Shaly Sand Water Saturation Guide
A practical comparison of Indonesian, Archie, and Simandoux water-saturation calculations for resistivity logs, with input checks for shale volume, shale resistivity, porosity, and water resistivity.
linked formula references
verified source links
Practical workflow
- 1
Confirm whether the interval is sufficiently clean for Archie or needs an explicit shale-conductivity model.
- 2
Depth-match effective porosity, shale volume, true resistivity, water resistivity, and representative shale resistivity.
- 3
Run Indonesian and a comparison model with the same exponents and unit basis.
- 4
Reconcile model spread with core, capillary-pressure, production, and local log-interpretation evidence.
Choosing a saturation model
Start with the geology and log response, not with the calculator name. Archie is most defensible when the rock framework is effectively nonconductive. Indonesian and Simandoux relationships introduce shale conductivity in different empirical forms for shaly intervals.
Calculate more than one model on the same depth-matched inputs when the shale correction is uncertain. Differences between models are diagnostic; they should trigger review of shale volume, resistivity selection, porosity, mineralogy, invasion, and core evidence.
Input quality checks
Use fractional porosity and shale volume where the formula expects fractions. Correct formation-water and measured resistivity to a compatible temperature basis, and choose shale resistivity from representative wet shale rather than an arbitrary low-resistivity point.
Values outside the physical zero-to-one saturation interval indicate an input, unit, exponent, or model-applicability problem. Do not clip the result silently; diagnose the cause and document any interpretation adjustment.
Start with these calculators
These links keep the guide close to the working calculator flow.