Skin pressure drop and flow efficiency
Additional pressure drop near the well due to skin, flow efficiency, damage ratio, and the actual and undamaged productivity index — how much the rate would grow if the skin were removed.
ΔP_s = (2 / ln 10) · m · s = 0.869 · m · sFE = (P̄ − P_wf − ΔP_s) / (P̄ − P_wf), DR = 1 / FEJ = q / (P̄ − P_wf), J₀ = q / (P̄ − P_wf − ΔP_s)Skin adds a pressure drop at the wellbore wall ΔP_s = q · B · μ · s / (2π · k · h), which is 0.869 · m · s in terms of the slope. FE < 1 means a damaged well (DR > 1), FE > 1 a stimulated one. The potential assumes the same drawdown and the same resistance of the rest of the reservoir; below the bubble point it is an approximation.
Source: Skin factor: van Everdingen (1953), Hurst (1953); Earlougher, SPE Monograph 5 (1977), ch. 5; Lee, Well Testing (1982)
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
From the build-up (P* or P̄) or a static survey.
Before the shut-in for the build-up.
Unit converter for this formulaSemilog slope · Pressure · Liquid rate · Productivity index · Fraction and percent
- MPa/cycle1
- kPa/cycle1,000
- bar/cycle10
- (kgf/cm²)/cycle10.1972
- psi/cycle145.038
Pressure change per log cycle of time.
- FE — Flow efficiency–
- DR — Damage ratio–
- J — Actual productivity index–
- J₀ — Productivity index without skin–
- q₀ — Rate without skin at the same drawdown–
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.