Geomechanics and FracturingIn-Situ Stress and Rock Mechanics

Stress Perturbation Segall and Fitzgerald Formula

M=\alpha\frac{(1-2\nu)\pi H}{(1-\nu)8R}

Stress Perturbation Segall and Fitzgerald calculates stress perturbation 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 (alpha, nu, H, R) 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, M equals 0.020944 dimensionless.

alphadimensionless

0.8

nudimensionless

0.25

Hft

100

Rft

1000

Inputs

alpha

dimensionless

Stress Propagation Constant

nu

dimensionless

Poisson Ratio

H

Reservoir Height

R

Half the Lateral Extent

Outputs

M

dimensionless

Stress Perturbation

alpha

dimensionless

Stress Propagation Constant

H

Reservoir Height

R

Half the Lateral Extent

nu

dimensionless

Poisson Ratio

Source and review

reviewed

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

Zoback, M.D. 2007. Reservoir Geomechanics. Cambridge University Press, Page 112.

Source