Abstract:
This paper is the result of geothermal geological survey engineering.
Objective Dry hot rock resources have advantages such as clean environmental protection, abundant reserves, and good stability. The scientific development and utilization of dry hot rock can help achieve China's dual carbon strategy goals. The Guanzhong Basin in Shaanxi Province is a typical low-temperature geothermal field, and Huayin–Huazhou area has good geothermal geological conditions, making it a potential favorable area for dry hot rock exploration.
Methods On the basis of collecting and organizing geothermal geological data in the study area, through geothermal geological survey, geophysical exploration, sample collection test and numerical calculation, the distribution range of hot dry rock and the structural characteristics of reservoir and cap rock in the study area are basically identified. The thermal structure characteristics and heat source mechanism of lithosphere are analyzed. The formation mechanism of heat flow pattern is studied and the resource potential is evaluated.
Results (1) The type of dry hot rock resources in the study area is a typical sedimentary basin type, and the heat mainly comes from the higher mantle heat flow caused by the upwelling of the mantle diapir and the thinning and stretching of the lithosphere, followed by the decay heat of radioactive elements in crustal rocks. Under the background of high heat flow caused by Moho uplift and significant thinning of the lithosphere, the thermal conductivity of shallow strata is laterally uneven. The thermal conductivity of Taihua Group granite in Archean is high, while the thermal conductivity of the Cenozoic sandstone, gravel bearing sandstone, and mudstone is low, causing redistribution of heat flow. The reconvergence in the basement uplift area is the main heating mechanism of dry hot rocks in the area. (2) The geothermal gradient in the study area is 22.2–36.5℃/km, with an average of (33.0±2.0)℃/km. The geothermal heat flow is 53.7–89.2 mW/m2, with an average of (80.3±4.9) mW/m2. The geothermal gradient and geothermal heat flow show a trend of high low high low from west to east. (3) The heat flux at the bottom boundary of the sedimentary layer is 45.5–86.8 mW/m2, with an average value of (75.5±5.3) mW/m2; The heat flux at the bottom boundary of the upper crust is 29.2–62.5 mW/m2, with an average value of (54.5±4.8) mW/m2; The heat flux at the bottom of the middle crust is 17.1–50.0 mW/m2, with an average value of (42.2±4.9) mW/m2; The heat flux at the bottom of the lower crust is 15.3–48.1 mW/m2, with an average value of (40.4±4.9) mW/m2. (4) The heat flux ratio between the crust and mantle in the study area is 0.85–2.52, and the heat flux ratio between the middle crust and mantle is less than 1, accounting for 67% of the area. The Moho surface temperature ranges from 496.8 to 845.9 ℃, with an average temperature of (768.6±52.5) ℃. The Moho surface temperature is highest in the northwest and central corners, and lowest in the northeast corner. (5) Calculated the geothermal resources of hot dry rocks (≥ 150 ℃) within a depth range of 8 km in the study area. When the temperature of the deep formation is 150 ℃, the corresponding depth of the formation is 3.5–6.3 km, and the temperature at a depth of 8 km is 182.7–260.6 ℃. The total reserve of geothermal resources in dry hot rock is 46.1 EJ, equivalent to 2626.31 million tons of standard coal. Calculated based on a recovery rate of 2%, the exploitable resource reserve is 0.92 EJ, equivalent to 52.53 million tons of standard coal.
Conclusions This paper analyzes the heat source mechanism and resource potential of dry hot rocks in the Huayin–Huazhou area, providing a theoretical basis for the scientific utilization of dry hot rock resources and the sustainable evaluation of heat source supply in the future.
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