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The Geochemical Characteristics and Origin of Deep Geothermal Water in Baxian Sag, China

Abstract

Located in the north of Jizhong Depression, the Baxian Sag is rich in geothermal resources. The geochemical characteristics and origin of three deep hot water reservoirs(Guantao Formation, Dongying Formation, the second-third member of the Shahejie Formation) in Baxian Sag haved been studied by the temperature and chemical analysis of formation water. The results show that three types of deep hot water have been found. The first type hot water(I) with lower total dissolved solids(<5g/l) is mainly in Guantao Formation(Ng), the main anionic are Cl- and HCO3- and the main cationic is Na+, hydrochemical type is Cl-HCO3-Na. Based on the above dates, the first type hot water which is in open hydrogeochemical environment is mainly from atmospheric infiltration water. The second type(II) hot water with higher total dissolved solids(5-40g/l) is mainly in Dongying Formation (Ed) and the second-third member of the Shahejie formation(Es2+3), the main anionic is Cl- and the main cationic is Na+, hydrochemical type is Cl-Na. The second type of hot water which is in semi-closed hydrogeochemical environment is mainly from the mixture of deposition water with atmospheric infiltration water and evaporation concentration effect plays an important part role during the formation of this type of hot water. The third type (III)of hot water with the highest total dissolved solids(>40g/l) is also mainly in Dongying Formation(Ed) and the second-third member of the Shahejie formation(Es2+3), the main anionic is Cl- and the main cationic are Na+ and Ca2+, hydrochemical type is Cl-Na-Ca. The third type of hot water which is in closed hydrogeochemical environment is mainly from deposition water and plagioclase albitization effect plays an important part role during the formation of the third type of hot water. With the burial depth increment, the hot water changed from type I to type II and then type III. With the temperature increment of the hot water, the water-rock interaction becomes increasingly intensive and the mineralization degree get higher, resulting in a transition of the water chemical type, e.g., (rNa/rCl) and the (rSO4×100/rCl) turn lower while (r(Cl-Na)/rMg) gets higher.