Karst geothermal reservoirs are one of the two main types of reservoirs used for clean heating in northern China. There are 1,000 productive karst geothermal wells in the North China Plain (including Beijing, Tianjin city, and Hebei, Shandong, and Henan provinces), supporting the heating of about 100 million square meters of domestic space. However, the mechanism of hot water enrichment and heat accumulation is not clear. In this study, based on the geo-temperature logging, geothermal well yield measurements, isotopes, and hydro-geochemical data, the origin of the geothermal water, the evolution from a groundwater flow system to a geothermal water system, and its migration and enrichment mechanisms were investigated. The geothermal water is mainly concentrated in the areas containing both interbedded karstification and water-conducting faults and in the contact zones between intrusive and soluble rocks. The composite position of the four heat sources has the densest heat flow and the highest geothermal gradient, and thus, it is the heat flow accumulation area. The first source is the thermal accumulation of blanket shaped terrestrial heat flow conduction, the second source is the thermal accumulation of the high thermal conductivity diffluence in the uplift area, the third source is the belt shaped convective thermal accumulation in the deep fault zone and the contact zone between the intrusive and soluble rocks, and the fourth source is the conductive and convective thermal accumulation through the deep groundwater circulation. Under the heating of four heat sources, the cold springs evolved into hot springs. Based on the mechanisms of the heat accumulation and water enrichment, the prospecting model highlighting how to identify geothermal water enrichment and heat flow accumulation areas was developed.
