Geochemical Characteristics of Gas Field Water and Sources of Lithium from Majiagou Formation in Jingbian Area of Ordos Basin,China
The gas field water of Majiagou Famation in Jingbian area of Ordos Basin has a high Li+concentration,the lithium in some gas field water has reached industrial grade with great potential for development.However,the sources of lithium from the gas field water is still unclear.According to thin section identification,X-ray diffraction analysis,trace element analysis,Sr and Li isotope analysis,the geochemical characteristics of gas field water in Majiagou Formation and the sources of lithium were studied.The results show that ① the ion concentration in the gas field water varies greatly,and the salinity degree ranges from 0.12 to 228.19 g·L-1 with an average of 39.87 g·L-1;partial water bodies reach the category of brine,and the pH value ranges from 4.82 to 8.44,mainly weakly acidic;the hydrochemical type is mainly CaCl2-type while some wells are MgCl2-type or NaHCO3-type.② The sodio-chlorine coefficient of gas field water is generally greater than 0.87,the desulfurization coefficient is generally less than 1,the metamorphism coefficient is generally greater than 0,and the chloro-magnesium coefficient mainly ranges from 20 to 90;the reservoir as a whole has a good sealing property,the water has a strong reducibility and high degree of metamorphism,which belongs to the high metamorphism and concentration water body;the sealing condition of reservoir in some wells is damaged and obviously affected by atmospheric water.③ The Li isotope of gas field water has the characteristics of Early Ordovician sea water,while the Sr isotope is affected by the tuff compositions as well as the karst of atmospheric water,and the 87Sr/86Sr value is higher than that of the normal sea water in the sedimentary period of Majiagou Formation.④ The tuffaceous rocks and karst breccia interstitial material of Majiagou Formation generally have high Li+concentration.Li isotopic characteristics indicate that Li+in gas field water mainly comes from Majiagou Formation,the Li-rich gas field water is the results of burial and evolution of underground karst water of Caledonian in Majiagou Formation.
gas field waterlithiumsalinity degreechemical coefficientisotopematerial sourceJingbian areaOrdos Basin
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