3D geological modeling of mine karst geothermal reservoir and geothermal resources evaluation

The traditional geothermal reservoir volume method is suitable for the evaluation of geothermal resources in large-scale regions, but there is a significant error when it is used for the evaluation of mine geothermal resources. On the basis of analyzing the characteristics of the geothermal system of the Cambrian karst geothermal reservoir, i.e., heat sources, fluid channels, reservoirs, caprocks and the heat fluid in the Pingdingshan mining area, a conceptual model of geothermal genesis in the Pingdingshan coalfield was established. Based on the geothermal geological conditions and drilling data ground and underground in No.10 Coal Mine of Pingdingshan Tianan Coal Mining Co., LTD., a three-dimensional geological model of the strata in the study area was established using Groundwater Modeling System software. The distribution of Cambrian karst strata and its overburden strata was displayed, and the Cambrian karst strata space was gridded and digitized. The integrated geothermal reservoir volume method for evaluating geothermal resources in mines was proposed and used to estimate the static resource quantity of the Cambrian karst geothermal reservoir in the study area, and the dynamic resource quantity of the geothermal reservoir was also evaluated. The relationship curve between the geothermal reservoir resource quantity and water level elevation was obtained. A complete water quality analysis was conducted on the karst geothermal water in the study area, and the corrosiveness and scaling properties of the geothermal water were evaluated. The results show that the Cambrian carbonate strata in the study area are the karst geothermal reservoir, and the heat mainly comes from high-temperature rock mass deep in the Cambrian Zhushadong Formation; surface atmospheric precipitation enters the deep rock mass through Cambrian limestone outcrops and deep faults around the mining area, and is heated along the way and stored in Cambrian limestone, after which the water continue to receive the heat from deep bedrock and then forms a hydrothermal karst geothermal reservoir; the static hot water resource of Cambrian karst strata in the study area is 7.68 billion m³, containing heat of 1.19×10¹⁸ J; the heat contained in the rock is 3.25×10¹⁸ J, with a total geothermal resource of 4.44×10¹⁸ J; the recoverable geothermal resources are 6.66×10¹⁷ J, equivalent to 22.7 million tons of standard coal; the Cambrian karst hot water has slight corrosiveness, with a slight to moderate degree of scaling. Corrosion and scale prevention treatments are required for metal pipelines and containers of the geothermal water.