川西坳陷新场地区上三叠统须家河组地层水成因探讨

川西新场地区上三叠统须家河组二段和四段地层水离子组合特征显示出海相地层水以及富溴泥页岩和煤层压释水侵入的特点,整体表现为富溴的压释水和海相地层水混合,原始沉积水和淡水的影响较小。由于海相地层水和富18O而贫氘的压释水对原始沉积水的侵入和替换,地层水的氘、氧同位素值增大。须四段地层水更为强烈的水岩反应造成其相对须二段地层水更高的氧同位素值这一反常现象。尽管Cl-、Na+、Br-等含量似乎只受控于地层水的混合,但是K+、Ca2+、Mg2+、和Fe2+、HCO3-、SO42-等变化则明显受水岩反应的控制,文中提出的成岩假设与须二段和须四段地层水中上述离子变化及前人的成岩研究相符,不同的水岩体系造成两者地层水化学特征的差异性,须四段更为开放的水岩反应体系使得其相对须二段地层水富Ca2+、Mg2+和Fe2+,但贫K+,这些离子差别可以很好地区分两者中的地层水。

A Discussion on Genesis of the Upper Triassic Xujiahe Formation Water in Xinchang Area,Western Sichuan Depression

The combination of ions of formation water from the Members 2 and 4 of the Upper Triassic Xujiahe Formation in Xinchang area, Western Sichuan depression, show the characteristics of water from marine strata, especially in the Cl~--Na~+-Br~-system, the water also show the mixture by bromine-rich compacting fluids from the adjacent shale and coal beds, and the enrichment of bromine can be used as a symbol of ballast water discharged, the modern formation water have been resulted from mixture of bromine-rich compacting fluids and water of marine. Because the connate water was flushed out of the sediments by compaction processes and replaced subsequently by younger compacting fluids and sea water,the values of the most samples significantly increased, especially for the water of the Member 4,the higher δ~(18)O value indicate the more intensive water-rock reactions compared to the Member 2. Although Cl~-, Na~+, Br~-concentration appears to be controlled by simple mixing rather than by diagenetic reaction, variation in K~+,Ca~(2+),Mg~(2+),Fe~(2+),HCO_3~-and SO_4~(2-)suggest diagenetic modification of both formation waters. The diagenetic reaction assumptions that is proposed for the variation above are in line with previous researches about the diagenesis. More open water-rock reaction system results in formation water of the Members 2 of the Xujiahe Formation being riched in Ca~(2+),Mg~(2+),Fe~(2+),but poor in K~+ compared to that of the Members 4 of the Xujiahe Formation water , by which both formation water can be distinguished from each other.