Modeling study of the thermal-hydraulic-mechanical coupling process for EGS based on the framework of EDFM and XFEM

Simulation of thermal hydraulic-mechanical (THM) coupling process plays an important role in exploiting the hot dry rock (HDR) resources by enhanced geothermal systems (EGS). At present, the simulations are mostly performed by using the traditional finite element method (FEM) with very dense grids. Because of the considerable size differences between the fractures and EGS, a large number of unstructured grids should be adopted, leading to a significant computational burden. To address this challenge, the embedded discrete fracture model (EDFM) and the extended finite element method (XFEM) are combined in this paper. By doing this, the grid number can be dramatically reduced, which improves the computational efficiency while maintaining relatively high accuracy. The proposed model is verified by comparing it with two typical analytic solutions and COMSOL. Moreover, the new model is applied to analyze the pressure, temperature and displacement evolutions in a hypothetical EGS. The influences of some key variables on thermal extraction performance are also investigated.