Analysis Of Hydrogeochemical Characteristics Of Underground Hot Water In Hunan Province

With the ultra-rapid development of the world economy and the increasing consumption of non-renewable energy sources such as fossil fuels,more and more scientific and technological goals are developing towards renewable green energy.Geothermal resources are water resources with high temperature and rich ion content,which is a kind of renewable green energy.It has brought huge economic benefits to people,especially in energy utilization,medical value,leisure and entertainment.However,how to make reasonable and sustainable use of geothermal resources is the main current issue.Hunan Province has abundant geothermal water resources,but the degree of hydrochemistry research is not high.In order to analyze and ascertain the occurrence of geothermal water in Hunan Province,the characteristics of ion content,hydrochemical type,the supply source of geothermal water,the estimation of the temperature of the heat storage in the study area,the mixing ratio of cold and hot water,and the depth of hot water circulation,etc.Ion ratio method,PHREEQC calculation of mineral saturation,stable hydrogen and oxygen isotope method,and silicon enthalpy model are used to conduct hydrogeochemical analysis on69 geothermal water in the study area.The results show that the main hydrochemical types of geothermal water in Hunan Province are HCO3-Ca and HCO3-Ca·Mg,followed by SO4·HCO3-Ca·Mg and SO4-Ca,the characteristics of sodium ion and chloride ion content,and the characteristics of calcium and magnesium ions.The ratio reflects the long storage time of geothermal water in Hunan Province and the long runoff path.The Cl-SO4-HCO3 triangle diagram shows that the geothermal water in the study area is in the form of hot steam-type geothermal water rich in HCO3^-peripheral water properties and a small part of SO4^2-;the Na-K-Mg triangle diagram shows the geothermal energy in Hunan Province Water is basically"immature"water,which is not suitable for the cationic temperature scale to estimate the heat storage temperature;the PHREEQC is used to calculate the multi-mineral saturation index,and the quartz silica mineral is closest to the saturated state.The silicon-enthalpy mixing model estimates the study area Heat storage temperature and cold water mixing ratio,the results show that the heat storage temperature range is 32??226?,the average value is 140?,and the cold water mixing ratio is 85%on average,which is relatively large;the geothermal gradient is used to calculate the geothermal water circulation depth range as 0.56?10.6km,with an average depth of 5.34km.By studying the hydrogen and oxygen isotope characteristics of geothermal water in Hunan Province,analyzing the source of geothermal water supply,the drift of ¹⁸O and the strength of the water-rock interaction of the geothermal water,the source of geothermal water supply and the formation environment are obtained.The degree of interaction with water and rock is basically similar.The?D and?¹⁸O values are mostly distributed near the regional atmospheric precipitation line,indicating that the main source of geothermal water supply in Hunan Province is atmospheric precipitation.The deuterium excess d value of each structural unit is almost smaller than the intercept of the regional atmospheric precipitation equation,indicating that the degree of water-rock interaction of the geothermal water in Hunan Province is relatively strong,and the strong water-rock interaction increases the drift of ¹⁸O,which explains The reasons why the values of?D and?¹⁸O deviate from the atmospheric precipitation line are discussed.The geothermal water in Hunan Province has a long evolution time,a relatively long runoff time,and a large regional circulation depth.After the hydrothermal fluid is warmed by the heat storage,after a long period of runoff,water-rock interaction,etc.,the geothermal water is driven by high pressure and thermodynamics to heat the geothermal energy.The water circulates to the surface and mixes with cold water near the surface to form"immature"medium-low temperature hot water with low temperature as the mainstay.