Geomechanics and FracturingIn-Situ Stress and Rock Mechanics

Pore Pressure of Shale Flemings Formula

P_p=S_v-\frac{1}{\beta_c}\ln\left(\frac{\phi_o}{\phi}\right)

Pore Pressure of Shale Flemings calculates pore pressure 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 (S_v, beta_c, phi_o, phi) 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, P_p equals 6,824.990927 psi.

S_vpsi

8000

beta_c1/psi

0.0004

phi_ofraction

0.4

phifraction

0.25

Inputs

S_v

psi

Vertical Stress

beta_c

1/psi

Compressibility Coefficient

phi_o

fraction

Initial Porosity

phi

fraction

Porosity from Sonic Log

Outputs

P_p

psi

Pore Pressure

S_v

psi

Vertical Stress

beta_c

1/psi

Compressibility Coefficient

phi_o

fraction

Initial Porosity

phi

fraction

Porosity from Sonic Log

Source and review

reviewed

Reservoir Geomechanics, Zoback, M.D. (2007)

Zoback, M.D. 2007. Reservoir Geomechanics. Cambridge University Press, Page 48.

Source