Geomechanics and FracturingIn-Situ Stress and Rock Mechanics

Shale Compaction Formula

\phi_e=\phi e^{-\beta_s\sigma_v}

Shale Compaction calculates compacted shale porosity for in-situ stress and rock mechanics workflows in geomechanics and fracturing.

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How engineers use this formula

Use this formula when the listed inputs (phi, beta_s, sigma_v) 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, phi_e equals 0.234612 fraction.

phifraction

0.35

beta_s1/MPa

0.02

sigma_vMPa

Inputs

phi

fraction

Porosity

beta_s

1/MPa

Empirical Compaction Constant

sigma_v

MPa

Vertical Effective Stress

Outputs

phi_e

fraction

Compacted Shale Porosity

phi

fraction

Porosity

beta_s

1/MPa

Empirical Compaction Constant

sigma_v

MPa

Vertical Effective Stress

Source and review

reviewed

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

Zoback, M.D. 2007. Reservoir Geomechanics. Cambridge University Press, Page 46.

Source