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Petroleum geoscience

Geoscience answers the first questions of any project: whether there is oil or gas in the subsurface, where exactly, in what rock and in what quantity.

The sections run from the structure of the Earth and sedimentation to the petroleum system and traps, then to geophysics, correlation and maps, and end with the estimation of hydrocarbons in place and reserves, with allowance for uncertainty.

39 / 39 topicsWhere to start: Structure and composition of the Earth

The Earth and rocks

  1. 01Structure and composition of the EarthCrust, mantle and core, lithosphere and asthenosphere: the composition, density and temperature of each layer and how seismic waves reveal them; isostasy; heat flow, radiogenic heat and temperature at depth — and why the lithosphere and the sedimentary cover matter to the petroleum geologist. Basic
  2. 02Minerals and rocksThe main rock-forming minerals and how to recognise them by hardness, cleavage, lustre, density and reaction with acid; the structure of silicates; igneous, sedimentary and metamorphic rocks and the rock cycle; which rocks serve as reservoirs and seals, and which minerals complicate drilling, logging and formation treatment. Basic
  3. 03Plate tectonics and sedimentary basinsLithospheric plates, how fast they move and how that is measured; divergent, convergent and transform boundaries and the Wilson cycle; rifts, passive margins, foreland basins, intracratonic basins and strike-slip basins — why each one subsides (stretching and cooling of the lithosphere, flexure under load) and why basins contain oil; the basins of Kazakhstan. Basic
  4. 04Stratigraphy and geologic timeThe principles of stratigraphy and the order of events in a section; unconformities and missing time; relative and numerical age — radioactive decay, dating of ash beds by zircon, isochrons; the geologic time scale, with boundary ages taken from the current international scale; litho-, bio- and chronostratigraphy, sea level and the basics of sequence stratigraphy; unconformities in the subsurface of Kazakhstan. Basic

Sedimentary rocks and environments

  1. 05Sedimentary rocks and their classificationClasses of sedimentary rock by mode of formation; names of clastic rocks by grain size and of sandstones by framework composition and matrix content (arenites and wackes, and the QFL triangle of quartz, feldspars and lithic fragments); carbonates after Dunham and Folk; dolomitic limestones and marls; evaporites and how much salt seawater yields; siliceous and biogenic rocks — and what a rock's name tells you about reservoir, seal and source rock. Basic
  2. 06Sediment texture: grain size, sorting and shapeGrain size on the Udden–Wentworth grade scale and in φ units; sieve, laser and sedimentation analysis; the Folk–Ward statistics — mean size, sorting, skewness; grain shape, sphericity and roundness, packing and framework — and how the texture of a sediment sets its initial porosity and permeability. In Russian-language petrography all of this is called the structure of the rock. Basic
  3. 07Reservoir quality: geological controls on porosity and permeabilityDeposition and burial: how grain size, sorting and shape and the clay matrix set the initial porosity and permeability; kaolinite, illite, chlorite and smectite in the pores — coats, pore fill, bridges; compaction, quartz and carbonate cement, dissolution and intergranular volume — what took the porosity away; the porosity–permeability relationship and its pitfalls; rock types by flow zone indicator (FZI) and Winland radius; prediction of quality away from wells; the Jurassic sandstones of South Mangyshlak. Intermediate
