Skin factor from a pressure build-up curve
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)Unit inconsistencies in the original: the page says Rw is entered in inches and converted to feet, but the conversion (Rw / 12) is disabled in the code, so Rw is used as entered; φ is given in %, while the formula expects a fraction; the constant C₂ = 3.0923 corresponds to metric units (k in mD, μ in mPa·s, Ct in 1/bar, Rw in m), for the field units listed here it is 3.2275. The calculation is kept as in the original.
Inputs
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Unit converter for this formulaPressure · Semilog slope · Permeability · Viscosity · Compressibility · Length · Fraction and percent
- MPa1
- kPa1,000
- bar10
- atm9.86923
- kgf/cm²10.1972
- mmHg7,500.62
- MPa(g)0.898675
- barg8.98675
- psi145.038
- psia145.038
- psig130.342
- ksi0.145038
psi and psia are absolute pressure; gauge units (barg, MPa(g), psig) are above atmospheric (101.325 kPa = 14.696 psi). Pressure differences in the formulas do not depend on this.
More in Build-up and drawdown
Skin factor from the semilog straight line of a pressure drawdown curve.
Slope m of the semilog straight line of a pressure build-up (+) or drawdown (−) curve, in psi per log cycle.
Slope m of the semilog straight line of a pressure build-up (+) or drawdown (−) curve, in bar per log cycle.
Transmissibility kh/μ, flow capacity kh and permeability from the slope of the semilog straight line of a build-up or drawdown (radial flow).
Effective 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.
Results 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.