A coupled thermal–hydrological–mechanical model for geothermal energy extraction in fractured reservoirs

Abstract

Understanding fluid flow in fractured porous media under coupled thermal–hydrological–mechanical (THM) conditions is a fundamental aspect of geothermal energy extraction. In this study, we developed a fully coupled THM model, incorporating porosity and permeability variations, to scrutinize the process of geothermal energy extraction within fractured porous reservoirs. Moreover, we accentuated the significance of natural fracture orientation and hydraulic fracture permeability on fluid trajectories and heat extraction efficiency. Simulation results revealed that hydraulic fractures predominantly govern fluid channels and thermal exchange between injected water and the reservoir. Interconnected natural fractures bolster water migration into the reservoir, while detached fractures exert minimal influence on fluid dynamics, underscoring the crucial role of fracture connectivity in optimizing heat extraction efficiency. The sensitivity analysis indicated that larger fracture angles marginally hinder pressure and cool-water dispersion into the fractured reservoir, resulting in subtle enhancements in heat extraction rates and average production temperatures. An upsurge in hydraulic fracture permeability augments fluid velocity and thermal exchange, thereby fostering heat extraction efficiency. The THM model developed in this study offers a comprehensive insight into fluid flow within fractured porous media and its implications on geothermal energy extraction.