An analytical model for heat extraction through multi-link fractures of the enhanced geothermal system

Enhanced geothermal system (EGS) is the system for extracting the geothermal heat through the hydraulic fractured reservoir with the circulated fluid. Effective simulating method of the heat extract process is crucial to evaluate the efficiency of the EGS. In order to study the heat extraction process in the complex morphological fractures, the fluid flowing and heat transfer models through the analytical method in multi-link fracture are proposed. The Laplace transform method is applied to simplify the heat transfer equations for both fracture fluid and formation rock. The coordinates transformation is used to study the heat extraction performance in the EGS. The proposed analytical model is compared with the numerical model, which is verified to be efficient. The heat extraction performance of three multi-link fracture cases are simulated. The Case 2 with the longest fracture length has the highest production temperature. The parametric analysis shows that the longer flowing distance is helpful for producing higher fluid temperature and gaining more geothermal heat. The lower velocity and lower fracture width facilitate to obtain higher production temperature. While higher velocity and higher fracture width can extract more geothermal energy. From the above analysis, the multi-link fracture model with analytical method can be applied in EGS simulation.