Fault zone mechanical response under co-exploitation of mine and geothermal energy: The combined effect of pore pressure and mining-induced stress

Abstract As the mine depth around the world increases, the temperature of the surrounding rock of the mining workface increases significantly. To control the heat hazards, the hot water in the mining floor is developed during mining to decrease the mining workface temperature while also developing geothermal energy. This method is called the co-exploitation of mine and geothermal energy (CMGE). The geothermal development may precipitate the large-scale failure of the nearby fault zone during the mining process. However, the evolution of shear slide and shear failure of fault under geothermal production/reinjection during mining is missing. Therefore, a fully-coupled hydraulic mechanism (HM) double-medium model for CMGE was developed based on the measured data of the Chensilou mine. A comparative analysis of the mechanical response of fault between CMGE and single mining was conducted. The disturbance of geothermal production pressure and reinjection pressure under mining on fault stability were respectively expounded. The results indicate that: (1) The disturbance of geothermal reinjection amplifies the disturbance of mining on fault stability. The amplified effect resulted in a normal stress drop of the fault, further leading to a substantial increase in shear slide distance, failure area, and cumulative seismic moment of fault compared with the single mining process. (2) As the distance of reinjection well to the fault decreases, the fault failure intensity increases. Setting the production well within the fault is advantageous for controlling fault stability under CMGE. (3) The essence of the combined disturbance of CMGE on the nearby fault is the overlay of tensile stress disturbance on the fault rock mass of the mining and geothermal reinjection. Though the geothermal reinjection causes a minor normal stress drop of fault, it can result in a more serious fault failure under CMGE. This paper supplies a significant gap in understanding the nearby faults failure under CMGE.