Skin factor from a pressure drawdown curve
Skin factor from the semilog straight line of a pressure drawdown curve.
S = C₁ × ((Pi − P1hr) / m − log₁₀(k / (φ × μ × Ct × Rw²)) + C₂)The original page did not work: its button called sf_prc(), the build-up function, which reads a Pwf field that this page does not have, so no result was shown. Here Pi and P1hr take the place of the two pressures of sf_prc(), as in the displayed formula. As on the build-up page, Rw is used as entered (the inch-to-foot conversion is disabled in the code) and φ is given in %, although the formula expects a fraction.
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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 build-up 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.