m Production · Multiphase flow in tubing exponent of the law of growth of the concentration; it is also the pad fraction of the pumped volume, — Production · Fracture design: size and conductivity price elasticity: of demand (ε d \varepsilon_d ε d ε s \varepsilon_s ε s , — Economics · The oil industry in history: demand, supply and prices ε 0 \varepsilon_0 ε 0 ζ \zeta ζ η \eta η fraction of filtrate in the inflowing fluid by volume at reservoir conditions, fraction Reservoir engineering · Reservoir fluid sampling fraction of filtrate in the reservoir volume, fraction Reservoir engineering · Reservoir fluid sampling hydraulic diffusivity , m²/s Reservoir engineering · Flow regimes hydraulic diffusivity ; in Russian-language literature it is also written κ \kappa κ χ \chi χ , m²/s Reservoir engineering · Diffusivity equation hydraulic diffusivity k / ( ϕ μ c t ) k/(\phi\mu c_t) k / ( ϕ μ c t ) , m²/s Reservoir engineering · Line-source solution and the pressure function hydraulic diffusivity of the aquifer, k / ( ϕ μ w c t ) k/(\phi\mu_wc_t) k / ( ϕ μ w c t ) , m²/s Reservoir engineering · Aquifer models: water influx hydraulic diffusivity k / ( ϕ μ c t ) k/(\phi\mu c_t) k / ( ϕ μ c t ) , m²/s Well testing · Dimensionless well solutions: skin, radius of investigation and units hydraulic diffusivity (how fast a pressure change spreads through the rock), m²/s Well testing · Several boundaries: parallel faults and wedge-shaped blocks hydraulic diffusivity, m²/s Well testing · Several boundaries: parallel faults and wedge-shaped blocks hydraulic diffusivity k / ( ϕ μ c t ) k/(\phi\mu c_t) k / ( ϕ μ c t ) , m²/s Well testing · Semi-infinite systems: theory and test analysis hydraulic diffusivity, 0.0853 k / ( ϕ μ c t ) 0.0853\,k/(\phi\mu c_t) 0.0853 k / ( ϕ μ c t ) , m²/d Simulation · Finite differences: from equations to computation block efficiency — the ratio of the load to the ideal force n F fl nF_{\text{fl}} n F fl , — Drilling · Drilling rig: power and hoisting systems dynamic viscosity of the fluid, Pa·s Drilling · Drilling fluid rheology and flow regimes share of the force of the tensioners that reaches the riser along the vertical (friction, tilt of the wire ropes), — Drilling · Offshore and subsea drilling system efficiency: the share of the energy supplied that goes into lifting the liquid, — Production · Artificial lift: when it is needed and how to choose the method efficiency of the stage, which is also the efficiency of a pump made of identical stages, — Production · Electric submersible pumps (ESP) fluid efficiency : the share of the pumped volume that is in the fracture at the end of injection, — Production · Fracture design: size and conductivity fluid efficiency at the end of injection, — Production · Fracture design: size and conductivity efficiency of the power plant: the share of the heat of combustion that becomes electricity, — Production · Field development concepts: surface facilities adiabatic (isentropic) efficiency of the stage: the ideal work divided by the real work, — Production · Gas processing and compression η v \eta_v η v θ \theta θ Shields number, — Geoscience · Primary sedimentary structures contact angle (the angle at which the boundary between the fluids meets the rock surface), measured through the water; close to zero for a water-wet rock (one whose surface prefers water), ° Geoscience · Reservoir and seal angle between the direction of σ 1 \sigma_1 σ 1 , ° Geoscience · Stress, strain and structural analysis angle between the strike of the fracture and the direction of σ H \sigma_H σ H , ° Geoscience · Practical structural geology angle of incidence of the P-wave on the boundary, ° Geoscience · Seismic waves, acoustic impedance and reflections true dip of the boundary, the dip angle of the layer (in the lessons on structural geology it is δ \delta δ θ \theta θ on AVO , ° Geoscience · Seismic acquisition and processing largest dip that must be imaged, ° Geoscience · Seismic acquisition and processing contact angle, measured through the water, degrees Reservoir engineering · Wettability and interfacial phenomena contact angle, measured through the wetting phase, degrees Reservoir engineering · Capillary pressure and the transition zone angle between the wellbore and the normal to the reservoir, degrees Well testing · Partial penetration and well deviation angle between the faults on the side of the well, degrees Well testing · Several boundaries: parallel faults and wedge-shaped blocks angle of the sector; a full circle is 2 π 2\pi 2 π , rad Simulation · Interblock flow and transmissibility angle between the first principal axis and the x x x , ° Simulation · Interblock flow and transmissibility inclination of