PetrophysicsResistivity Logs
Equivalent Formation Water Resistivity from SP Formula
Equivalent Formation Water Resistivity from SP calculates equivalent formation water resistivity for resistivity logs workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (R_mfe, SSP, T_F) 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, R_we equals 0.114295 ohm m.
R_mfeohm m
1
SSPmV
-75
T_FdegF
140
Inputs
R_mfe
ohm mEquivalent Mud Filtrate Resistivity at Formation Temperature
SSP
mVStatic Spontaneous Potential Deflection
T_F
degFFormation Temperature
Outputs
R_we
ohm m
Equivalent Formation Water Resistivity
K_sp
mV
SP Temperature Coefficient
Source and review
reviewedWater resistivity determination, AAPG Wiki
AAPG Wiki. Water resistivity determination, SP method, standard SSP equation and temperature coefficient.
Source