Evaluation method of underground water storage space and thermal reservoir model in abandoned mine

A large number of mines are closed or abandoned every year in China. Geothermal utilization is one of the important ways to efficiently reuse underground resources in abandoned mines. How to calculate the volume and distribution of underground water storage space is the key to accurately evaluate the sustainable geothermal production in abandoned mines. In this paper, according to the multi-scale characteristics of the underground space in abandoned mine, the flow and heat transfer equations in the multi-scale space are sorted out systematically, and the calculation methods of different secondary space volumes are derived in detail. Taking Jiahe abandoned mine as the background, the volume and distribution of underground secondary space are calculated, and three heat storage evaluation models considering different water storage spaces are established by using COMSOL. The simulation results show that there are great differences among different models, and the results of the equivalent porous media model considering the multi-scale space are most consistent with the reality. Sensitivity analyses of key parameters model results indicated that the heat production is closely related to not only the recharge flow rate but also the recharge temperature and operating time. Furthermore, the energy saving and emission reduction benefits of geothermal utilization in abandoned mines are calculated, the results show that geothermal utilization of abandoned mines can effectively reduce energy consumption and CO₂ emissions, and it has great economic benefits.