Detection of carbonate geothermal reservoir in Niudong fault zone of Xiong'an New Area and its geothermal exploration significance

In Xiong'an New Area,because of prohibiting the exploitation of sandstone geothermal reservoir,it is of a great significance to find out the distribution position and the resources quality of the karst geothermal reservoir of the Niudong fault zone,as an eastern boundary of the karst geothermal resources,for the compilation of geothermal resources development and utilization planning and the layout of overall energy utilization. Based on the detection data of the D09 borehole,as the first exploration well for karst geothermal reservoir in the high-speed railway area of the Xiong'an New Area,and combined with the interpretation results of seismic sections,the spatial distribution characteristics,physical properties of reservoir and single well productivity parameters of the karst geothermal reservoir in the Niudong fault zone are analyzed,and its guiding significance for geothermal exploration is also summarized. The results show that the karst geothermal reservoir in the Niudong fault zone is mainly siliceous dolomite in the Wumishan Formation of the Jixian System,which is distributed at the top of the broad,gentle anticline of the bedrock on the west side of the fault,and is high quality geothermal heating utilization resource with the stable layers thickness of about 2000 m,the roof buried depth of 1000~1200 m,the geothermal water temperature of about 70℃ and the single well production of about 102 m³/h. There are 122 fractured karst zones in the strata of 678 m from the top of the weathering crust in the D09 borehole,with the total thickness of 251.20 m,the fracture ratio of 37%,and an average porosity of 9.26%. The fracture rate and average porosity are obviously 50% higher than those of the geothermal wells out of the fault zone. A comparative analysis of geothermal gradient of the strata,geochemical characteristics of geothermal water and water-conductivity of reservoir between the D09 hole and the geothermal wells around the Niudong fault zone shows that the Niudong fault zone with a vertical fault distance of 7000 m is a deep fault of water-conducting and thermal-conducting in the basin. The fault zone defines the eastern boundary of the karst water-bearing systems in the Xiong'an New Area,constitutes a water channel for the Niutuozhen uplift and a oil-gas migration barrier for Baxian depression,and results in formatting a complete geothermal field of the Niutuozhen uplift with an area of 1000 km².