The thermal and chemical effect on wellbore strengthening treatment in shale formation

Abstract

The success rate of wellbore strengthening is relatively low in shales. Thus, a multi-field coupling wellbore strengthening model was developed by introducing the fully coupled thermo-chemo-poroelastic theory into wellbore strengthening physical model and the fracture element was added to study the closure process of isolated fracture in shales. The thermal and chemical effects were researched by observing the change of hoop stress and fracture aperture. Results show that thermal factor is crucial to wellbore strengthening. The preliminary treatment of wellbore strengthening is mainly controlled by adjusting thermal gradient, combined with a reasonable chemical gradient to inhibit hydration and swelling of clay. The anisotropic Young's modulus and Poisson's ratio are sensitive to hoop stress, the solute diffusion coefficient and permeability anisotropy have a minor effect on wellbore strengthening in low permeability formation. Compared with short fracture, the relatively longer fracture is beneficial for wellbore strengthening with bridging location near the fracture mouth.