Chemical Characteristics And Genetic Analysis Of Geothermal Water Of Qingshankou Formation In Daqing Area,Northern Songliao Basin

The Daqing area is located in the northern part of the central depression area of the Songliao Basin.Due to the influence of tectonic development and high geothermal field,the water outlet temperature of hot wells in the area is high,with a large inflow of water,and abundant geothermal water resources.However,the current level of research on geothermal water in the Daqing area is relatively shallow,and the mechanism of its formation is not yet in-depth enough.In addition,the long-term unreasonable development and utilization have caused environmental pollution and waste of geothermal water resources.Therefore,research will be conducted on the chemical characteristics of geothermal water in the study area to further reveal its genetic mechanism,thus providing a theoretical basis for the development and application of geothermal water resources in the Daqing area.This thesis takes the geothermal water of Qingshankou Formation in Daqing area,northern Songliao Basin,as the research object,and uses hydrogeology,structural geology,sedimentary geology and other disciplines as the theoretical guidance to sample and measure the parameters of geothermal water and underground cold water in the study area,and uses hydrogeochemistry and isotope analysis methods to analyze the chemical characteristics,isotope characteristics,supply mechanism,water rock reaction and cycle characteristics of geothermal water,Quantitatively estimate the thermal storage temperature of geothermal water using the Si O₂temperature scale,and calculate the mixing ratio of cold and hot water using the silicon enthalpy model.Through this study,the following insights have been gained:（1）The temperature of the geothermal water in the research area is 30.3-99.8℃,which belongs to the medium to low temperature geothermal water resource.The average p H value is greater than 7.75,and it is generally weakly alkaline.From the recharge area to the discharge area,the hydrochemical type changes from HCO₃·Cl-Na type to Cl·HCO₃-Na and Cl-Na types.The TDS content gradually increases,and the groundwater environment changes from open to semi open to semi closed.（2）The characteristics of hydrogen and oxygen isotopes indicate that the source of geothermal water supply in the study area is atmospheric precipitation,with supply elevations ranging from 1828.72 to 2460.67m,which is consistent with the elevation of the Great Xing’an Mountains in the northwest part of the Songliao Basin.Influenced by ancient climate water,geothermal water shows a mixture of atmospheric precipitation and sedimentary water in the strata.The results of ⁸⁷Sr/⁸⁶Sr values indicate the presence of geological fluids with low⁸⁷Sr/⁸⁶Sr values from deep sources,influenced by mantle derived mafic rocks.（3）By using the Na-K-Mg triangle diagram to determine that the geothermal water in the study area is in a local equilibrium water zone,the Si O₂solubility curve method and saturation index SI value judgment method were used to compare and analyze the equilibrium state of minerals in the geothermal water.A quartz thermometer was used to quantitatively estimate the thermal storage temperature of 51.45-101.69℃and the circulation depth of966.05-2332.69m.According to the silicon enthalpy equation method,the mixing ratio of cold water in this area is calculated to be 10%-60%.（4）The genetic model of geothermal water is that atmospheric precipitation infiltrates into the Greater Xing’an Mountains region to form groundwater,which is laterally replenished to the study area southward along the deep fault.During the long-term runoff process,it reacts with the surrounding rock to form a water rock reaction,and the hydrochemical types gradually become complex.Moreover,it is constantly heated by the heat generated by deep heat flow and radioactive elements.The Cretaceous thermal storage is overlaid with Paleogene and Neogene sandstones,mudstones,and Quaternary sediments as insulation cover layers,Ultimately,geothermal water resources will be formed.