Genetic Model Analysis Of Paleogene Geothermal System In Yitong Basin

In the 21st century,the demand of human beings for energy is increasing day by day.Geothermal energy as a new type of energy is gradually coming to people's vision.Yitong Basin is a typical medium-low temperature geothermal system with abundant geothermal resources.The surface temperature of geothermal water is mostly between 45?and 70?.Its geographical location is located in Jilin Province in the east of China,and it is structurally located in the north of Tanlu fault.Its formation is mainly controlled by the subduction of the Pacific plate to the Eurasian plate,which belongs to a typical Cenozoic rift basin.The reservoir-cap's relationship in the basin is good,the deep fault is developed,and the geothermal gradient is high,which provides favorable geological conditions for the formation of geothermal resources.In the existing research,the geothermal forming conditions of several hot springs in the basin have been analyzed,but the complete geothermal genetic model has not been established.Therefore,on the basis of previous studies,based on the stratigraphic characteristics,combined with fluid geochemical analysis,this paper analyzes the formation conditions of Paleogene Geothermal in the basin and establishes the genetic model.On the basis of previous studies on the geothermal system in the study area,this paper samples several geothermal wells in the study area and measures the ion component,gas composition and isotope information,including 14 water samples and5 gas samples.Geochemical analysis shows that the basic type of geothermal fluid is HCO₃-Na.The Na-K-Mg trigonometry and the SI values of some minerals indicate that the geothermal water has basically reached the water rock equilibrium state,and the geothermal water ions have similar change trend in Schoeller diagram,so it can be determined that the geothermal water is the same source.The abnormally high HCO^3-,F^-,and B³⁺indicate that the geothermal fluid has the characteristics of mantle source component,which can be seen in the stable carbon isotope?-0.94‰¹.63‰?of the fluid and the component of gas,indicating that the heat source in the study area may have convective heat in addition to conduction heat.The higher Li+and Sr/Ca indicate the presence of granite in the path of geothermal water transport.Hydrogen and oxygen isotopes in the study area are close to the local atmospheric precipitation,but T isotopes show the characteristics of modern water.Combined with the analysis of diagenesis in the study area,We think that the geothermal fluid is mainly a mixture of external atmospheric precipitation and sedimentary water.According to the analysis of geothermic ion characteristics and isotopes,the atmospheric precipitation supply is composed of local precipitation and surrounding mountain precipitation.According to the analysis of metamorphism coefficient?rNa⁺/rCl^-?,desulfurization coefficient(rSO₄^2-×100/rCl^-),magnesium-chloride coefficient(rCl^-/rMg²⁺)and silicon-enthalpy diagram,it is considered that the geothermal water in the study area was mixed by shallow groundwater in the rising process.It is estimated that the average reservoir temperature is 104?,and the geothermometer of Na-K,K-Mg and Na-K-Ca are applicable.The Cenozoic clastic strata are mainly developed in Yitong Basin.According to the analysis of physical property data and mercury injection data,it is considered that the physical property of Paleogene clastic rock in the study area is good and suitable for thermal reservoir.Yitong Basin has developed faults,and has good water supply and heat transfer channels.Finally,based on the analysis of geothermal genetic conditions and geothermal cycle characteristics,combined with the characteristics of stratigraphic framework in the study area,we established the geothermal genetic model of Yitong Basin.