Influence of Cross Mining Tunnel on Geothermal Resource Utilization in Abandoned Mines

The influence of cross mining tunnel on geothermal resource utilization in abandoned mines is that many mines are closed or abandoned, and the cross mining tunnel makes it possible to absorb and transfer geothermal energy resources over a wider area without hydraulic fracturing. In contrast, the mining tunnel closed during the operation phase due to ventilation, drainage design, or mining area requirements can be opened and merged into the main mining tunnel after the mine is abandoned to activate a larger area of high-temperature surrounding rocks. To explore the effect of interconnected cross-alley on geothermal resource utilization in abandoned mines, this paper establishes a numerical model to analyze the intersection angle and backwater parameters of connected alleyways, finds the gain effect of heat transfer under a slight angle, proposes the positive flow addition step (FPAS), and quantifies the misalignment symmetry phenomenon of each alleyway at the appropriate location. It is concluded that: (1) the interconnection of cross mining tunnels increases the inlet and outlet temperatures to 7.31–7.81 °C, an increase of 5.2–12.37% compared to the condition without cross mining tunnels; (2) the cross mining tunnels distributed in 0 ± 10°, 90 ± 50°, and 90° directions have a more significant gain effect on water temperature, and the positive flow addition step (FPAS) can quantify the gain effect of water temperature in the center. FPAS can quantify the temperature difference due to water flow direction on both sides of the centrally symmetric cross-alley; (3) when the number of cross-alley >1/150 m, the gain effect of increasing the number of cross-alley on temperature is no longer apparent, and the recharge flow rate of 750 m3/h is considered to be the cut-off value to produce the temperature difference change.