PI Test Skin Factor and Average Permeability Formula
PI Test Skin Factor and Average Permeability calculates skin factor for inflow performance workflows in production engineering.
How engineers use this formula
Use this formula when the listed inputs (P, q, P_wf, k, B, h, mu, r_e, r_w) are known and the assumptions behind the cited inflow performance 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 17.318312 dimensionless.
3500
800
2500
100
1.2
50
1.5
1000
0.328
Inputs
P
psiAverage Reservoir Pressure
q
STB/dayFlow Rate
P_wf
psiWell Flowing Pressure
k
mDPermeability
B
RB/STBOil Formation Volume Factor
h
ftReservoir Thickness
mu
cPOil Viscosity
r_e
ftDrainage Radius
r_w
ftWellbore Radius
Outputs
s
Skin Factor
J
Productivity Index
k_j
PI-Test Average Permeability
q
Flow Rate
k
Permeability
B
Oil Formation Volume Factor
mu
Oil Viscosity
h
Reservoir Thickness
Source and review
reviewedLee, J., Rollins, J.B., and Spivey, J.P. 2003. Pressure Transient Testing, Vol. 9. Society of Petroleum Engineers, Page 16.
Source