the hole in the interval of the assembly, degrees Drilling · Drill string design inclination, degrees Drilling · Drill string design inclination of the section, degrees Drilling · Drill string design reading of the instrument, degrees on the dial Drilling · Drilling fluid rheology and flow regimes inclination of the tangent section, degrees Drilling · Directional wells: applications and profile inclination of the tangent section; in the first formula in degrees, degrees Drilling · Directional wells: applications and profile inclination at the end of the build and in the tangent section, degrees or radians Drilling · Directional wells: applications and profile inclination of the hole — the deviation from the vertical; cos θ d z \cos\theta\,\dd z cos θ d z , — Production · Multiphase flow in tubing angle of twist of the string, rad Production · Progressing cavity pumps and hybrid systems angle on the wall, measured from the direction of σ H \sigma_H σ H , rad Production · Rock mechanics for hydraulic fracturing angle from the direction of σ H \sigma_H σ H , rad Production · Rock mechanics for hydraulic fracturing central angle of the segment, rad Production · Oil treating: separators, dehydration, desalting and stabilisation θ ˉ \bar\theta θ ˉ θ , φ \theta,\ \varphi θ , φ θ i \theta_i θ i κ \kappa κ thermal diffusivity of rocks; typically 0.8 ⋅ 10 − 6 0.8\cdot10^{-6} 0.8 ⋅ 1 0 − 6 , m²/s Geoscience · Plate tectonics and sedimentary basins magnetic susceptibility of the body relative to the host rocks, SI units (dimensionless) Geoscience · Geophysical exploration methods condition number λ max ( A ) / λ min ( A ) \lambda_{\max}(\mathbf{A})/\lambda_{\min}(\mathbf{A}) λ m a x ( A ) / λ m i n ( A ) , — Simulation · Solving systems of linear equations in simulators condition number of the matrix, — Simulation · Solving systems of linear equations in simulators condition number, — Simulation · Solving systems of linear equations in simulators curvature of the hole: the dogleg severity (how fast the hole bends along its length) converted to radians per metre, rad/m Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe curvature of the hole, rad/m Drilling · Drill string design overall rate constant of dissolving: it covers both the delivery of acid to the wall and the reaction on it; the slower of the two decides it, m/s Production · Acid treatment of carbonates and special wells a factor that takes into account that parts of the wall opened at different times: from 1.42 (PKN without leak-off) to π / 2 ≈ 1.57 \pi/2 \approx 1.57 π /2 ≈ 1.57 , — Production · Fracture design: size and conductivity λ \lambda λ thermal conductivity of the rocks of the layer, W/(m·K) Geoscience · Structure and composition of the Earth decay constant — the fraction of nuclei that decay per unit time, yr⁻¹ Geoscience · Stratigraphy and geologic time decay constant of ⁸⁷Rb, 1.3972 ⋅ 10 − 11 1.3972\cdot 10^{-11} 1.3972 ⋅ 1 0 − 11 , yr⁻¹ Geoscience · Stratigraphy and geologic time dune spacing — the distance between adjacent crests (or troughs), m Geoscience · Continental environments: aeolian and fluvial wavelength: the distance between neighbouring crests (compressions), m Geoscience · Seismic waves, acoustic impedance and reflections thermal conductivity of the rocks of the layer: shales 1–2, sandstones and carbonates 2–4, rock salt about 5–6 W/(m·K), W/(m·K) Reservoir engineering · Reservoir pressure and temperature pore-size distribution index: the larger it is, the more uniform the pores and the sharper the transition, — Reservoir engineering · Fluid saturation decay exponent, 1/s Well testing · Build-up in a bounded reservoir and average reservoir pressure non-zero eigenvalues of C − 1 K \mathbf C^{-1}\mathbf K C − 1 K , 1/d Well testing · Lumped multi-tank material balance model size of the heterogeneity in the given direction: the correlation length of permeability, m Simulation · Special topics in upscaling rate of decline: the fraction of the speed lost per hour, 1/h Drilling · Bit performance and cost per metre Darcy friction factor (Haaland formula, Multiphase flow in tubing ), — Production · Horizontal wells Darcy–Weisbach friction factor; in turbulent flow in steel pipes usually 0.015–0.03, — Production · Nodal analysis of the production system Darcy–Weisbach friction factor, — Production · Multiphase flow in tubing Darcy friction factor, — Production · Multiphase flow in tubing Darcy friction factor (from the Haaland formula), — Production · Water injection systems λ o , λ w \lambda_o,\ \lambda_w λ o , λ w λ t \lambda_t λ t μ \mu μ dynamic viscosity of water (its resistance to flow); about 1.00 ⋅ 10 − 3 1.00\cdot10^{-3} 1.00 ⋅ 1 0 − 3 , Pa·s Geoscience · Sediment