四川盆地新场构造带上三叠统须家河组二段地层水化学动态特征及其成因

四川盆地新场构造带须家河组二段(须二段)地层水化学特征复杂,矿化度分布范围广,部分井在生产过程中地层水化学特征发生动态变化.因此,利用矿化度、氯镁系数、变质系数和诺瓦克相图等分析了须家河组各层段地层水化学特征,探讨了地层水的动态运移.结果显示:须二段地层水矿化度主要集中在70～110 g/L,氯镁系数大于50,变质系数...

Dynamic chemical characteristics and origin of formation water in the second member of Xujiahe Formation,Xinchang structural belt,Sichuan Basin

Formation water from the second member of Xujiahe Formation, Xinchang structural belt, Sichuan Basin, is chemically complicated and highly variable in salinity, with some wells recording dynamic changes of chemical characteristics of produced waters.This paper discusses the migration of formation water based on a thorough analysis of the chemical characteristics of formation water from each interval of the Xujiahe Formation by using salinity data, chlorine/magnesiumionic ratios, metamorphism coefficients, Novák's phase diagrams and etc. The results show that the formation water of the second member has salinity values ranging between 70 and 110 g/L, chlorine/magnesium ionic ratios greater than 50 and metamorphic coefficients greater than 10; and that of the fourth member has salinity values ranging between 50 and 90 g/L, chlorine/magnesium ionic ratios less than 50 and metamorphism coefficients less than 10.Their Novak's phase diagrams also have obvious differences.These characteristics can be used to determine the stratigraphic origins of formation waters.The produced water from most wells in the second member show relatively stable chemical characteristics, indicating that the waters are sourced from the same stratigraphic interval. However, the produced water from some wells, such as Xin 856, Xin 2, Xin 10-1H and Xin 5, show significant variation of chemical characteristics. Judging by the graphs, the waters are multi-sourced. Alien waters of high salinity and high bromide ion concentration from marine Leikoupo Formation had been detected in wells Xin 2 and Xin 856 after Wenchuan Earthquake. Waters from the fourth member were also observed in wells Xin 10-1H and Xin 5.It is suggested that faults are the most likely pathways for this cross-layer migration of formation water.