Effect of fracture permeability and stress coupling on thermal extraction performance of CO 2 -EGS

Abstract During the extraction process of CO 2 -Enhanced Geothermal Systems, fluid flow and heat exchange not only alter the temperature and seepage fields of the rock mass but also induce rock deformation, which in turn affects the evolution of fracture permeability. Informed by geological data of mid-depth hot dry rocks from the Xujiaweizi area in the Songliao Basin, a three-dimensional discrete-fracture CO 2 -EGS model was developed to investigate the thermo-hydro-mechanical behavior of the system, explicitly accounting for the coupling between fracture permeability and stress. The evolution of the CO 2 -EGS stress field and fracture permeability is investigated, and the effects of fracture permeability and stress coupling on the system’s thermal recovery performance are analyzed. The results show that CO 2 injection induces thermal contraction of the rock mass, generating negative volumetric strain. This contraction promotes fracture opening, thereby enhancing fracture permeability, which exhibits an exponential growth trend. The increased permeability improves fluid transport capacity and heat exchange efficiency. Furthermore, the thermal-hydro-mechanical model that accounts for the coupling of fracture permeability and stress demonstrates superior thermal recovery performance.