texture: grain size, sorting and shape viscosity of the fluid, Pa·s Geoscience · Fractures and naturally fractured reservoirs viscosity of the fluid that flows through the baffle, Pa·s Geoscience · Reservoir architecture and performance mean; for the normal distribution it is also the median and the mode, units of the quantity Geoscience · Distributions and sample size mean of the natural logarithm of the quantity, — Geoscience · Distributions and sample size true mean of the population, units of the quantity Geoscience · Distributions and sample size Lagrange multiplier, a number that accounts for the condition that the weights add up to one, units² Geoscience · Spatial correlation and the variogram mean, units of the parameter Geoscience · Probabilistic volumetrics by Monte Carlo simulation dynamic viscosity, Pa·s Reservoir engineering · Oil viscosity and interfacial tension viscosity of the displacing phase (water), Pa·s Reservoir engineering · Oil viscosity and interfacial tension dynamic viscosity of the liquid, Pa·s Reservoir engineering · Laboratory PVT tests attenuation coefficient of the material; it grows with density and with the atomic number of the elements, 1/cm Reservoir engineering · Core analysis dynamic viscosity of the fluid, Pa·s Reservoir engineering · Rock permeability viscosity of the fluid at reservoir conditions, Pa·s Reservoir engineering · Rock permeability viscosity of the fluid, Pa·s Reservoir engineering · Flow regimes fluid viscosity at reservoir conditions, Pa·s Well testing · Steady-state radial flow dynamic viscosity of the fluid, Pa·s Well testing · Inflow at high rates: non-Darcy flow fluid viscosity, Pa·s Well testing · Well testing: purposes and types of test viscosity of the fluid in the reservoir, mPa·s Well testing · Pressure drawdown analysis viscosity of the fluid that flows in, usually the mud filtrate, Pa·s Well testing · Pressure measurement with the wireline formation tester viscosity of the fluid that flows across, Pa·s Well testing · Pressure measurements in producing reservoirs: barriers and accuracy fluid viscosity (the resistance of the fluid to flow), Pa·s Simulation · What a reservoir simulation model is and why it is needed dynamic viscosity of the oil, mPa·s Simulation · Types of reservoir simulation model fluid viscosity, Pa·s Simulation · Types of reservoir simulation model viscosity of the fluid, Pa·s Simulation · Pressure equation for single-phase flow viscosity, mPa·s Simulation · Permeability upscaling for single-phase flow friction factor. The plus sign is for pulling out and the minus sign for running in. When rotating, there is no term with μ \mu μ , — Drilling · Drill string design bit friction coefficient: it covers both cutting and friction; for PDC bits it is usually larger than for roller-cone bits, — Drilling · Bit performance and cost per metre viscosity of the liquid around the particle, Pa·s Drilling · Solids control in drilling fluids viscosity; for a mud, the effective viscosity μ eff \mu_{\text{eff}} μ eff , Pa·s Drilling · Drilling fluid rheology and flow regimes viscosity; for a mud, the plastic viscosity, Pa·s Drilling · Circulating pressure losses viscosity, Pa·s Drilling · Circulating pressure losses viscosity of the oil at reservoir conditions, Pa·s Production · Inflow performance relationship (IPR) dynamic viscosity of the liquid, Pa·s Production · Progressing cavity pumps and hybrid systems viscosity of the injected fluid in the reservoir (close to the viscosity of the reservoir fluid), Pa·s Production · Acid systems and treatment design coefficient of friction on the fault; for most rocks 0.6–1.0, — Production · Rock mechanics for hydraulic fracturing apparent viscosity of the fluid in the fracture, Pa·s Production · Fracture design: size and conductivity viscosity of a Newtonian fluid, Pa·s Production · Fracturing fluids and tip-screenout fracturing viscosity of the fluid, Pa·s Production · Sand production: types, prediction and cost of the problem μ , B \mu,\ B μ , B μ , k , h \mu,\ k,\ h μ , k , h fluid viscosity, permeability and reservoir thickness, Pa·s, m², m Reservoir engineering · Line-source solution and the pressure function viscosity, permeability, thickness of the reservoir, Pa·s, m², m Well testing · Wellbore storage in the dimensional forms: viscosity of the fluid, permeability and thickness of the reservoir, mPa·s or cP; mD; m or ft Well testing · Wellbore storage μ 0 \mu_0 μ 0 μ a \mu_a μ a μ f \mu_f μ f μ g , μ o \mu_g,\ \mu_o μ g , μ o μ o \mu_o μ o μ w \mu_w μ w μ w , μ o \mu_w,\ \mu_o μ w , μ o ν \nu ν Poisson's ratio; typically 0.25, — Geoscience · Plate tectonics and sedimentary basins kinematic viscosity of water; at 20 °C about 1.0 ⋅ 