  4. 08Primary sedimentary structuresBeds and laminae; bedforms — ripples, dunes, plane bed, antidunes — as a function of flow velocity and grain size, and the cross-bedding they leave behind; structures made by waves and wind, graded beds and turbidites, sole marks, soft-sediment deformation and bioturbation; palaeocurrents, way-up indicators and how these structures look on core and borehole image logs. Intermediate
  5. 09Diagenesis: compaction, cementation and dissolutionStages and driving forces — effective stress, temperature, time and pore waters; diagenesis and catagenesis in Russian-language terms; mechanical compaction and the intergranular-volume curve, ductile grains and abnormal pressure; pressure solution and stylolites; quartz cement from a kinetic model — time spent in the hot zone, grain size and chlorite coats; carbonate cement and authigenic clays; dissolution of feldspars in closed and open systems; carbonate diagenesis and dolomitization; the arrival of oil and prediction of reservoir quality. Intermediate
  6. 10Facies, facies successions and sedimentary logsFacies as a description of a rock and as an interpretation of its environment; facies associations and successions; Walther's law and where it does not apply; fining-upward channel sandstones, coarsening-upward shoreface and delta front, turbidite successions; the graphic sedimentary log and gamma ray log motifs — bell, funnel, cylinder; the distribution of permeability through the thickness of a unit, and waterflooding; testing a succession with a transition matrix. Intermediate
  7. 11Continental environments: aeolian and fluvialDeserts, ergs, dunes and interdune lows; grainflow, grainfall and wind-ripple laminae, dune climbing and the thickness of cross-bed sets, permeability anisotropy across and along the wind; braided, meandering and anastomosing rivers, channel bars, oxbow lakes, levees, crevasse splays and alluvial fans; channel width and meander-belt width estimated from the thickness of the channel cycle, and the uncertainty of the estimate; fluvial reservoirs under waterflooding — Kumkol and the Jurassic of South Mangyshlak. Intermediate
  8. 12Coastal, shallow-marine and deep-marine environmentsZones from the shoreline to the basin floor and coast classes by tidal range; river-, wave- and tide-dominated deltas — distributary channels, mouth bars, interdistributary bays, growth faults; beaches, strandplains and the width of a coastal sand sheet from the sand budget; barrier islands and tidal inlets; tidal flats, estuaries and incised valleys; storm sands of the shelf and flooding surfaces; channels, levees and lobes of submarine fans, channel axis and margin from the amalgamation ratio; body dimensions against well spacing; the Caspian Sea, the Ural River delta, Kumkol, Mangyshlak and the Pre-Caspian Basin. Intermediate
  9. 13Carbonate sediments, environments and carbonate porosityThe carbonate factory — light, depth, warmth and water clarity; carbonate grains and minerals — aragonite, calcite, dolomite — and why mineralogy decides the fate of the pores; environments from sabkha and lagoon to reef, slope and basin; ramp, rimmed shelf and isolated platform; pore types after Choquette–Pray, separate and touching vugs and what they mean for permeability, logs and saturation; the subsalt carbonate buildups of the Pre-Caspian Basin. Intermediate

