Static Self Potential from NaCl Activities Formula
Static Self Potential from NaCl Activities calculates static self potential for electrical properties workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (t_Cl, R_gas, T_a, F_faraday, a_w, a_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, E_ssp equals 0.05018 V.
0.6
8.314
350
96485.336
0.05
0.2
Inputs
t_Cl
dimensionlessChlorine Anion Transference Number
R_gas
J/mol/KUniversal Gas Constant
T_a
KAbsolute Temperature
F_faraday
C/molFaraday Constant
a_w
dimensionlessNaCl Activity in Formation Water
a_mf
dimensionlessNaCl Activity in Mud Filtrate
Outputs
E_ssp
Static Self Potential
K_eq
Static SP Equilibrium Constant
t_Cl
Chlorine Anion Transference Number
T_a
Absolute Temperature
a_w
NaCl Activity in Formation Water
a_mf
NaCl Activity in Mud Filtrate
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 6, Pages 131-132.
Source