A new approach to determine geomechanical parameters of Vertical Transverse Isotropic media using VSP data

• A new elliptical model was developed to predict onset of sanding.
• Shear failure was assumed to be the dominant cause of sand production.
• A new parameter c was introduced to determine changes in the borehole shape.
• Three well known failure criteria were used to develop the equation.
• Mogi–Coulomb based equations indicated a better performance compared to others.

Conventionally, high frequency Dipole Shear sonic Imager (DSI) logs are used for anisotropic modeling where fast and slow shear wave's velocities are required. However, the results obtained from a DSI log are restricted to a specific and possibly short interval of the wellbore. The aims of this paper are to use Vertical Seismic Profile (VSP) data and show its application in geomechanical analysis of subsurface layers under anisotropic condition. After processing and separating upgoing and downgoing P- and S-waves, a methodology based Vertical Transverse Isotropic (VTI) condition was presented to determine elastic stiffness parameters. Having stiffness parameters determined, elastic modulus, strength and in-situ stress parameters were estimated and calibrated against the field and core sample data. Although the VSP based geomechanical parameters were calibrated against the real field data, the accuracy of the method cannot be as much as that of the well logs. However, the method presented in this paper may become a very good asset for geomechanical evaluation of the intervals where well log data are not available.

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