Geological characteristics and potential evaluation of medium-deep geothermal resources in Changsha Basin, Hunan Province

Hunan Province has relatively scarce primary energy resources. As an alternative energy source, geothermal energy is significant for optimizing the energy structure and promoting sustainable development. Historically, geothermal exploration in Hunan Province has primarily focused on uplifted mountain-type hydrothermal resources, with insufficient attention on hydrothermal resources in sedimentary basins. In recent years, Changsha Basin has demonstrated promising geothermal resource potential. However, its geological characteristics, formation mechanisms, and reserve scale remain inadequately understood. Based on previous research findings and drilling data, this study systematically analyzed key geological elements of the geothermal system in the Changsha Basin, including heat source, reservoir, caprock, and conduit. A geothermal genesis model was constructed. Furthermore, Monte Carlo simulation was used to conduct a quantitative evaluation of the geothermal resource potential. The results indicated that the primary heat source for the medium-deep geothermal resources in the Changsha Basin was mantle-derived conductive heat, resulting from mantle material uplift under an extensional tectonic regime. The geothermal reservoir mainly consisted of Upper Paleozoic carbonate rocks, with a relatively closed groundwater environment and prolonged water-rock interaction. The thickness of the caprock and the structural configuration of the basin interior influenced the geothermal field distribution. Regional faults and the development of pores and fractures provided good thermal conduction pathways. The average geothermal resource in the Changsha Basin was 9.85×108 GJ, equivalent to 0.34×108 t of standard coal, which could meet the heating demand for approximately 176.68×108 m2 of building area. Overall, the geothermal resources in this region are economically viable for development, with good social, economic, and environmental benefits. These findings can provide a reference for the exploration and development of medium-deep geothermal resources in the Changsha Basin, as well as for the evaluation of sedimentary basin-type geothermal resources in Hunan Province.