Stress Polygon Calculator

Estimation of the state of stress
 

The stress polygon (Zoback, M., 2007, "Reservoir Geomechanics"), allows the estimation of the stress state for a given set of observations from image logs, pore pressure, vertical stress, minimum horizontal stress Shmin, and mechanical properties. Once we get an idea of the possible ranges of stress anisotropy, we can use this information to calibrate a given fracture geometry with effective permeability measurements at the well. Use the effective fracture permeability anisotropy calculator to do this.

 

Input:

  • Vertical stress Sv

  • Pore pressure

  • Effective UCS (Unconfined compressive strength) of your rock (from tabulated values in the literature) 

  • Coefficient of sliding friction

  • Delta P: mud weight - pore pressure. Additional pore pressure from drilling mud weight.

  • Observations from image logs regarding the presence (or not) of tensile fractures and borehole breakouts (y -yes, n -no, NA - not available)

  • Measured minimum horizontal stress (Shmin)

  • Units: any pressure or pressure gradient units, as long as you use the same for all parameters (use our units converter if needed)

  • Depth: for conversion between pressure and pressure gradient units

 

Assumptions: 

Rock tensile strength is zero;  thermal stresses are zero; width of borehole breakouts at the compressive failure line is zero (setting this value to 0 means that no wellbore breakouts are observed below the compressive failure line).

 

Output:

  • Stress polygon for a given set of parameters

  • Estimated range of possible horizontal stress anisotropy for a given Shmin

  • Tensile failure line (if drilling induce tensile fractures are observed, the stress state is above this line)

  • Compressive failure line (if borehole breakouts are observed, the stress state is above this line)

  • Vertical stress (Sv) line

  • Measured Minimum Horizontal stress (Shmin) line

  • Possible Maximum Horizontal stress state line (Shmax)

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  • This calculator is not designed to work on mobile devices