Skin Factor from Pressure Transient Semilog Analysis Formula
Skin Factor from Pressure Transient Semilog Analysis calculates skin factor for pressure transient analysis workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (Delta_p_1hr, m, k, phi, mu, c_t, r_w) are known and the assumptions behind the cited pressure transient analysis relationship match the engineering case being checked.
Assumptions
- Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
- The declared units match the field-unit constants used in the formula.
- The cited formula applies to the selected petroleum engineering workflow.
Limitations
- The calculation does not replace a full engineering model or operating procedure.
- Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.
Common mistakes
- Mixing unit systems without converting the inputs.
- Using default example values as field recommendations.
- Applying the formula outside the source assumptions.
Default example
Using the default inputs, s equals 1.356994 dimensionless.
500
80
50
0.2
2
0.00001
0.25
Inputs
Delta_p_1hr
psiPressure Change in the First Hour of the Test
m
psi/cycleSemilog Straight-Line Slope
k
mDEffective Permeability
phi
fractionPorosity
mu
cPFluid Viscosity
c_t
1/psiTotal Compressibility
r_w
ftWellbore Radius
Outputs
s
Skin Factor
Delta_p_1hr
Pressure Change in the First Hour of the Test
m
Semilog Straight-Line Slope
k
Effective Permeability
Source and review
reviewedAAPG Wiki, Pressure transient testing, oil-well skin-factor equation after W. John Lee.
Source