Geomechanics and FracturingIn-Situ Stress and Rock Mechanics

Twisting Stress Around a Vertical Wellbore Formula

\tau=\frac{1}{2}(S_{hmax}-S_{hmin})\left(1+\frac{2R^2}{r^2}-\frac{3R^4}{r^4}\right)\sin(2\theta)

Twisting Stress Around a Vertical Wellbore calculates twisting stress 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_hmax, S_hmin, R, r, theta) 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, tau_twist equals 1,182.22237 psi.

S_hmaxpsi

8000

S_hminpsi

6000

Rft

0.33

rft

thetarad

0.7853981633974483

Inputs

S_hmax

psi

Maximum Horizontal Stress

S_hmin

psi

Minimum Horizontal Stress

R

Wellbore Radius

r

Radial Position from Wellbore Center

theta

rad

Azimuth from Maximum Horizontal Stress Direction

Outputs

tau_twist

psi

Twisting Stress

S_hmax

psi

Maximum Horizontal Stress

S_hmin

psi

Minimum Horizontal Stress

Source and review

reviewed

Zoback, M.D. 2007. Reservoir Geomechanics, Cambridge University Press, Page 170.

Source