10 − 6 1.0\cdot10^{-6} 1.0 ⋅ 1 0 − 6 , m²/s Geoscience · Primary sedimentary structures dynamic Poisson's ratio (the ratio of the sideways shortening to the lengthening when the rock is stretched), — Logs and petrophysics · Sonic log kinematic viscosity , m²/s Reservoir engineering · Oil viscosity and interfacial tension Poisson's ratio of the rock (how much a rock bulges sideways when it is squeezed lengthwise), — Reservoir engineering · Rock compressibility and the effect of stress on core properties Poisson's ratio, — Reservoir engineering · Rock compressibility and the effect of stress on core properties iteration number; the initial approximation x ( 0 ) \mathbf{x}^{(0)} x ( 0 ) , — Simulation · IMPES and fully implicit schemes number of iterations needed to reduce the error by a factor of 1 / ε 1/\varepsilon 1/ ε , — Simulation · Solving systems of linear equations in simulators Poisson's ratio in the sense of the method: a parameter fitted to the tests in the area (the real Poisson's ratio shows how much a rock expands sideways when it is squeezed along its axis), — Drilling · Fracture gradient and leak-off testing number of ions in the formula of the salt: 3 for CaCl₂, 2 for NaCl, — Drilling · Oil-based muds Poisson's ratio of steel, 0.3, — Production · Completion string equipment static Poisson's ratio of the layer, — Production · Rock mechanics for hydraulic fracturing ξ \xi ξ Π \Pi Π ρ \rho ρ density, kg/m³ Geoscience · Structure and composition of the Earth density of the rock, kg/m³ Geoscience · Structure and composition of the Earth density of the fragment, g/cm³ Geoscience · Minerals and rocks plunge of the line, ° Geoscience · Stress, strain and structural analysis density of the intermediate layer — the rocks between the station and the reference level, g/cm³ Geoscience · Geophysical exploration methods bulk density of the rock, kg/m³ Geoscience · Seismic waves, acoustic impedance and reflections the specified correlation coefficient, from −1 to 1, — Geoscience · Probabilistic volumetrics by Monte Carlo simulation density of the solution; for NaCl solutions near 20 °C, approximately ρ ≈ 1 + 0.73 w \rho \approx 1 + 0.73\,w ρ ≈ 1 + 0.73 w w w w , g/cm³ (= kg/L) Logs and petrophysics · Formation water and formation temperature density of the oil at the temperature to which the barrel volume is referred (60 °F), t/m³ Reservoir engineering · Systems of units: SI, oilfield and metric oilfield fluid density at reservoir conditions, kg/m³ Reservoir engineering · Reservoir pressure and temperature density of the fluid that fills the reservoir between these depths, at reservoir conditions, kg/m³ Reservoir engineering · Reservoir pressure and temperature fluid density at the same conditions, kg/m³ Reservoir engineering · Oil viscosity and interfacial tension density of the fluid, kg/m³ Reservoir engineering · Rock permeability density of the fluid at reservoir conditions, kg/m³ Reservoir engineering · Diffusivity equation density of the liquid in the tubing, kg/m³ Well testing · Well inflow: the well performance diagram fluid density, kg/m³ Well testing · Inflow at high rates: non-Darcy flow density of the liquid in the wellbore, kg/m³ Well testing · Nonideal wellbore storage, well clean-up and changing skin density of the liquid, kg/m³ Well testing · Nonideal wellbore storage, well clean-up and changing skin fluid density at reservoir conditions, kg/m³ Well testing · Pressure measurements in producing reservoirs: barriers and accuracy fluid density, kg/m³ Drilling · Pore pressure and overburden pressure reading of the balance after topping up with water, g/cm³ Drilling · Abnormal formation pressures: origin, prediction and recognition density of the liquid passing through the choke, kg/m³ Drilling · Blowout prevention equipment density of the fluid, kg/m³ Drilling · Drilling fluid rheology and flow regimes density of the mud, kg/m³ Drilling · Bit hydraulics optimisation density of the mud (with gas, the average by volume), kg/m³ Drilling · Measurement while drilling density of the liquid in the tubing, kg/m³ Production · Nodal analysis of the production system density of the liquid, kg/m³ Production · Chokes, surface pressure losses and well temperature fluid density at reservoir conditions, kg/m³ Production · Effect of completion on inflow density of the liquid in the well, kg/m³ Production · Artificial lift: when it is needed and how to choose the method density of the liquid in the tubing and below the pump, kg/m³ Production · Artificial lift: when it is needed and how to choose the method density of the pumped liquid at the conditions in the pump, kg/m³ Production · Electric submersible pumps (ESP) density of the liquid in the tubing