Genesis Of Geothermal Field And Evaluation Of Cenozoic Heat Storage Resources In Jizhong Depression

Jizhong depression is rich in geothermal resources,but only some areas have been developed and utilized on a large scale.There are still controversies about the formation mechanism of geothermal fields,and the exploration degree of Cenozoic thermal reservoirs is low.Based on geothermal geology,combined with the basic theories of structural geology,hydrogeology and sedimentology,this paper studies the characteristics of geothermal field in Jizhong depression by analyzing the collected data of hydrochemistry,well logging and seismic profile,and by using the methods of heat conduction simulation and groundwater chemical composition comparison,and analyzes the controlling factors of geothermal anomaly in the study area,According to the"heat storage volume method",the amount of geothermal resources of Cenozoic heat storage in Jizhong depression is calculated.The results show that the average geothermal heat flow in Jizhong depression is 64.4mw/m²,and the average geothermal gradient is 33.4?/km,which belongs to geothermal anomaly area.The vertical geothermal gradient has the characteristics of segmentation.The heat transfer mode of shallow strata is dominated by heat conduction,and the heat transfer mode of deep carbonate reservoir is dominated by heat convection;The thickness of the regional thermal lithosphere is relatively thin,which is mainly caused by the large-scale regional tectonic movement since Mesozoic.The thermal structure of the crust is of the hot mantle cold shell type;The shallow geothermal field is mainly controlled by basement undulation,and the influence of intrusive rocks on the present geothermal field can be ignored.The quality of sedimentary cover plays an important role in the formation and development of geothermal anomalies and deep dry hot rocks;In the study area,the source of heat storage water mainly comes from the precipitation in the northern Yanshan and Western Taihang Mountains.The hydrodynamic connection between surface water and heat storage water is weak.Gaoyang geothermal field and niutuozhen Rongcheng geothermal field belong to different geothermal systems;The cause of geothermal anomaly in Jizhong depression:the tectonic activity since Mesozoic has led to the lithosphere thinning in Jizhong depression,but the thick caprock has been deposited since Paleogene,which has played a good role in heat preservation,making the region present a high geothermal flow background,and the concave convex tectonic pattern makes the heat flow to the convex area to gather,resulting in geothermal anomaly in the tectonic unit,In some areas,due to the development of faults,the geothermal water is upwelling and the local geothermal anomaly is high;Combined with the regional geological profile,the conceptual model of geothermal field in Jizhong depression is summarized as follows:mantle source and crust source heat supply medium low temperature convection and heat conduction superposition concave convex heat accumulation meteoric water supply karst and pore type heat storage;According to the calculation results,the total amount of geothermal resources contained in Guantao Formation and Minghuazhen Formation in Jizhong depression is 1037.66×10¹⁸J,equivalent to 35.41×10⁸ tons of standard coal.Based on 100 years of exploitation and 25%recharge rate of sandstone,the annual heat supply area of recoverable resources can reach 3.13×10⁸m².In the southern Raoyang depression,Gaoyang uplift and Lixian slope,there are abundant Cenozoic heat storage resources with great development potential.This study will provide important scientific basis for geothermal development in the future.