Geomechanics and FracturingIn-Situ Stress and Rock Mechanics

Modified Eaton Pore Pressure Gradient from Specific Energy Formula

G_{pp}=G_{ob}-(G_{ob}-G_{np})\left(\frac{SPE_o}{SPE_n}\right)^m

Modified Eaton Pore Pressure Gradient from Specific Energy calculates pore pressure gradient for in-situ stress and rock mechanics workflows in geomechanics and fracturing.

Calculate

How engineers use this formula

Use this formula when the listed inputs (Gob, Gnp, SPE_o, SPE_n, m_eaton, 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 0.5372 psi/ft.

Gobpsi/ft

Gnppsi/ft

0.465

SPE_opsi

6000

SPE_npsi

10000

m_eatondimensionless

0.2838

TVDft

10000

Inputs

Gob

psi/ft

Overburden Gradient

Gnp

psi/ft

Normal Pore Pressure Gradient

SPE_o

psi

Observed Specific Energy

SPE_n

psi

Normal Trend Specific Energy

m_eaton

dimensionless

Modified Eaton Specific-Energy Exponent

TVD

True Vertical Depth

Outputs

Gpp

psi/ft

Pore Pressure Gradient

Pp

psi

Pore Pressure

SPE_ratio

dimensionless

Observed-to-Normal Specific Energy Ratio

SPE_o

psi

Observed Specific Energy

TVD

True Vertical Depth

Source and review

reviewed

Pore 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