Abstract

Geothermal extraction in mine mainly utilizes Enhanced Geothermal System to recovery heat from deep thermal reservoirs. The extraction potential of stimulated thermal reservoirs strongly depends on the efficient exploitation of fractures. The research is aimed to establish a multi-fracture model for mine reservoirs to reveal the mechanical response and evolution of thermal recovery performance under thermal–hydraulic-mechanical coupling. The existence of blast fractures improves the connectivity of the conventional fracture network, which enhances the thermal recovery capacity of the reservoir. The permeability changes of the rock matrix and blast fractures are more obviously affected by the pressure, and the process is divided into two phases: a rapid change phase (the first 5 years) and a stabilization phase (5–30 years). The range of thermal stress and pore pressure on the reservoir is directly related to the distribution of multiple fractures, and the thermal stress is lower than the pore pressure, and the maximum of both occurs at the fracture top connected with injection well. During the thermal recovery, the effective stress near the production well is higher than that near the injection well, and the cumulative displacement is 1.9 cm. In 1.5–––4 km depth, the ratio of porous elasticity effect of rock matrix fluctuates around 21 %, thermoelastic effect ranges from 7.6 % to 16.3 %, while the in-situ stress effect is the dominant factor, accounting for 65.7 % to 67.6 %.