A multiphysics method for long-term deformation analysis of reservoir rock considering thermal damage in deep geothermal engineering

Abstract

The deformation or failure behavior of reservoir rock in deep geothermal engineering has substantial influences on heat extraction efficiency. Accurate reservoir analyses must consider complex geological settings and factors, such as crustal stress, fluid pressure, high temperature, thermal damage, and long-term deformation/failure. The innovation of this work is that, by introducing a cooling damage model and the Norton-Bailey (NB) creep model into the Drucker-Prager - distinct lattice spring model (DP-DLSM), we developed a multiphysics numerical method (called NB-DP-DLSM) to achieve the long-term mechanical analysis of reservoir rock considering thermal damage in deep geothermal engineering. Through verification with experimental data, the proposed method was demonstrated reasonable. By developing a coupling linkage, the NB-DP-DLSM can be coupled with other numerical methods that are used to solve the temperature field of reservoir rock. After inputting the temperature field into the NB-DP-DLSM, a thermomechanical problem can be simulated by considering thermal expansion/shrinkage, thermal damage, and creep. Finally, we used the NB-DP-DLSM to simulate a single fractured geothermal model and a pipe geothermal model for 20 years. By doing so, accurate mechanical analyses can be derived, and some conclusions were obtained. Cooling damage is a nonnegligible factor in deep geothermal exploitation. It could enlarge the deformation of fracture and may accelerate the failure process during creep deformation. Fluid pressure is also an important factor. To better extract deep geothermal energy, maintaining a proper level of fluid pressure at different stages could control the deformation of fractures or wells. Simulation results revealed that the proposed method provides a potential tool to achieve accurate mechanical analyses of reservoir rock in deep geothermal engineering.