Assessment of the influence of hydraulic and mechanical anisotropy on the fracture initiation pressure in permeable rocks using a complex potential approach

Abstract

This work aims at studying the fracture initiation pressure of a horizontal wellbore drilled in an anisotropic poroelastic medium based on an analytical model. Using the complex potential approach, the closed-form solution of stresses in the surrounding formation is deduced as a function of the orientation in respect with stratification and the pressure inside wellbore. The analytical solution is developed for the steady state flow in a permeable formation due to the difference between pressures applied at well wall and the pore pressure at the far-field. Once the stress distribution on the borehole wall is obtained, it is possible, by using a known anisotropic tensile strength criterion for the rock, to infer the explicit expression of the fracture initiation pressure as a function of different parameters, such as the anisotropic poroelastic properties, the anisotropic initial stresses, the bedding dip angle and the anisotropic tensile strength of the formation. The validation of the analytical is conducted by comparing it with the numerical results using the finite element method. Finally, through the parametric study, we highlight the influence of different factors on the fracture initiation pressure.