Distribution Characteristics and Genetic Mechanism of Geothermal Reservoirs in Wucheng Salient Geothermal Field

Driven by the "Xiongxian model" and environmental pressure, Hebei Province has become the largest geothermal heating urban agglomeration in China. Therefore, the study of geothermal and geological characteristics of Wucheng Salient has important guiding significance for geothermal development in Gucheng County, Hebei Province. In this paper, we studied the distribution of different types of geothermal reservoirs, physical properties of reservoirs, characteristics of geothermal water recharge and circulation path, and evaluation of geothermal resources by combining the logging, seismic and regional geological data including the analysis of hydrochemical characteristics and isotopic results. The results show that the geothermal field has two geothermal reservoirs: sandstone reservoir and karst reservoir. The former is widely stable and distributed, with the main aquifer as the lower Guantao Formation between 1200-1600 m deep. The geothermal water temperature ranges from 52-54°C, and average water yield between 75-123m/h. The favorable zones of karst geothermal reservoir are mainly in the anticlinal core of the Cambrian-Triassic extending in a north-south zonal direction with main aquifer as the upper Majiagou Formation, the lower Majiagou Formation and Liangjiashan Formation bewtween 2100-2900 m deep. The geothermal water temperature rangefrom 82-85°C, and the average water yield of of between 75-98 m/h. The geothermal water originates from recharge area of Taihang mountains in the west and Yanshan mountains in the north, moving horizontally along the NE-SW fracture zone and the karst unconformity to enter the shallow geothermal reservoir. It mixes in Wucheng Salient to form medium-low temperature geothermal water through Cangxian Uplift and Xingheng Uplift to form NaCl waters . The dating results of C indicate that the geothermal water of sandstone reservoir and karst reservoir is 21ka and 32ka. The Minghuazhen Formation and the Carboniferous-Permian strata are cap rocks of the two geothermal reservoirs, respectively. Based on detailed geothermal resource evaluation It is estimated that the total geothermal capacity amount to 4.86×10 GJ, equivalent to 16.6×10 of standard coal. The annual exploitation of geothermal resources can meet the indoor heating area of 110 million square meters with huge potential for further development.