Petroleum system and traps

  1. 14Petroleum system and the play conceptThe elements and processes of a petroleum system, the critical moment and the events chart, play, lead and prospect, the play fairway and the geological chance of success. Basic
  2. 15Reservoir and sealWhat makes a rock a reservoir and what its quality depends on, which rocks act as seals and how tall a hydrocarbon column a seal can hold: entry pressure against buoyancy, capillary breakthrough and hydraulic fracturing. Intermediate
  3. 16Source rocks, maturation and migrationWhere organic matter is preserved, kerogen types, TOC and pyrolysis, maturation from the Arrhenius law and from vitrinite reflectance, the oil and gas windows, primary and secondary migration, and what happens to oil in the accumulation. Intermediate
  4. 17Traps and timingCrest, closure and spill point; structural, stratigraphic and hydrodynamic traps; tilted contacts and burial curves — and why the trap must exist before migration. Intermediate
  5. 18Geological risk and chance of successWhich event's probability is assessed for each element of a play; the product of probabilities and conditional probabilities, play risk and common risk segments, dependent prospects and updating the chances after a well, commercial success and risked volume — and what the chance of success does and does not mean. Intermediate

Structural geology

  1. 19Stress, strain and structural analysisStress and strain in geology: stresses on a plane, the Mohr circle and the role of pore pressure in slip on fractures, extension, shear and strain rate; brittle and ductile behaviour of rocks and the brittle–ductile transition; strike and dip and how they are recorded, true and apparent dip, bed thickness in vertical and deviated wells; structure contours, the three-point problem, cross-sections and vertical exaggeration; stereographic projection; cleavage, boudinage and stylolites. Intermediate
  2. 20FaultsNormal faults, reverse faults, thrusts and strike-slip faults and their relationship to stress; slip along the fault plane, throw and heave; missing and repeated section in wells and throw from the missing interval; faults on maps and the power law for faults below seismic resolution; the fault zone as a barrier or a conduit; sealing by juxtaposition and by fault rock — the Allan diagram, the shale gouge ratio (SGR) and the height of the column held; faults in traps and in field development. Intermediate
  3. 21Folds, salt diapirs and their relationship to faultsElements and classification of folds — limbs, hinge, axial surface, crest, interlimb angle, hinge plunge; axis and axial plane from the attitude of the limbs and the shift of the crest with depth; buckling and bending, bedding-parallel slip and extension in the crest; folds as traps; salt tectonics — why salt flows; pillows, domes, diapirs, minibasins and salt welds; traps at salt; the subsalt and suprasalt structural tiers of the Pre-Caspian Basin; folds above thrusts, fault-adjacent anticlines, drape folds and inversion folds, the folds of Mangyshlak. Intermediate
  4. 22Fractures and naturally fractured reservoirsExtension, shear and hybrid fractures: when and why a rock cracks — the Mohr circle, the Griffith envelope, pore pressure; fractures in folds, near faults and during uplift; fracture sets, linear intensity and spacing, the mechanical layer, the Terzaghi correction; aperture and the cubic law, the permeability of a fracture network and its decline as pressure falls, critically stressed fractures; types of naturally fractured reservoir and the consequences for development; fractures on core and image logs; Tengiz, Kashagan, South Mangyshlak. Intermediate
  5. 23Structural styles and tectonic historyStructural styles of extension, compression, strike-slip, inversion and salt flow: domino blocks and listric faults, rifts and transfer zones, fold-and-thrust belts, thrust imbricates and duplexes, Riedel shears, en echelon folds and flower structures, inversion anticlines and the null point; extension estimated from block rotation; how the tectonic history is reconstructed — cross-cutting relationships, unconformities, growth strata and the expansion index — and whether the trap was in place when the oil arrived; the South Turgai Basin and Mangyshlak. Intermediate
  6. 24Practical structural geologyWhat each source of structural data can show and what a map is fit for — fold curvature and data spacing; the dip plot of a well: domains, unconformities, bends near faults; pressure cells and the centroid effect — pressure at the crest of an isolated bed and the limit of the accumulation set by hydraulic fracturing of the seal; fractures and stress — directional permeability during depletion and injection; section balancing — bed length, excess area, depth to detachment and the area–depth line. Advanced

Geophysics and seismic surveying

  1. 25Geophysical exploration methodsWhy geophysics is needed and which rock property each method sees; gravity surveying — the anomaly over a buried body, a salt dome as a sphere, depth from the half-width, corrections and the Bouguer anomaly; magnetic surveying and depth to basement; seismic surveying: two-way time, velocity, depth and the false uplift beneath salt; electrical methods and magnetotellurics (MT); land, marine, airborne and satellite surveys; non-uniqueness and the integration of methods; geophysics in Kazakhstan — from variometers in the Emba region to the subsalt fields. Basic
  2. 26Seismic waves, acoustic impedance and reflectionsCompressional and shear waves in rocks and how gas changes one and hardly affects the other; wavelength; acoustic impedance and reflection coefficient — why density matters too; reflected energy; the Ricker wavelet, zero-phase and minimum-phase wavelets and polarity; the convolutional model and the synthetic seismogram from logs; tuning thickness and thin beds — time versus amplitude; absorption and the quality factor Q; a short note on AVO and bright spots. Intermediate
  3. 27Seismic acquisition and processingExplosives, vibrators and air guns, geophones, hydrophones and ocean-bottom nodes; the waves on a seismic gather and noise; the common-midpoint (CMP) method — offset, spread, fold and bin; 2D lines and 3D surveys, what a minimal 2D programme gives over a large area and what a survey costs; the processing flow — static corrections, deconvolution, velocity analysis, normal-moveout correction and stacking, time and depth migration; the Fresnel zone and bin size. Intermediate
  4. 28Seismic interpretationThe interpretation workflow; tying reflections to wells — check-shot survey, VSP, synthetics and sonic-log drift; horizon tracking and mis-ties at line intersections, faults on sections and time slices; time structure maps and time-to-depth conversion — average velocity, layer-cake model, linear velocity law, the Dix formula; traps and seismic facies; bright spots and flat spots and conformance with the structural contour; false structures and how velocity error carries over into closure and trap volume. Intermediate

