Elastoplastic Analytical Investigation of Mechanical Response of Wellbore in Methane Hydrate-bearing Sediments

Abstract:

When drilling in methane hydrate-bearing sediments， the variation of temperature and seepage pressure around the wellbore likely leads to the hydrate dissociation， reducing the safety of wellbore. The analytical solution for wellbore mechanical analysis is derived accounting for the ideal elastic-plastic behavior of the formation， the Mohr-Coulomb yield criterion and non-associated flow rule. Based on a steady-state axisymmetric plane strain model considering the effect of hydrate dissociation on temperature， seepage flow and mechanical property， the stress and displacement solutions are presented under unbalanced and overbalanced drilling conditions. The analytical solutions agree well with the results by numerical methods under the same assumptions， as well as the complex conditions. The results show that the increase of the size of dissociated region leads to the expanding of plastic zone obviously within a certain range. The size of plastic zone is decreased with the reduction of Young's modulus of dissociated region under unbalanced drilling condition， while the result is inverse under overbalanced drilling condition.