Accumulation patterns and exploitation and utilization targets of geothermal resources in the coal-bearing area in North China

Objective China is a major producer and consumer of coal resources in the world. The urgent need for the transition of the coal industry necessitates the investigation of both the origin and distribution patterns of geothermal resources in the coal-bearing areas of the country. The coal-bearing area in North China, with geothermal reserves accounting for 74.7% of the whole country, stands out as one of the areas with the most abundant geothermal resources nationally. This area encompasses four major coal-bearing basins: the Bohai Bay, Ordos, Qinshui, and Southern North China, with the lithospheric thermal state gradually weakening from east to west. Two types of geothermal reservoirs are found in the area, namely Cenozoic porous sandstone reservoirs and Cambrian-Ordovician karst-fissured carbonate reservoirs, with the latter proving preferred for the exploration, exploitation, and utilization of geothermal resources in coal fields due to its high temperatures, high water volume, and ease of reinjection.

Methods Based on the geothermal geological characteristics of coal fields in China, this study conducted a dynamic analysis of geothermal systems and, accordingly, selected the optimal targets for geothermal exploration and exploitation.

Results and Conclusions Four heat accumulation patterns are identified in the coal fields: (1) heat conduction by reservoir-cap rock assemblages consisting of carbonate reservoirs and coal seams as cap rocks. (2) heat conduction under the influence of bedrock surface undulations. (3) heat convection induced by groundwater motion in fault zones. (4) heat convection due to the weathered crust karstification of carbonate bedrock surfaces and the karstification of the contact surface of intrusions. The analysis of these heat accumulation patterns through numerical simulations of examples reveals that the optimal exploration and exploitation targets in the coal-bearing area in North China are identified as geothermal resources in deep carbonate reservoirs. Geothermal energy, featuring considerable reserves, cleanliness, and continuous supply as a type of non-carbon-based energy, will contribute significantly to the heat supply in the energy demands for electricity, fuel, and heat. The geothermal and coal resources in China overlap spatially, establishing the exploitation and utilization of geothermal resources as an effective way to the transition of the coal industry.