Correlation and maps

  1. 29Well correlationLogs, core, cuttings, biostratigraphy and marker beds as correlation data and how to prepare them; lithostratigraphic and chronostratigraphic correlation and why joining “sand to sand” connects bodies that are not in communication; the structural panel and the panel flattened on a marker bed — growth of the structure; thicknesses in deviated wells (TVD, TVT, TST); graphic correlation and the line of correlation; faults, unconformities, facies changes and pinch-outs; “layer cake” or “jigsaw”. Intermediate
  2. 30Reservoir architecture and performanceReservoir bodies, how they stack and how they connect: the hierarchy of scales and flow units; sheets, belts, ribbons and lobes of different environments and their dimensions; “layer cake”, “jigsaw” and “labyrinth” architectures, the net-to-gross, dissection and lithological connectivity coefficients; connectivity and the percolation threshold — why a correlation panel underestimates connectivity; how much of the reservoir wells penetrate and how to orient waterflood rows; barriers, baffles and isolated compartments — pressure equilibration time; early water, wells that do not respond, unswept bodies; the Jurassic horizons of South Mangyshlak. Intermediate
  3. 31Structure maps and contouringContours and kinds of map — structure maps, isopach and isochore maps, net-thickness and property maps; the formation top in a deviated well from the directional survey, depths below sea level and absolute elevations, tying seismic to wells; contour interval and contouring by triangulation; mechanical, equal-spacing, parallel and interpretive contouring; gridding, inverse-distance weighting and minimum curvature on the same data; “bull's-eyes”, edge effects and other map errors. Basic
  4. 32Cross-sections from maps, map combination and faults on mapsA cross-section from a structure map: transferring contour intersections, apparent dip and vertical exaggeration; isochore and isopach maps as the difference between two surfaces and a base map from the top map plus isochores; faults on maps — fault cutoff lines, the fault polygon, fault-plane contours, offset contours and the throw profile; checking maps, sections and wells for consistency. Intermediate
  5. 33Gross rock volume from mapsThe area–depth curve and the gross rock volume above the contact: the trapezoidal and pyramidal rules, Simpson's rule and the “triangle” estimate; thick and thin beds — bottom water, outer and inner pool outlines, the edge-water zone, the geometric correction factor; crest, closure and spill point, contacts from wells (“oil down to”, “water up to”); how the volume changes with the contact, the map depths, the bed thickness and the way the map is constructed. Intermediate

Statistics, volumes and reserves

  1. 34Descriptive statistics in geologyThe histogram and the P10–P50–P90 percentiles, mean, median and mode, the three averages for permeability, standard deviation and coefficient of variation — and how to choose the right measure for core and log data. Basic
  2. 35Distributions and sample sizeNormal and log-normal distributions, the probability plot, the standard error of the mean, the number of samples needed for a given precision, and sampling bias, which no number of samples can correct. Intermediate
  3. 36Spatial correlation and the variogramThe experimental variogram from a row of wells; nugget effect, sill and range, trend and cyclicity; spherical, exponential and Gaussian models; covariance, correlogram and the effective number of independent data; anisotropy and the range ellipse; ordinary kriging — weights, declustering and estimation variance; sequential Gaussian simulation and the variogram in the geological model. Advanced
  4. 37Volumetric estimation of hydrocarbons in placeOil and gas initially in place from rock volume, net-to-gross ratio, porosity, saturation and formation volume factor — in metric and oilfield units; recoverable volumes and the recovery factor. Intermediate
  5. 38Probabilistic volumetrics by Monte Carlo simulationHow the distributions of the input parameters are turned into a distribution of volumes in place: drawing values with random numbers, the triangular distribution, dependence between parameters, the number of trials, the exceedance probability curve and the P90, P50 and P10 estimates — compared with deterministic cases and with a calculation from the mean values. Intermediate
  6. 39Classification of reserves and resourcesHow reserves differ from resources: the PRMS classes — reserves, contingent and prospective resources, the 1P, 2P and 3P categories and their probabilistic meaning, subclasses by project maturity and chance of commerciality; the national classification of Kazakhstan — categories A, B, C1 and C2 and resources C3, D0, D1 and D2, review by the State Reserves Commission (GKZ) and accounting, and what the categories mean for a contract and the signature bonus; one discovery from prospect to development decision in both systems, aggregation of estimates and reserves replacement. Intermediate

This section is growing: new topics are published after a technical review.