| As one of the most favorable areas for the development and utilization of Karst thermal reservoirs type geothermal resources in Central and eastern China,The middle-upper Proterozoic Carbonate rock karst thermal reservoirs in Xiongxian geothermal field have shallow burial depth,high water temperature,large water volume and easy recharge.Based on the data of drilling temperature measurement,rock thermal properties and heat flow,the shallow temperature field and heat flow distribution in the research area are portrayed.By using two-dimensional finite element numerical simulation method,two-dimensional temperature field simulation and lithospheric thermal structure research of two geoscience sections were carried out,and the influence of basement fluctuation,groundwater activity and magmatic activity on geothermal field was analyzed.the genetic model of Xiongxian geothermal field is formed.The following conclusions reached in this paper can be made:(1)According to the drilling temperature curve,The temperature of the upper sedimentary cover and the bottom metamorphic bedrock increases linearly with depth,and the heat transfer model is mainly heat conduction;the temperature of carbonate rock segment is homogeneous height and heat convection is the main transfer model.The geothermal gradient of rock cap in Xiongxian geothermal field is between 40 and75℃/km,the average value is 51℃/km,the distribution direction is mainly NE and NNE,which is consistent with the strike of the fault structure.The geothermal gradient in the uplift area is higher than that in the depression area.(2)Distribution of rock thermal conductivity and heat generation rate shows a sandwich structure.The average thermal conductivity of dolomite is the highest,5.46W/(m·K),and that of sandstone and bottom metamorphic bedrock are 2.15 W/(m·K)and3.13 W/(m·K)respectively.The average heat generation rate of dolomite is the lowest,0.5μW/m~3,sandstone and metamorphic bedrock are 0.98μW/m~3 and 0.79μW/m~3.The dolomite segment has high thermal conductivity,low heat generation,high porosity and high permeability.(3)The range of heat flow in Jizhong depression is between 33 and 106 m W/m~2,and the average heat flow is 58.5 m W/m~2,which is lower than that of Bohai Bay Basin,64.4m W/m~2.The range of heat flow in the research area is between 79.1 and 106 m W/m~2,and the average heat flow is 85 m W/m~2,the phenomenon of heat flow higher than upper limit of conductive heat flow of 83.72 m W/m~2,indicates that heat flow influcencing factors in research area is affected not only by conduction heat flow,but also by deep water upwelling along the fault zone to form convective heat flow,It is heat flux.The average heat flow values of Rongcheng uplift and Gaoyang uplift are 74.1 m W/m~2 and 61.9m W/m~2,and the surrounding depressions is low heat flow area,indicating that the heat flow value is affected by base fluctuation.(4)The Bohai Bay Basin is a typical"hot mantle cold crust"basin,The range of mantle heat flow is between 25 and 45 m W/m~2,the crust-mantle heat flow ratio is between0.52 and 0.8,and the thickness of thermal lithosphere gradually decreases from 95～115km in the western Jizhong depression to 80～90km in the eastern Jiyang depression,which is thicker than the western Taihang mountain uplift in and the northern Yanshan uplift.Within the Jizhong depression,the uplift areas have higher mantle heat flow value and lower crustal heat flow value than the depression,with the highest mantle heat flow is Niutuozhen uplift,approximately 36～39 m W/m~2,the crust-mantle heat flow ratio is between 0.6 and 0.75,the thickness of thermal lithosphere is between 93 and 105km,and the thickness of thermal lithosphere in the depression area is between 93 and 115km,which is slightly thicker than uplift area.(5)The present temperature field of Xiongxian geothermal field is the result of deep lithosphere thermal state control and shallow factors.In the deep,due to the subduction and subduction rate of the Pacific plate,the lithosphere experienced multi-period stretching and thinning,and mantle material upwelled,Mantle heat as the main heat source determined that the area had a high heat flow background.On the shallow surface,the thermal refraction effect caused by the higher thermal conductivity of the bedrock in the uplift area makes the heat flow value in the uplift area higher than that in the depression area,forming a dome-like thermal anomaly.The atmospheric precipitation,as the main source of recharge,migrated to the depth of the study area along the deep and large faults.The water-conducting faults such as Niudong fault,as the channel of groundwater migration,have the characteristics of longitudinal water-conducting and transverse water-blocking.The upwelling of underground hot water along the fault zone causes local thermal anomalies.Magmatic activities has no effect on the distribution of temperature due to its long time of activity. |
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