Eaton Pore Pressure Gradient from Resistivity Ratio Formula
Eaton Pore Pressure Gradient from Resistivity Ratio calculates pore pressure gradient for in-situ stress and rock mechanics workflows in geomechanics and fracturing.
How engineers use this formula
Use this formula when the listed inputs (Gob, Gnp, Ro, Rn, TVD) 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, Gpp equals 0.767128 psi/ft.
1
0.465
1.5
3
10000
Inputs
Gob
psi/ftOverburden Gradient
Gnp
psi/ftNormal Pore Pressure Gradient
Ro
ohm-mObserved Shale Resistivity
Rn
ohm-mNormal Trend Shale Resistivity
TVD
ftTrue Vertical Depth
Outputs
Gpp
Pore Pressure Gradient
Pp
Pore Pressure
R_ratio
Observed-to-Normal Resistivity Ratio
Ro
Observed Shale Resistivity
TVD
True Vertical Depth
Source and review
reviewedPore pressure prediction while drilling using modified Eaton's equations, Abbas, R.K., Hamad, F.A., Mahmood, S.M. (2021)
Abbas, R.K. et al. 2021. Pore pressure prediction while drilling using modified Eaton's equations. Journal of Petroleum Exploration and Production Technology.
Source