Geomechanics and FracturingIn-Situ Stress and Rock Mechanics

Minimum Mud Pressure to Avoid Wellbore Breakout Formula

P_{Wshear}=P_p+\frac{3\sigma_{Hmax}-\sigma_{hmin}-UCS}{1+q}

Minimum Mud Pressure to Avoid Wellbore Breakout calculates minimum wellbore pressure to avoid breakout 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, P_p, UCS, mu_i, 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, P_Wshear equals 4,279.195484 psi.

S_Hmaxpsi

6300

S_hminpsi

4300

P_ppsi

3080

UCSpsi

3500

mu_idimensionless

0.6

TVDft

7000

Inputs

S_Hmax

psi

Total Maximum Horizontal Stress

S_hmin

psi

Total Minimum Horizontal Stress

P_p

psi

Pore Pressure

UCS

psi

Unconfined Compressive Strength

mu_i

dimensionless

Internal Friction Coefficient

TVD

True Vertical Depth

Outputs

P_Wshear

psi

Minimum Wellbore Pressure to Avoid Breakout

MW_shear

ppg

Equivalent Mud Density for Breakout Limit

Source and review

reviewed

Introduction to Energy Geomechanics, Espinoza, D.N.

Espinoza, D.N. Introduction to Energy Geomechanics, Chapter 6.3, Eq. 6.9.

Source