Study on the Thermal-Hydraulic Coupling Model for the Enhanced Geothermal Systems

Enhanced geothermal systems (EGS) are the major way of the hot dry rock (HDR) exploitation. At present, the finite element method (FEM) is often used to simulate the thermal energy extraction process of the EGS. Satisfactory results can be obtained by this method to a certain extent. However, when many discrete fractures exist in the computational domain, a large number of unstructured grids must be used, which seriously affects the computational efficiency. To solve this challenge, based on the embedded discrete fracture model (EDFM), two sets of seepage and energy conservation equations are respectively used to describe the flow and heat transfer processes of the matrix and the fracture media. The main advantages of the proposed model are that the structured grids can be used to mesh the matrix, and there is no need to refine the mesh near the fracture. Compared with commercial software, COMSOL Multiphysics, the accuracy of the proposed model is verified. Subsequently, a specific example of geothermal exploitation is designed, and the spatialtemporal evolutions of pressure and temperature fields are analyzed.