Research status and progress of geothermal energy development and utilization from closed/abandoned coal mines

Exploring innovative ways to develop clean energy is a key driving force to achieving the “Double Carbon” goal in China.Low enthalpy geothermal resources(< 85 ℃)are a kind of net-carbon clean energy that can speed up the decarbonization process while meeting the thermal energy needs of residents.However, the mining of low-enthalpy geothermal energy faces a series of problems such as extremely high investment costs and serious environmental and geological disasters, which limit the large-scale development and utilization of geothermal resources.Due to the abundance of water, heat and space resources in closed/abandoned coal mines, it is possible to innovatively develop low enthalpy geothermal resources as well as extend the economic life of the mines to reduce their negative impact on the environment and economy.To realize this initiative, it is necessary to conduct a comprehensive overview of the technology, economy, environment, and policies related to the extraction of geothermal energy from abandoned mines.Therefore, an extensive literature review was conducted to overview the research results in terms of the system, heat source, demand and policy from the perspective of the principle of geothermal energy development, especially a detailed analysis of mine water volume, connectivity and temperature characteristics and its affecting factors.Furthermore, the research progress of assessing the feasibility of geothermal energy utilization in abandoned mines through analytical models, numerical simulations and field experimental methods were addressed.In addition, in order to illustrate the potential of geothermal energy extraction in abandoned mines, the dynamic recharge mechanism of surrounding rock was considered.Taking Zhangji mine in Xuzhou mining area as a case, the available geothermal resources were estimated.The results show that the static energy storage of Zhangji Mine is about 278 000 MW·h.The surrounding rock recharge heat(0.5 year)is about 4 731.4 MW·h.The carbon emission factor of the energy supplied by the system is only 0.05 kg/(kW·h).Compared with fossil energy, carbon emissions are reduced by about 13 000 t.Although the dynamic recharge heat is considered, the rate of mine geothermal supplement is still relatively slow.Therefore, future research should focus on the development of abandoned mine geothermal resources in a multi-energy complementary way by combining wind or solar energy to use abandoned mines as a key structure for thermal energy production-storage to improve the stability of the geothermal system.