Abstract:
The North China Coalfield is an important coal base. It also contains abundant geothermal resources. It exhibits potential for the synergistic development of coal and geothermal resources. However, current geothermal studies in this area are mostly focused on shallow strata. These studies are relatively scattered. This hinders the overall evaluation and exploration of regional geothermal resources. The geothermal distribution characteristics are systematically analyzed. The influencing factors and genetic mechanisms are explored in depth. This analysis provides a scientific basis for the exploration of middle-deep geothermal resources. The results show that both terrestrial heat flow and geothermal gradient generally decrease from east to west. In the eastern Bohai Bay Basin, the average values are 69.0 mW/m
2 and 36.2 ℃/km, respectively. In the western Ordos Basin, they are 61.0 mW/m
2 and 29.8 ℃/km, respectively. This difference is mainly related to the lithospheric thickness (thinner in the east, thicker in the west). It is also related to the remote thermal effect of the Western Pacific Plate subduction. The geothermal distribution is mainly controlled by multiple factors. These factors include geological structure, lithology, groundwater activity, and heat source mechanisms. Fault structures are the dominant controlling factor. They significantly affect the spatial pattern of the geothermal field by regulating groundwater migration and accumulation. The genetic models mainly include three types. They are the buried-hill type in sedimentary basins, the geopressure type in fault-depression basins, and the deep-circulation type in uplifted mountainous areas. In the buried-hill type, the reservoir is characterized by a carbonate basement. Heat is mainly derived from deep mantle heat conduction due to lithospheric thinning. Heat is also derived from radiogenic heat of basement rocks. The heat is transferred through fault networks to porous-karst reservoirs. Finally, it is sealed by the overlying thick clay caprock. The geopressure type is formed in the deep parts of fault-depression basins. It features clastic rock reservoirs with large burial depth and high pressure. The high-temperature and high-pressure environment is created by restricted drainage during compaction. It is also created by closed thermal expansion. Under the sealing of thick caprock, it accumulates thermal energy and associated dissolved gas resources. The deep-circulation type mainly occurs in uplifted mountainous areas. Atmospheric precipitation circulates deeply along fault-fracture systems. It is heated during deep circulation. Driven by thermal buoyancy and topographic relief, it emerges as hot springs at the surface. Thus, it forms an open discharge system. The shortcomings of current geothermal research in the North China Coalfield are pointed out. Future research priorities are proposed. They include the occurrence regularity and genetic mechanisms of middle-deep geothermal resources. They also include the theory and key technologies for coal–geothermal synergistic development. In addition, they include the disturbance mechanism of coal mining/closure activities on the geothermal field.