Cumulative Effective Compressibility – Fetkovich Formula
Cumulative Effective Compressibility – Fetkovich calculates cumulative effective compressibility for pvt and rock-fluid properties workflows in reservoir engineering.
How engineers use this formula
Use this formula when the listed inputs (S_wi, c_w, M, c_f) are known and the assumptions behind the cited pvt and rock-fluid properties 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, c_e equals 0.000009 1/psi.
0.25
3e-6
0.1
5e-6
Inputs
S_wi
fractionInitial Water Saturation
c_w
1/psiCumulative Total Water Compressibility
M
dimensionlessDimensionless Volume Ratio
c_f
1/psiTotal PV (Formation) Compressibility
Outputs
c_e
Cumulative Effective Compressibility
S_wi
Initial Water Saturation (rearranged)
c_w
Water Compressibility (rearranged)
M
Dimensionless Volume Ratio (rearranged)
c_f
Formation Compressibility (rearranged)
Source and review
reviewedAhmed, T., McKinney, P.D. (2005). Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter 3, Pages 215–216.
Source