Geothermal energy exploitation and storage in coal field under the dual carbon goal

The development of geothermal energy in coalfield can not only improve the temperature environment of coal mining, but also turn waste into treasure through the clean utilization of geothermal energy. Especially, it is of great prospect to store energy in the mined-out area of coalfield under the “dual carbon” goal at present. Herein, in this paper, it was estimated that the geothermal reserves in the main coal-bearing areas of China were 1.12 × 10¹⁹ kJ, equivalent to 379.539 billion tons of standard coal, and the recoverable geothermal reserves were 1.71 × 10¹⁸ kJ, equivalent to 56.931 billion tons of standard coal. Among them, the recoverable geothermal reserves of the coal-bearing area in North China account for about 74.7%, especially in the western area (Jin‒Shaan‒Meng‒Ning sub-region), where seven coal bases were distributed, including Shendong, Jinbei, Jindong, Jinzhong, Shaanbei, Huanglong (Huating) and Ningdong, with the richest coal resources, accounting for nearly 48.7%. It was further pointed out that the “synergetic mining of coal and geothermal energy” would be the main form of geothermal development and utilization in coalfield areas, which included three methods of heat extraction, such as pipe filling and burying, mine water in coal mine goaf and deep coal mine aquifers. In addition, it was proposed to utilize the coal mine goaf and the space freed up after drainage as the “geothermal reservoirs”, which should be taken as the direction of working in the next step. Besides, a detailed review was presented regarding the heat storage with backfill (phase-change) material, pumped storage with abandoned coalfield and energy storage with compressed air in the abandoned coalfield. Last but not least, a brief introduction was presented for the thermal disaster prevention and control technology of coal mine. In conclusion, the scaled coalfield energy storage, thermal disaster prevention and control, and geothermal utilization will be the main directions of coalfield geothermal research, development and utilization. Which is also an important channel to achieve the green transformation of coal mines and the national "dual carbon" goal.