and in the annulus below the level, kg/m³ Production · Electric submersible pumps (ESP) density of the power fluid, kg/m³ Production · Hydraulic pumps: piston and jet density of the liquid (of the mixture, if it carries proppant), kg/m³ Production · Perforating operations: gun conveyance and procedures density of the fluid in the pipes, kg/m³ Production · Acid systems and treatment design density of the injected water, kg/m³ Production · Water injection systems correlation coefficient between X X X Y Y Y , — Economics · Geological and technical uncertainty of a project the correlation of the outcomes: “success” is taken as one, “failure” as zero, — Economics · Risk reduction and diversification ρ ˉ \bar\rho ρ ˉ ρ , g \rho,\ g ρ , g ρ 1 , ρ 2 \rho_1,\ \rho_2 ρ 1 , ρ 2 ρ b \rho_b ρ b bulk density of the rock, g/cm³ Logs and petrophysics · Gamma ray log and natural gamma ray spectrometry bulk density from the density log, kg/m³ Logs and petrophysics · Sonic log bulk density of the substance, g/cm³ Logs and petrophysics · Density log and photoelectric factor (Pe) bulk density of the rock from the log, g/cm³ Logs and petrophysics · Porosity from the density log bulk density of the formation from the log, the average over the laminae, g/cm³ Logs and petrophysics · Porosity from the density log bulk density from the log, corrected for environmental conditions, g/cm³ Logs and petrophysics · Lithology and porosity from crossplots bulk density from the log, g/cm³ Logs and petrophysics · M–N and MID plots for complex lithologies bulk density of the rock measured by the tool, g/cm³ Reservoir engineering · Porosity bulk density of the rock, g/cm³ Drilling · Pore pressure and overburden pressure density of the brine (the water phase), g/cm³ Drilling · Field testing of drilling fluids density of the brine; for CaCl₂ about 1.08 at 10%, 1.18 at 20%, 1.28 at 30%, g/cm³ Drilling · Oil-based muds ρ b ( z ) \rho_b(z) ρ b ( z ) ρ c \rho_c ρ c ρ f \rho_f ρ f density of water; about 998 at 20 °C, kg/m³ Geoscience · Sediment texture: grain size, sorting and shape average density of the fluid in the pores of the zone of investigation, g/cm³ Logs and petrophysics · Porosity from the density log fluid density: 1.0 g/cm³ for fresh filtrate, about 1.1 for salty filtrate, g/cm³ Logs and petrophysics · Lithology and porosity from crossplots fluid density in the flushed zone (fresh filtrate 1.00), g/cm³ Logs and petrophysics · Lithology from the photoelectric factor and spectral gamma ray fluid density: 1.00 for fresh filtrate, about 1.1 for salty filtrate, g/cm³ Logs and petrophysics · M–N and MID plots for complex lithologies density of the fluid in the zone of investigation (usually the filtrate), g/cm³ Logs and petrophysics · Resistivity–porosity crossplots density of the fluid in the zone the tool reads, usually mud filtrate (the liquid from the drilling mud that has seeped into the rock): about 1.0 for fresh mud, up to 1.1–1.2 for salty mud, g/cm³ Reservoir engineering · Porosity density of the pore fluid, g/cm³ Drilling · Pore pressure and overburden pressure ρ g \rho_g ρ g ρ i \rho_i ρ i ρ j \rho_j ρ j ρ kill \rho_{\text{kill}} ρ kill ρ m \rho_m ρ m density of the upper mantle, g/cm³ Geoscience · Structure and composition of the Earth density of the mantle beneath the plate, kg/m³ Geoscience · Plate tectonics and sedimentary basins drilling mud density, kg/m³ Drilling · Pore pressure and overburden pressure mud density (sometimes the equivalent circulating density is taken, which adds the effect of friction while the mud flows), g/cm³ Drilling · Abnormal formation pressures: origin, prediction and recognition density of the mud that fills the annulus now, kg/m³ Drilling · Fracture gradient and leak-off testing density of the mud without gas, g/cm³ Drilling · Well control: primary barrier and kick indicators density of the mud in the drill pipe, kg/m³ Drilling · Well kill methods density of the current mud, kg/m³ Drilling · Well kill methods mud density, kg/m³ Drilling · Wellheads and running casing density of the drilling mud, kg/m³ Drilling · Wellheads and running casing density of the mud in the well, g/cm³ Drilling · Casing design density of the mud (from the pressurised balance), g/cm³ Drilling · Field testing of drilling fluids ρ m a \rho_{ma} ρ ma density of the mineral matrix, g/cm³ Logs and petrophysics · Porosity from the density log matrix density assumed in the calculation of ϕ D \phi_D ϕ D , g/cm³ Logs and petrophysics · Gas, shale, carbonate and pressure effects on porosity logs matrix density, g/cm³ Logs and petrophysics · Resistivity–porosity crossplots grain (matrix) density of the framework: quartz 2.65, calcite 2.71, dolomite 2.87, g/cm³ Reservoir