Enhanced geothermal systems (EGS) is currently the most efficient method to mine heat from hot dry rock (HDR) reservoirs. The coupled thermo-hydro-mechanical (THM) effect therein is of critical importance to predict the long-term performance of EGS. A novel 3D THM coupling model integrating displacement discontinuity method (DDM), finite volume method (FVM) and finite element method (FEM) is developed in this study to aid such prediction. The present model is first validated against analytical solutions, and then applied to a penny shape EGS to simulate a 30-year prolonged injection. The simulation results reveal that EGS maintains high productivity during the early injection stage but once thermal drawdown takes place, the EGS productivity degrades rapidly. The fracture aperture model employed in the present study is capable of simulating hydraulic fractures in which the fluid pressure is large enough to overcome the normal stress exerted to the fracture faces and thus jack the fracture open. In contrast, most early studies adopted a compressive aperture model, where a substantial part of the normal stress is borne by fracture gouge/roughness. The strength of DDM + FVM + FEM scheme lies in the efficiency and versatility of simulating fractures. Our study indicates that the DDM + FVM + FEM scheme has high potential to serve as a competent alternative to performing the THM coupling simulation in EGS.

增强型地热系统（EGS）是目前从干热岩（HDR）储层中开采热量的最有效方法。其中耦合的热-水-机械（THM）效应对于预测EGS的长期性能至关重要。结合位移不连续法（DDM），有限体积法（FVM）和有限元法的新型3D THM耦合模型（FEM）是在这项研究中开发的，以帮助进行此类预测。本模型首先针对分析解决方案进行了验证，然后应用于便士形状的EGS以模拟30年的延长注射。仿真结果表明，EGS在注射初期就保持了较高的生产率，但是一旦发生热压降，EGS的生产率就会迅速下降。本研究中使用的裂缝孔径模型能够模拟水力裂缝其中的流体压力足够大，足以克服施加在裂缝面上的法向应力，从而顶断裂缝。相反，大多数早期研究采用压缩孔径模型，其中法向应力的很大一部分由裂缝/粗糙度承担。DDM + FVM + FEM方案的优势在于模拟裂缝的效率和多功能性。我们的研究表明，DDM + FVM + FEM方案具有很高的潜力，可以作为在EGS中执行THM耦合仿真的有效替代方案。