Clarifying the geochemical characteristics of formation water and its origin is conducive to clarifying the gas migration path, elaborating the law of gas migration and accumulation, and further predicting the favourable area of gas accumulation. Taking Quaternary formation water from the Tainan-Sebei area of the Sanhu Depression as the research object, the chemical characteristics and origin of the region are clarified using anion analysis, cation analysis, hydrogen isotope analysis, oxygen isotope analysis and so on. The results are as follows. (1) The formation water in the study area has a high total dissolved solids (TDS) content and is mainly type IV and V of CaCl2. (2) Low r(Na+)/r(Cl−), low desulfurization coefficient, high r(Ca2+)/r(Mg2+) and high indices of base exchange indicate that the Qigequan Formation is in a stagnant zone, which is beneficial for the accumulation and preservation of biogenic gas. (3) Due to albitization and water–rock reactions, the formation water is rich in Ca2+, poor in Na+ and poor in Mg2+. (4) The formation water in the study area originates from the glacial meltwater of the Kunlun Mountains, which converts into groundwater and seeps into the formation along the piedmont slope zone. In the process of groundwater infiltration and convergence, many salt substances in the formation are dissolved, resulting in a gradual increase in TDS. Then, the formation water with a high TDS migrates to the anticline in the northern part of the depression and is finally trapped in the formation.

中文翻译：

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盐湖盆地地层水地球化学特征及成因——以柴达木盆地三湖凹陷第四系七各泉组为例

明确地层水地球化学特征及其来源，有利于明确天然气运移路径，阐明天然气运聚规律，进一步预测天然气聚集有利区。以三湖凹陷台南-涩北地区第四系地层水为研究对象，通过阴离子分析、阳离子分析、氢同位素分析、氧同位素分析等，明确该地区的化学特征和成因。结果如下。（1）研究区地层水总溶解固体（TDS）含量较高，主要为IV、V型CaCl2。(2) r(Na+)/r(Cl−)低、脱硫系数低、r(Ca2+)/r(Mg2+)高、碱交换指数高，表明七个泉组处于停滞区，有利于生物气的积累和保存。(3)由于钠长石化和水岩反应，地层水富Ca2+、贫Na+、贫Mg2+。（4）研究区地层水来源于昆仑山冰川融水，转化为地下水，沿山前斜坡带渗入地层。地下水在渗透汇聚的过程中，地层中的许多盐类物质被溶解，导致TDS逐渐增加。然后，TDS较高的地层水运移至凹陷北部的背斜，最终被困在地层中。