Archie Water Saturation from Resistivity Logs Calculator
Enter porosity, formation-water resistivity, true formation resistivity, and Archie constants. The calculator returns water saturation.
Calculation context and source notes
Archie water saturation estimates formation water saturation from resistivity-log measurements, porosity, formation-water resistivity, and Archie exponents.
Use it in clean sandstone or carbonate petrophysics workflows where Archie assumptions are appropriate, and calibrate formation-water resistivity plus the Archie exponents against local water, core, or log evidence where possible.
Solves for
S_w (fraction)
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Formula, variables, and sourceRelated source-backed guides
Formula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns S_w = 0.25 fraction. Defaults demonstrate the implementation; they are not recommended field values.
1
0.2
2
0.05
20
2
Input definitions
a
dimensionlessTortuosity Factor
phi
fractionPorosity
m
dimensionlessCementation Factor
R_w
ohm mFormation Water Resistivity
R_t
ohm mTrue Formation Resistivity
n
dimensionlessSaturation Exponent
Output definitions
S_w
Water Saturation
a
Tortuosity Factor
phi
Porosity
m
Cementation Factor
R_w
Formation Water Resistivity
R_t
True Formation Resistivity
n
Saturation Exponent
Engineering use, assumptions, and limits
Use it in clean sandstone or carbonate petrophysics workflows where Archie assumptions are appropriate, and calibrate formation-water resistivity plus the Archie exponents against local water, core, or log evidence where possible.
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.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
Core Laboratories. 2005. Formation Evaluation and Petrophysics, Page 45.
Open source reference