Different Distribution of Deep and Shallow Geothermal Resources in Jizhong Depression under Complex Heat Transfer

The Jizhong Depression, Bohai Bay Basin, has enormous potential for geothermal resource development, but currently only the genesis mechanism of shallow to mid-temperature geothermal resources has been extensively researched, and the genesis mechanism of deep and high-temperature geothermal resources remains unclear. Based on regional geology, geothermal geology, and rock thermal properties, in this study it analyzed the characteristics and controlling factors of the deep temperature field in the study area and explored the deep and high-temperature heat accumulation mechanism under complex heat transfer processes of conduction and convection. The temperature gradient and heatflow in Jizhong Depression of the Bohai Bay Basin are relatively high, with a temperature gradient ranging from 27.4 ℃/km to 39.7 ℃/km, with an average of about 34.8℃/km, and a heatflow ranging from 50 mW/m² to 70 mW/m². The temperature field is affected by rock thermal conductivity, basement structures, and groundwater flow, and has complex differences in both plane and vertical distribution. Based on measured data, it was found that the shallow temperature is high but the deep temperature is low in the convex areas, and the shallow temperature is low but the deep temperature is high in the depressed areas, leading to the deep and high-temperature geothermal resources largely concentrated in the depressions within 5 000 m depth in Jizhong Depression, with the reservoir temperature reaching 190 ℃, and which can serve as potential favorable targets for exploring hot dry rock resources. The characteristics of hydrothermal geothermal resources in the uplift area and deep potential hot dry rock geothermal resources in the Jizhong Depression are studied from the perspectives of geological structure, source, storage, cap, and fluid, and a model of the accumulation of shallow hydrothermal geothermal resources and deep potential hot dry rock geothermal resources in the studied area was established. This study deepened our understanding of the genesis mechanisms and distribution patterns of deep and high-temperature geothermal resources in Jizhong Depression and even the Bohai Bay Basin, and has significant reference value for the exploration and utilization of hot dry rock geothermal resources.