Mody-Hale Osmotic Pore-Pressure Increase from Molar Volume Formula
Mody-Hale Osmotic Pore-Pressure Increase from Molar Volume calculates osmotic pore-pressure increase for in-situ stress and rock mechanics workflows in geomechanics and fracturing.
How engineers use this formula
Use this formula when the listed inputs (E_m, R_psi_L, T, V_w, A_p, A_m) are known and the assumptions behind the cited in-situ stress and rock mechanics 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, dP equals 2,086.439932 psi.
0.8
1.20591158
350
0.018
0.95
0.85
Inputs
E_m
dimensionlessMembrane Efficiency
R_psi_L
psi*L/(mol*K)Gas Constant
T
KTemperature
V_w
L/molMolar Volume of Water
A_p
dimensionlessPore Fluid Activity
A_m
dimensionlessMud Activity
Outputs
dP
Osmotic Pore-Pressure Increase
E_m
Membrane Efficiency
R_psi_L
Gas Constant
T
Temperature
V_w
Molar Volume of Water
A_p
Pore Fluid Activity
A_m
Mud Activity
Source and review
reviewedReservoir Geomechanics, Zoback, M.D. (2007)
Zoback, M.D. 2007. Reservoir Geomechanics. Cambridge University Press, Page 105.
Source