PetrophysicsResistivity Logs
Formation Factor - Archie's Equation Formula
Formation Factor - Archie's Equation calculates formation factor for resistivity logs workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (T, phi) are known and the assumptions behind the cited resistivity logs 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, F equals 7.5 dimensionless.
Tdimensionless
1.5
phifraction
0.2
Inputs
T
dimensionlessTortuosity Factor
phi
fractionPorosity
Outputs
F
dimensionless
Formation Factor
T
dimensionless
Tortuosity Factor
phi
fraction
Porosity
Source and review
reviewedEllis, D.V., Singer, J.M. 2008. Well Logging for Earth Scientists, Second Edition, Chapter 4, Page 76.
Source