engineering · Porosity density of the mineral matrix (grains): about 2.65 g/cm³ for quartz, 2.71 for calcite, 2.87 for dolomite, g/cm³ Drilling · Pore pressure and overburden pressure ρ m a , ρ f \rho_{ma},\ \rho_f ρ ma , ρ f ρ o \rho_o ρ o ρ o , ρ w \rho_o,\ \rho_w ρ o , ρ w ρ r \rho_r ρ r ρ s \rho_s ρ s density of the particle; for quartz 2650, kg/m³ Geoscience · Sediment texture: grain size, sorting and shape density of the salt, about 2160, kg/m³ Geoscience · Folds, salt diapirs and their relationship to faults bulk density of the shale cuttings, g/cm³ Drilling · Abnormal formation pressures: origin, prediction and recognition density of the gas-cut mud measured at the outlet at atmospheric pressure, g/cm³ Drilling · Well control: primary barrier and kick indicators density of the mixture in the pipe, allowing for slip of the phases, kg/m³ Production · Multiphase flow in tubing density of the mixture in the pipe, allowing for slip (the actual density), kg/m³ Production · Multiphase flow in tubing ρ steel \rho_{\text{steel}} ρ steel density of steel, 7850 kg/m³, kg/m³ Drilling · Drill string: pipe, tool joints, drill collars and heavy-weight drill pipe density of steel, about 7850 kg/m³, kg/m³ Drilling · Casing: purpose, types, properties and standards density of steel, 7850 kg/m³, kg/m³ Production · Sucker-rod pumping ρ s w \rho_{sw} ρ s w ρ w \rho_w ρ w ρ w , ρ o \rho_w,\ \rho_o ρ w , ρ o densities of formation water and oil in the reservoir, kg/m³ Geoscience · Traps and timing densities of formation water and oil at reservoir conditions (for a gas accumulation, the gas density instead of ρ o \rho_o ρ o , kg/m³ Reservoir engineering · Fluid saturation densities of the collected water and of the stock-tank oil (oil with its gas removed), g/cm³ Reservoir engineering · Fluid saturation densities of water and oil, kg/m³ Reservoir engineering · Capillary pressure and the transition zone densities of formation water and oil at reservoir conditions, kg/m³ Reservoir engineering · Capillary pressure and the transition zone densities of water and oil at reservoir conditions, kg/m³ Well testing · Water and gas coning densities of water and oil in the formation, g/cm³ Well testing · Perched and tilted contacts, trapped water densities of water and oil: 1.0 and about 0.8, g/cm³ Drilling · Field testing of drilling fluids densities of water and oil at the water temperature, kg/m³ Production · Produced water: composition, treatment and disposal ρ w , ρ o , ρ g \rho_w,\ \rho_o,\ \rho_g ρ w , ρ o , ρ g σ \sigma σ sorting: the standard deviation of sizes; in practice, use σ I \sigma_I σ I , φ units Geoscience · Sediment texture: grain size, sorting and shape standard deviation of sizes, φ units Geoscience · Sediment texture: grain size, sorting and shape standard deviation of the natural logarithm of permeability about the line, — Geoscience · Reservoir quality: geological controls on porosity and permeability interfacial tension between the hydrocarbon and water (how strongly the boundary between the two fluids pulls on itself), N/m Geoscience · Reservoir and seal standard deviation, units of the quantity Geoscience · Distributions and sample size standard deviation of the natural logarithm of the quantity, — Geoscience · Distributions and sample size statistical error of one sample at the given logging speed (from the tool specification), curve units Logs and petrophysics · Log acquisition, processing and presentation interfacial (surface) tension, liquid–gas, mN/m Reservoir engineering · Oil viscosity and interfacial tension interfacial tension between the displacing and the displaced phase, N/m Reservoir engineering · Oil viscosity and interfacial tension interfacial tension, N/m Reservoir engineering · Capillary pressure and the transition zone standard deviation of the natural logarithm of permeability, — Reservoir engineering · Reservoir heterogeneity and permeability averaging error in finding the average pressure (standard deviation), MPa Reservoir engineering · History matching of aquifer parameters shape factor of the matrix blocks, m⁻² Simulation · Types of reservoir simulation model weight of the end of the step: 0 is the explicit scheme, 1 is the implicit scheme, ½ is the Crank–Nicolson scheme, — Simulation · Finite differences: from equations to computation weight of the scheme, — Simulation · Finite differences: from equations to computation oil–water interfacial tension, N/m Simulation · Pore-scale flow modelling yearly volatility, the standard deviation of the yearly push, fraction per year Economics · Market, financial and regulatory uncertainty σ ln k \sigma_{\ln k} σ l n k σ , θ \sigma,\ \theta σ , θ σ ′ \sigma' σ ′ σ 1 , σ 3 \sigma_1,\ \sigma_3 σ 1 , σ 3 σ 2 \sigma^2 σ 2 σ cos θ \sigma\cos\theta σ cos θ σ h , σ H \sigma_h,\ \sigma_H σ h , σ H σ H , σ h \sigma_H,\ \sigma_h σ H , σ h σ k \sigma_k σ k σ v \sigma_v σ v τ \tau τ thermal time constant of the lithosphere; about 63 million years for a a a , million years Geoscience · Plate tectonics and sedimentary basins tortuosity — the ratio of the length of the fluid path to the length of the sample, — Geoscience · Reservoir quality: geological controls on porosity and permeability bed shear stress of the flow, Pa Geoscience · Primary sedimentary structures shear stress on the plane, MPa Geoscience · Stress, strain and structural analysis shear stress on a plane, MPa Geoscience · Fractures and naturally fractured reservoirs time constant: in this time the pressure difference between the compartment and the neighbouring layer falls by a factor of e ≈ 2.72 e \approx 2.72 e ≈ 2.72 , s Geoscience · Reservoir architecture and performance trial shift, m Logs and petrophysics · Log acquisition, processing and presentation shear stress between the fluid layers, Pa Reservoir engineering · Oil viscosity and interfacial tension the moment to which the increase of the rate refers, s Reservoir engineering · Superposition principle time constant of the aquifer, d Reservoir engineering · Aquifer models: water influx time constant of the aquifer, c t W / J c_tW/J c t W / J , d Reservoir engineering · Simplified water influx models: Fetkovich and Carter–Tracy time constant: in this time the difference between the sandface rate and the wellhead rate falls by a factor of about e ≈ 2.7 \e \approx 2.7 e ≈ 2.7 , s Well testing · Wellbore storage duration of the short shut-in at the wellhead for running the valve, h Well testing · Nonideal wellbore storage, well clean-up and changing skin dimensionless time based on L 2 L^2 L 2 η \eta η , — Well testing · Semi-infinite systems: theory and test analysis time constant: it sets how fast the pressure approaches its steady value, s Well testing · Pressure measurement with the wireline formation tester time constant of the barrier: the step grows as 1 − e − t / τ 1 - e^{-t/\tau} 1 − e − t / τ 3 τ 3\tau 3 τ , d Well testing · Pressure measurements in producing reservoirs: barriers and accuracy time constant of the decline of the rate, d Well testing · Lumped multi-tank material balance model characteristic depletion time (the time scale of the pressure decline), d Simulation · What a reservoir simulation model is and why it is needed how much earlier the wave arrives from the near side (and later from the far side), s Drilling · Remedial cementing, cement plugs and cement evaluation shear stress, Pa Drilling · Drilling fluid rheology and flow regimes φ \varphi φ grain size in phi units, — Geoscience · Sediment texture: grain size, sorting and shape trend of the line, ° Geoscience · Stress, strain and structural analysis angle of friction: t a n φ = μ \mathrm{tan}\,\varphi = \mu tan φ = μ friction on a plane ), ° Geoscience · Structural styles and tectonic history geographic latitude of the station, ° Geoscience · Geophysical exploration methods direction: the angle from the x x x y y y , ° Simulation · Special topics in upscaling angle of internal friction of the rock, ° Drilling · Bit selection and dull grading azimuth, the angle in the horizontal plane from the direction to the north to the direction to the point, clockwise, from 0 to 360°, degrees Drilling · Directional wells: applications and profile azimuth from the chosen north, degrees Drilling · Directional survey calculations angle of internal friction, ° Production · Sand production: types, prediction and cost of the problem volume fraction of residual water in the oil, fraction Production · Oil treating: separators, dehydration, desalting and stabilisation the share of the deviation that remains after a year: 1 is a random walk, less than 1 is mean reversion, — Economics · Market, financial and regulatory uncertainty ϕ \phi ϕ porosity of the mixture, fraction Geoscience · Sediment texture: grain size, sorting and shape porosity, fraction Geoscience · Reservoir quality: geological controls on porosity and permeability effective porosity, fraction Geoscience · Reservoir quality: geological controls on porosity and permeability mean porosity of the reservoir, fraction Geoscience · Volumetric estimation of hydrocarbons in place porosity, fraction Logs and petrophysics · Borehole environment: invaded zone and mudcake true porosity, fraction Logs and petrophysics · Neutron log porosity: the volume fraction of the pores that are filled with fluid, fraction Logs and petrophysics · Porosity from the sonic log porosity with a correction for the fluid, fraction