Pore Pressure and Stress Distribution around the Wellbore in Shale Formation Based on Generalized Plane Strain Principles

Abstract

This article presents a new finite-element model for investigating the pore pressure and stress distribution around the wellbore in shale formations. In comparison with analytical and plane strain model, the proposed model is based on generalized plane strain principles and is suitable for any directional well in an anisotropic formation. Meanwhile, the model is more effective than the three-dimensional model. The FEM model takes thermal and chemical effects into consideration, so a nonlinear thermo-chemo-poroelastic coupling theory is used to analyze the problem. It is proved that the present model is validated by the existing analytical model. The effects of the thermal gradient, chemical potential, and elastic anisotropy on pore pressure and stress distribution are discussed. It is illustrated that lower temperature and chemical potential could prevent pore pressure and effective radial stress increase and reduce the risk of wellbore failure. The influence of the Poisson’s ratio anisotropy on pore pressure and effective stress is far smaller than that of the Young’s modulus.