PetrophysicsResistivity Logs
Fertl-Hammack Shaly Sand Water Saturation Formula
Fertl-Hammack Shaly Sand Water Saturation calculates water saturation for resistivity logs workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (F, R_w, R_t, V_sh, phi_e, R_sh) 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, S_w equals 0.237388 fraction.
Fdimensionless
20
R_wohm m
0.08
R_tohm m
20
V_shfraction
0.15
phi_efraction
0.22
R_shohm m
3
Inputs
F
dimensionlessFormation Resistivity Factor
R_w
ohm mFormation Water Resistivity
R_t
ohm mTrue Rock Resistivity
V_sh
fractionBulk Volume Fraction of Shale
phi_e
fractionEffective Porosity
R_sh
ohm mShale Resistivity
Outputs
S_w
fraction
Water Saturation
Source and review
reviewedTheory, Measurement, and Interpretation of Well Logs, Bassiouni, Z. (1994)
Bassiouni, Z. 1994. Theory, Measurement, and Interpretation of Well Logs. SPE Textbook Series Vol. 4, Chapter 1, Page 16.
Source