Fracture Gradient - Zoback and Healy Calculator
Enter the stress and pressure terms required by the model. The calculator returns fracture gradient in the declared unit system.
Calculation context and source notes
Fracture gradient estimates the pressure gradient required to initiate or propagate a fracture under a stated stress model.
Use it for geomechanics screening, mud-window checks, and fracture-pressure comparisons before detailed wellbore stability work.
Solves for
S_hmin (psi)
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Formula, variables, and sourceFormula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns S_hmin = 5,602.857726 psi. Defaults demonstrate the implementation; they are not recommended field values.
0.6
9000
4000
Input definitions
mu_f
dimensionlessFriction Coefficient
S_v
psiVertical Stress
P_p
psiPore Pressure
Output definitions
S_hmin
Minimum Horizontal Stress
Engineering use, assumptions, and limits
Use it for geomechanics screening, mud-window checks, and fracture-pressure comparisons before detailed wellbore stability work.
Assumptions
- The selected stress model is appropriate for the local geologic setting.
- Input stress and pore-pressure values are representative at depth.
- Units are consistent across pressure and gradient terms.
Limitations
- Does not replace leak-off tests, mini-frac interpretation, or calibrated geomechanical models.
- Local depletion, anisotropy, natural fractures, and tectonic effects may change fracture pressure.
Common mistakes
- Using a generic stress model without local calibration.
- Mixing gradient and pressure units.
- Treating screening results as operational limits without review.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
Zoback, M.D. 2007. Reservoir Geomechanics, Cambridge University Press, Page 281.
Open source reference