Well test analysis
Build-up and drawdown interpretation: permeability and transmissibility from the slope, skin and the pressure drop near the well, radius of investigation, wellbore storage, gas well deliverability.
14 calculators
Build-up and drawdown
Skin factor from the semilog straight line of a pressure build-up curve.
S = C₁ × ((P1hr − Pwf) / m − log₁₀(k / (φ × μ × Ct × Rw²)) + C₂)Skin factor from the semilog straight line of a pressure drawdown curve.
S = C₁ × ((Pi − P1hr) / m − log₁₀(k / (φ × μ × Ct × Rw²)) + C₂)Slope m of the semilog straight line of a pressure build-up (+) or drawdown (−) curve, in psi per log cycle.
m = C × q × B × μ / (k × h)Slope m of the semilog straight line of a pressure build-up (+) or drawdown (−) curve, in bar per log cycle.
m = C × q × B × μ / (k × h)Transmissibility kh/μ, flow capacity kh and permeability from the slope of the semilog straight line of a build-up or drawdown (radial flow).
kh/μ = ln 10 / (4π) · q · B / m = 0.1832 · q · B / mEffective producing time before a build-up from the cumulative production and the last rate, the Horner time ratio (t_p + Δt)/Δt for the plot axis, and Agarwal's equivalent time.
t_p = 24 · N_p / qProductivity and skin
Test design
How far from the well the pressure transient has travelled during the test, and the hydraulic diffusivity: to choose the test duration and to judge whether the test will see the boundaries.
χ = k / (φ · μ · c_t)Wellbore storage coefficient from a moving liquid level and from fluid compression in a closed wellbore, and the time after which the build-up or drawdown reaches the semilog straight line of radial flow.
C = V_u / (ρ · g) + V_w · c_wHow many hours after a well starts at a constant rate the pressure begins to fall at the same rate throughout the drainage area: to plan drawdowns that reach the boundaries and reservoir limit tests.
t_pss = t_DA · φ · μ · c_t · A / kGas wells
Coefficients C and n of the gas deliverability equation q = C · (P̄² − P_wf²)ⁿ from two stabilized rates, and the absolute open flow, the rate at atmospheric bottomhole pressure.
q = C · (P̄² − P_wf²)ⁿThe flow coefficients a and b of the two-term equation P̄² − P_wf² = a · q + b · q² from two stabilized rates, and the absolute open flow — the standard way of interpreting gas well tests in Russian and Kazakh practice.
Δ = P̄² − P_wf² = a · q + b · q²Other areas
Total compressibility of the rock and its fluids from the saturations and the oil, water, gas and pore compressibilities, and the storativity φ·c_t: inputs to well test interpretation, radius of investigation and diffusivity.
c_t = S_o · c_o + S_w · c_w + S_g · c_g + c_fFrom Reservoir engineering and stimulationProductivity index from a stabilized rate and flowing bottomhole pressure, the drawdown, and the rate at another bottomhole pressure (straight-line IPR).
J = q / (P_res − P_wf)From Oil and gas productionResults are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.