Logs and petrophysics · Porosity from the sonic log porosity outside the shale material (effective), fraction Logs and petrophysics · Porosity from the neutron log porosity of the formation, fraction Logs and petrophysics · Gas, shale, carbonate and pressure effects on porosity logs porosity, fraction (in reports, %) Reservoir engineering · Porosity average open porosity, fraction Reservoir engineering · Porosity porosity (fraction), — Reservoir engineering · Rock permeability porosity of the sample, fraction Reservoir engineering · Capillary pressure and the transition zone porosity, fraction Well testing · Skin factor porosity of the pack, fraction Well testing · Inflow at high rates: non-Darcy flow porosity of the reservoir, fraction Well testing · Wellbore storage porosity of the rocks through which the contact has risen, — Well testing · Two-phase flow and reservoir description from formation-tester data porosity of the reservoir rock, fraction Simulation · Building a simulation model: input data and results porosity (the share of the rock volume taken up by pores), fraction Drilling · Pore pressure and overburden pressure porosity of the shale, fraction Drilling · Abnormal formation pressures: origin, prediction and recognition volume fraction of clay in the suspension, fraction Drilling · Water-based muds and clay chemistry porosity of the rock, fraction Drilling · Solids control in drilling fluids porosity, fraction Production · Acid systems and treatment design porosity of the rock: the dissolved mineral took the share ( 1 − ϕ ) (1 - \phi) ( 1 − ϕ ) , — Production · Acid treatment of carbonates and special wells Φ \Phi Φ ϕ , μ , c t \phi,\ \mu,\ c_t ϕ , μ , c t porosity, viscosity, total compressibility, —, Pa·s, 1/Pa Reservoir engineering · Diffusivity equation porosity, viscosity, total compressibility (constants), —, Pa·s, 1/Pa Simulation · Pressure equation for single-phase flow porosity, viscosity of the fluid at reservoir conditions, total compressibility, —, Pa·s, Pa⁻¹ Production · Inflow to a hydraulically fractured well ϕ , c t \phi,\ c_t ϕ , c t ϕ , c t , h \phi,\ c_t,\ h ϕ , c t , h porosity, total compressibility c w + c f c_w + c_f c w + c f , —, 1/MPa (1/Pa in t D t_D t D Reservoir engineering · Unsteady-state water influx: the van Everdingen–Hurst method porosity, total compressibility, thickness of the reservoir, —, 1/MPa, m Well testing · Type-curve matching porosity, total compressibility, reservoir thickness, —, 1/Pa, m Well testing · A sealing fault near the well: the method of images porosity, total compressibility, thickness, —, 1/Pa, m Well testing · Semi-infinite systems: theory and test analysis porosity, total compressibility and thickness of the tight unit, —, 1/Pa, m Well testing · Pressure measurements in producing reservoirs: barriers and accuracy ϕ 0 \phi_0 ϕ 0 ϕ 1 , ϕ 2 \phi_1,\ \phi_2 ϕ 1 , ϕ 2 φ 1 , φ 2 \varphi_1,\ \varphi_2 φ 1 , φ 2 ϕ c \phi_c ϕ c ϕ D \phi_D ϕ D φ g \varphi_{\text{g}} φ g ω \omega ω angular velocity of the relative rotation of the plates, rad/million years (degrees × π/180) Geoscience · Plate tectonics and sedimentary basins angle between the line of the section and the dip direction, ω = 90 ° − β \omega = 90° - \beta ω = 90° − β , ° Geoscience · Stress, strain and structural analysis acentric factor of the substance, — Reservoir engineering · Cubic equations of state acentric factor, — Reservoir engineering · Cubic equations of state exponent: 1 gives the arithmetic mean and −1 the harmonic mean; as ω → 0 \omega \to 0 ω → 0 , — Reservoir engineering · Reservoir heterogeneity and permeability averaging over-relaxation parameter, 1 < ω < 2 1 < \omega < 2 1 < ω < 2 , — Simulation · Solving systems of linear equations in simulators angular velocity, 2 π n / 60 2\pi n/60 2 π n /60 n n n , rad/s Simulation · Petrophysical input for simulation: relative permeability and capillary pressure rotary speed of the cone relative to the bit body, rpm Drilling · Drill bits: types and design toolface from the high side, clockwise, degrees Drilling · Deflection tools and downhole motors toolface at the start of the interval, from the high side clockwise, degrees Drilling · Deflection tools and downhole motors gravity toolface, measured clockwise from the high side of the hole, looking down the hole; the quadrant follows from the signs of G y G_y G y − G x -G_x − G x , degrees Drilling · Survey instruments: magnetic, gyroscopic and inertial angular frequency, 2 π f 2\pi f 2 π f , 1/s Drilling · Measurement while drilling angular velocity of the crank, π n / 30 \pi n/30 π n /30 , rad/s Production · Sucker-rod pumping angular velocity, rad/s Production · Progressing cavity pumps and hybrid systems