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Characteristics and Genesis of The Jixianion Geothermal Reservoir In The Xiong County of The Xiong'An New Area, China
Geothermal resources are extremely abundant within the Xiong County area of the Xiong'an New Area. The geothermal resources development and utilization of the famous Xiongxian model, owing to the in-depth study on the geothermal reservoir of the Neogene sandstone and karst in the upper part of Jixianion Wumishan formation, has been displayed in front of the world. With the large-scale construction of the Xiong'an new area, there will be a huge demand for geothermal resources within deep karst reservoir. Problems focusing on unclear understanding of the characteristics of deep Jixianion geothermal reservoir and inadequate research of the genetic mechanism about strong reservoir heterogeneity restrict the efficient exploration and sustainable development and utilization of deep geothermal resources in this area. Based on these latest obtained data of typical field outcrops, drilling, logging, seismic analysis and testing, a comprehensive geological and geophysical characterization on the karst geothermal reservoirs heterogeneity of Jixianion Gaoyuzhuang and Wumishan formations was carried out in the Xiong County area, Xiong'an new area. Also, the genesis about strong heterogeneity of deep karst reservoirs within the Jixian system was discussed by analyzing tectonic evolution and karstification. Research suggests that terms of geothermal reservoir properties, mainly composed of grain dolomite, algal dolomite, argillaceous dolomite, granular dolomite, siliceous dolomite, chert dolomite and karst breccia dolomite, are similar for Gaoyuzhuang and Wumishan formations. The Gaoyuzhuang Formation is of typical fissure-pore and pore types, relatively poorer in reservoir property with a porosity of 2%～6% and permeability of 0.001～1 mD. Whereas, the Wumishan Formation is dominated by the composite pore-cavity-fissure type, relatively better in physical property with a porosity of 4%～8% and permeability of 0.1～1 0mD. Geothermal well pumping test shows that the Wumishan formation has a larger water output capacity of 100～180m³/h than that of the Gaoyuzhuang Formation of 10～120m³/h. In conclusion, multiple factors of structural rupture, supergene dissolution, hydrothermal karst and geothermal water dissolution control the development of high quality karst reservoir in this area. Indosinian to Yanshanian tectonism caused the uplift and denudation of the pre-tertiary system, resulting in the strongly exposure, supergene dissolution and structural fracture of the Wumishan formation. Wumishan and Yangzhuang formations within part areas have been denuded, resulting in a strong transformation of Gaoyuzhuang Formation. This period is extremely important for the development of the Jixianion geothermal reservoir. Himalayan period was the development stage of fault depression to depression. These deep buried Jixianion geothermal reservoirs were further transformed by structural fracture, hydrothermal dissolution and geothermal water dissolution. These studies can provide theoretical and data support for the formation mechanism of deep karst geothermal reservoir and the efficient exploration, development and utilization of geothermal resources within the Xiong County of the Xiong'an New Area and even North China.