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

Abstract

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.

Study on the influence law of well location and water injection displacement on heat extraction performance of EGS

“…The isolated and unconnected natural fractures in the formation also play a certain role in heat transfer and seepage, and these factors are not taken into account. The fluid flow‐heat transfer analysis model of vertical multifracture in EGS was proposed for the first time, and the results show that fracture aperture, initial fluid temperature, fluid density, and initial rock temperature have significant effects on instantaneous heat extraction efficiency 18 . This paper studies the influence of injected working fluid temperature on the heat recovery performance of EGS 19 .…”

“…The fluid flow-heat transfer analysis model of vertical multifracture in EGS was proposed for the first time, and the results show that fracture aperture, initial fluid temperature, fluid density, and initial rock temperature have significant effects on instantaneous heat extraction efficiency. 18 This paper studies the influence of injected working fluid temperature on the heat recovery performance of EGS. 19 However, the model adopted in this study does not include fractures and does not involve the coupling between multiple physical fields.…”