Main Controlling Factors And Favorable Zone Prediction Of Xiongxian Carbonate Geothermal Field In Jizhong Depression

The buried depth of the Wumishan Formation is shallow which has excellent reservoir conditions in Xiongxian geothermal field,this area is the focus of geothermal development and utilization in Xiong'an New District.Through the field observation in the early stage combined with observation,thin section authentication,logging and other data,the main controlling factors of Xiongxian geothermal field are systematically analyzed,and the genetic model of this area is proposed.The evaluation criteria of carbonate reservoirs in this area are established and the favorable areas are predicted.The study found that the heat source in this area is mainly deep crustal conduction heat and radiant heat.The average geothermal gradient of the cap rock is 4.54°C/m,and the average geothermal gradient of the Wumishan Formation is 0.87°C/m.The water source is mainly from modern atmospheric and paleo-atmospheric precipitation from the Taihang and Yanshan Mountains at an altitude of over 500 m.The underground hot water circulates at the depth of 3500 m and flows along Baoding-Xushui fault,Rongcheng fault,Niudong fault and fractured karst system in this area.It is concluded that there may be a fault near the Niudong fault,by which water can moves up to the inside of the uplift.The reservoir and cap rock combination composed of dolomite reservoirs of the Wumishan Formation and the Tertiary and Quaternary sand-shale formations.Combined with the analysis of rock physical property data,based on the previous data,the porosity and permeability models of the Wumishan Formation reservoir in the study area are established,which has a good fitting effect.At the same time,the carbonate rock reservoir types of the Wumishan Formation in the study area are studied,and establish the logging identification standards for different types of reservoirs.The reservoirs of the Wumishan Formation in the Xiongxian geothermal field are further divided into four types,including fracture reservoir,porosity reservoir,fractured-porosity reservoir and cave reservoir.And the decision tree method is used to systematically identify the carbonate reservoirs of the Wumishan Formation to improve the reservoir prediction efficiency.The fractured reservoirs in the study area are mainly developed in vertical vadose zones,the porosity reservoirs are mainly developed in the horizontal phreatic zones and the transitional zones,the fractured-porosity reservoirs are mainly developed in vertical vadose zones and horizontal phreatic zones,and the cave reservoirs are mainly developed in the horizontal phreatic zones.The cop rock has good insulation effect,and the reservoir and cap rock combination is excellent.This paper comprehensively explores the formation key factors of Xiongxian geothermal area from four perspectives of “source,migration channel,reservoir and cap rock”,It is found that migration channels and reservoir development play an important role in the formation of carbonate geothermal fields,and proposes the genetic model of this area,realizes the forecast of favorable area of Xiongxian geothermal field which provides reference for the development and utilization of geothermal field in Xiongxian area.