PetrophysicsElectrical Properties
Archie True Formation Resistivity Formula
Archie True Formation Resistivity calculates true formation resistivity for electrical properties workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (R_w, phi, m, S_w, n) are known and the assumptions behind the cited electrical 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, R_t equals 5 ohm m.
R_wohm m
0.05
phifraction
0.2
mdimensionless
2
S_wfraction
0.5
ndimensionless
2
Inputs
R_w
ohm mFormation Water Resistivity
phi
fractionPorosity
m
dimensionlessCementation Exponent
S_w
fractionWater Saturation
n
dimensionlessSaturation Exponent
Outputs
R_t
ohm m
True Formation Resistivity
R_w
ohm m
Formation Water Resistivity
S_w
fraction
Water Saturation
phi
fraction
Porosity
Source and review
reviewedHartmann, D.J. and Beaumont, E.A. AAPG Wiki. Archie equation.
Source