Utilizing underground mined-out space as geothermal reservoir for water storage: A study on temperature field evolution

Abstract:: The development of mine geothermal energy has become a key issue in the exploitation of deep green resources. To investigate heat extraction methods using water storage in deep underground spaces and the evolution of temperature fields, this study integrated laboratory experiments, numerical simulations, and theoretical analysis. The thermal conductivity of surrounding rocks in typical deep mines was measured, and a numerical model for heat extraction via water storage in underground spaces was developed and validated. The temperature field evolution under various influencing factors was examined, revealing the underlying heat transfer mechanisms. The results indicate that the thermal conductivity of coal, granite, shale, sandstone, and limestone increased by 17.8 %, 16.6 %, 10.4 %, 5.2 %, and 3.2 %, respectively, under saturated conditions. This suggests that saturated surrounding rocks exhibit enhanced thermal conductivity, thereby improving heat extraction efficiency. The maximum deviation between the numerical model and experimental curves was <1 °C, confirming the model’s reliability for simulating temperature field evolution. Heat transfer efficiency in the extraction space is proportional to the degree of rock fragmentation and the length of heat exchange channels, and inversely proportional to the inclination and width of the channels. Finally, a theoretical convection heat transfer model was established to elucidate the convective heat exchange mechanism between water and surrounding rocks. This model clarifies the evolution of the temperature field during water storage and heat extraction, providing a theoretical foundation for applying this technology in deep coal mine underground spaces.