Study On The Difference Of DOM In Geothermal Water From Multi-thermal Reservoirs In Kaifeng

Dissolved organic matter(DOM)is very important to the chemical evolution of groundwater,and is a sensitive indicator of burial conditions,movement,chemical characteristics,and the geochemical environment of groundwater.Based on the exisiting research results and the geothermal well data that have been fully collected,the deep pore geothermal water in Kaifeng City is selected as the research object.According to the burial conditions,hydraulic characteristics and exploitation conditions of the geothermal water in Kaifeng City,the thermal reservoirs of Neogene Minghuazhen Formation and Guantao Formation with a depth of 600 m~1600 m are divided into five sub-thermal reservoirs(i.e.600 m to 800 m,800 m to 1000 m,1000 m to 1200 m,1200 m to 1400 m,1400 m to 1600 m).Geothermal water samples were collected from geothermal wells of different thermal reservoirs,respectively.The characteristics of hydrogen and oxygen isotopes in geothermal water and the difference of DOM are systematically analyzed.On this basis,according to the difference of DOM,the hydraulic relationship between geothermal water in differnet thermal reservoirs is analyzed,which provideds scientific support for the rational development,utilization and scientific protection of precious porous geothermal water in Kaifeng City.The mainachievements are as follows:(1)The burial distribution characteristics of five sub-thermal reservoirs in Kaifeng city are analyzed,including 600 m to 800 m,800 m to 1000 m,1000 m to 1200 m,1200 m to 1400 m,1400 m to 1600 m.The variation of hydrogen,oxygen and inorganic carbon isotopes in geothermal water of different sub-thermal reservoirs reveals the sources of groundwater recharge and the variation of inorganic carbon sources in geothermal water with depth.(2)The fluorescence components,fluorescence intensity and fluorescence peak positons of DOM in geothermal water of multi-thermal reservoirs in Kaifeng city were determined by using three-dimensional fluorescence spectroscopy technology.The sources of DOM and differences of DOM composition are analyzed.There is a certain difference in the fluorescence peak position of DOM in geothermal water with different depth.The fluorescence peaks of protein-like fluorescence and soluble microbial metabolites were observed at 600 m to1200 m,protein-like fluorescence and fulvic-like fluorescence at 1200 m to 1400 m,and fulvic-like fluorescence and humic-like fluorescence at 1400 m~1600 m.The results show that the source and composition of DOM in the same thermal reservoir are similar,but there are differences among different thermal reservoirs.(3)DOM in geothermal water was divided into three components by ultrafiltration: high molecular weight component DOM(>30KD),medium molecular weight component DOM(5KD~30KD)and low molecular weight component DOM(<5KD).The DOM contents and types of different molecular weight components in geothermal water with different depths were studied,and the formation mechanism and key influencing factors of DOM were identified.DOM in geothermal water with a depth less than 1200 m was mainly composed of medium molecular weight components,accounting for about half of DOM,while DOM in geothermal water with a depth more than 1200 m was mainly composed of high molecular weight components.(4)The PARAFAC model was applied to the classification and recognition of DOM of geothermal water in deep multi-thermal reservoirs in Kaifeng City,and the influence of parallel factor number on the analytical results of the model was studied.The results showed that the classification analysis of DOM's three-dimensional fluorescence spectrum was more suitable with a three-component parallel factor analysis model for the geothermal water with a depth of less than 1200 m,while the four-component parallel factor model was more suitable for the classification analysis of DOM's three-dimensional fluorescence spetrum than three-component parallel factor model for the geothermal water with a depth of more than 1200 m.