Chemical Characteristics And Genetic Analysis Of Geothermal Water In Carbonate Reservoir In The Northern Jizhong Depression

In recent years,the Beijing-Tianjin-Hebei region has become a region with a high level of energy-related structural contradictions and serious air pollution,while the Beijing-Tianjin-Hebei hinterland is rich in geothermal resources in the Jizhong Depression.The development of geothermal energy can effectively optimise the energy structure of the Beijing-Tianjin-Hebei region and alleviate the pollution problem.Therefore,the research and analysis of geothermal water from carbonate rock thermal storage in the Jizhong Depression will provide a theoretical basis for the further development of geothermal resources.This paper takes the carbonate rock thermal storage geothermal water in the northern Jizhong Depression as the research object.On the basis of a brief analysis of the geothermal geological conditions in the study area,the hydrochemical characteristics,isotopic characteristics,thermal reservoir temperature characteristics and regional thermal characteristics of the study area are analyzed and researched,and the following understandings and conclusions are mainly obtained:（1）The hydrochemical types of the study area are clearly grouped.The hydrochemical types of the recharge area in the Taihang Mountains are HCO₃-Mg·Ca and its subtypes.The hydrochemical types of the runoff areas in the Beijing depression and Langfang depression tend to be complex,with a total of 7 types including HCO₃·SO₄-Na·Ca,HCO₃·SO₄-Na·Ca·Mg,etc.The chemical types of water in the excretion area of Niutuozhen uplift and Bazhou depression are Cl-Na and Cl·HCO₃-Na.From the recharge area to the runoff to the discharge area,the chemical types of water changed from simple to complex and tended to be simple,and the TDS content gradually increased.（2）The geothermal water in the study area is of the atmospheric precipitation genesis type,and its recharge elevation is about 585.7～1361.8m,which is consistent with the elevation of the Taihang Mountains in the northwest and Yanshan Mountains in the north,but the general pattern of 14C age change of geothermal water is gradually increasing from the northwest to the southeast,so the geothermal water in the study area mainly comes from the recharge of the Taihang Mountains in the northwest.（3）In this paper,various methods were used to estimate the thermal reservoir temperature.Combining the water-rock equilibrium analysis and the actual situation,it is concluded that the Na-K and Na-K-Ca geothermometer are not applicable to the thermal reservoir temperature estimation in the study area,and the average value of the quartz and chalcedony geothermometer estimation is more suitable as the thermal reservoir temperature,which is similar to the K-Mg geothermometer and the multi-mineral equilibrium method.（4）The geothermal reservoir temperature in the study area ranges from 46.2 to107.4℃,with the highest geothermal water temperature in the Niutuozhen uplift and the lowest geothermal water temperature in the Taihang Mountain area.And there are different degrees of cold water mixing in the geothermal water in the study area,the proportion of cold water mixing is 41%～87%,and the depth range of geothermal water circulation is 1639.1～3338.4m.（5）The study area is a"hot mantle and cold crust"type thermal structure,the heat source is mainly deep mantle heat flow,supplemented by rock radiogenic heat,the warming of geothermal water is mainly by heat conduction,supplemented by thermal convection.（6）The geothermal genetic model in the study area is that after the precipitation infiltrated into the groundwater in the Taihang Mountains,the groundwater is laterally recharged along the fault to the southeast.Under the long-term runoff,the groundwater undergoes a water-rock reaction,and the hydrochemical type gradually changes,and is continuously increased by the deep heat flow.When the temperature is high,convection is formed locally,and the overlying Tertiary sandstone and Quaternary sediments form a good thermal insulation cover,which is not easy to lose heat,and finally forms a good geothermal resource.