PetrophysicsElectrical Properties
Formation Water Resistivity from Resistivity Ratio Method Formula
Formation Water Resistivity from Resistivity Ratio Method calculates formation water resistivity for electrical properties workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (R_t, R_xo, R_mf) are known and the assumptions behind the cited electrical properties 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, R_w equals 1 ohm m.
R_tohm m
20
R_xoohm m
5
R_mfohm m
0.25
Inputs
R_t
ohm mTrue Formation Resistivity
R_xo
ohm mFlushed-Zone Resistivity
R_mf
ohm mMud Filtrate Resistivity at Formation Temperature
Outputs
R_w
ohm m
Formation Water Resistivity
R_t
ohm m
True Formation Resistivity
R_xo
ohm m
Flushed-Zone Resistivity
R_mf
ohm m
Mud Filtrate Resistivity at Formation Temperature
Source and review
reviewedAAPG Wiki. Water resistivity determination, resistivity ratio method.
Source