PetrophysicsResistivity Logs
Archie Water Saturation from Resistivity Logs Formula
Archie water saturation estimates formation water saturation from resistivity-log measurements, porosity, formation-water resistivity, and Archie exponents.
How engineers use this formula
Use it in clean sandstone or carbonate petrophysics workflows where Archie assumptions are appropriate.
Assumptions
- The rock is sufficiently clean for Archie behavior.
- Formation-water resistivity and Archie exponents are representative.
- Input resistivities use consistent temperature correction and units.
Limitations
- Not appropriate for shaly sands without a shale correction model.
- Sensitive to cementation and saturation exponent choices.
Common mistakes
- Applying Archie directly to conductive shaly formations.
- Using uncorrected water resistivity.
- Assuming default Archie exponents are valid for every reservoir.
Default example
Using the default inputs, S_w equals 0.25 fraction.
adimensionless
1
phifraction
0.2
mdimensionless
2
R_wohm m
0.05
R_tohm m
20
ndimensionless
2
Inputs
a
dimensionlessTortuosity Factor
phi
fractionPorosity
m
dimensionlessCementation Factor
R_w
ohm mFormation Water Resistivity
R_t
ohm mTrue Formation Resistivity
n
dimensionlessSaturation Exponent
Outputs
S_w
fraction
Water Saturation
a
dimensionless
Tortuosity Factor
phi
fraction
Porosity
m
dimensionless
Cementation Factor
R_w
ohm m
Formation Water Resistivity
R_t
ohm m
True Formation Resistivity
n
dimensionless
Saturation Exponent
Source and review
reviewedCore Laboratories. 2005. Formation Evaluation and Petrophysics, Page 45.
Source