Numerical simulation on unconventional mining of geothermal water in coal-heat co-mining mode

It is strategically significant for the mine in operation to investigate the development and utilization of geothermal water resources for realizing coal-thermal co-mining in the context of “carbon peaking and carbon neutral” in China. However, currently the coal-thermal co-mining technology is immature, and a further research is needed for the geothermal water extraction in operating mines. Thus, this paper presented an unconventional method for the underground mining of geothermal water based on coal-thermal co-mining theory and technical framework. In the studied mine area, the formation mechanism of thermal reserves was analyzed, the amount of geothermal water resources was estimated by the thermal reserve volume method, and the potential of geothermal water development was evaluated. Simultaneously, the thermal reservoir temperature field and production well water temperature variation were numerically simulated under the unconventional mining mode of geothermal water. The effects of production well-group parameters on the thermal reservoir temperature field and production well water temperature were analyzed and compared with the conventional method of geothermal water production. Finally, the social and economic benefits generated by the mine geothermal water mining and utilization were discussed. The results show that:(1) The static recoverable reserves of geothermal water in the mine is 1.14×10¹⁷ J,equivalent to 3.9 Mt of standard coal. The dynamic recoverable reserves is 2.95×10¹⁶ J/a, equivalent to 1.01 Mt/a of standard coal.(2) The water temperature of the production well is influenced by the temperature of the recharge water, with less relation to the recharge method. Meanwhile, it is affected by the temperature of the recharge water on the production well water temperature mainly in the late production period.(3) The thermal breakthrough time of the production well-group is advanced and the cooling rate is increased after the thermal breakthrough point with increasing production rate.(4) Balanced production has a beneficial effect on the life of producing wells.(5) Adjusting the production strategy of the unconventional mining mode can realize the coordinated mining of the production well-group and extend the life of the production well-group, resulting in a smaller average cooling rate than the conventional mining mode of the production wells.(6) Once the mine geothermal development system has been completed, the heating area of 170 000 m² in the coal mine and the bathing of all mine employees can be realized, reducing coal burning by 10 327 t and CO₂ emission by 26 900 t per year, creating economic benefits of 6.938 million RMB for the enterprise. Therefore, it is feasible to implement unconventional mining of underground geothermal water for hydrothermal high-temperature mines. And the efficient mining of geothermal water in mines can be realized by reasonably arranging the distribution of production well-group and scientifically formulating the production strategy.