NUMERICAL SIMULATION ON THE HEAT EXTRACTION OF ENHANCED GEOTHERMAL SYSTEM WITH DIFFERENT FRACTURE NETWORKS BY THERMAL-HYDRAULIC-MECHANICAL MODEL

Hot dry rock (HDR), as a kind of geothermal energy resource, has attracted much attention due to its wide distribution and huge reserves. This paper presents a numerical study on energy mining in the HDR by the enhanced geothermal system (EGS). The thermal-hydraulic-mechanical coupling model is employed in these simulations. The multi-field evolution process and the influence of the fracture parameters on the heat recovery performance of an EGS are analyzed comprehensively. The results show that the fractures parallel to the connecting line of the injection-production well can lead to an early thermal breakthrough, resulting in a thermal recovery performance decrease, while fractures perpendicular to the connecting line between the production and injection wells can enhance the production temperature of an EGS, when compared with the reservoir without fractures. The production temperature drop rate of the EGS with percolated fracture network is much quicker than that of the EGS with an isolated fracture network. Additionally, short fractures can lessen the potential for working fluid preferred flow channels to emerge; therefore, an EGS with short fractures may operate better than an EGS with lengthy fractures.