Flushed-Zone Water Saturation from Formation Factor Formula
Flushed-Zone Water Saturation from Formation Factor calculates flushed-zone water saturation for resistivity logs workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (F, R_mf, R_xo, n) 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_xo equals 0.790569 fraction.
25
0.25
10
2
Inputs
F
dimensionlessFormation Resistivity Factor
R_mf
ohm mMud Filtrate Resistivity at Formation Temperature
R_xo
ohm mFlushed-Zone Resistivity from Shallow Investigation Log
n
dimensionlessSaturation Exponent
Outputs
S_xo
Flushed-Zone Water Saturation
F
Formation Resistivity Factor
R_mf
Mud Filtrate Resistivity at Formation Temperature
R_xo
Flushed-Zone Resistivity
n
Saturation Exponent
Source and review
reviewedWater resistivity determination, AAPG Wiki
AAPG Wiki. Water resistivity determination, invaded-zone Archie relation and formation-factor saturation form.
Source