A Gradient-Enhanced Thermo-Poro-Elastoplastic Finite-Element Model for Stimulated Volume Evolution in Porous Media

This paper is aimed at presenting a mixed finite-element model that is capable of dealing with nonlinear coupled thermo-poro-elastoplastic simulations of porous media. The model benefits from the generalized Biot theory for modeling of the fluid–solid interaction. The porous media is considered to be isotropic, and obeys the linear elastic hypothesis for its behavior before yielding. For after yielding, the behavior of the media is governed by the well-known Drucker–Prager criterion that is combined with the linear isotropic softening, and enhanced with gradient-based generalization. The latter generalization rectifies the strain localization issues that cause mesh-dependent results in the finite-element model. The specific solver for the finite-element model, which is capable of overcoming various kinds of numerical difficulties stemming from different types of couplings and nonlinearities, is equipped with a consistent tangent operator for maximizing the convergence rate in the solution procedure for obtaining inelastic deformations coupled with pore fluid pressure and temperature. Finally, some real-scale practical reservoir stimulation simulations are conducted and the capability of the model in simulation of the permeability/injectivity enhancement due to the stimulated dilation volume evolution is demonstrated.