川西坳陷上三叠统成藏年代学特征

Chronological characteristics of Upper Triassic reservoirs in western Sichuan depression

杨克明 叶军 吕正祥

Yang Keming Ye Jun Lü Zhengxiang

川西坳陷上三叠统可划分为两套生储盖组合:下部组合的生排烃高峰期为晚三叠世中晚期;上部组合的生排烃高峰期为晚侏罗世。导致须家河组储层致密化的原因:一是机械压实;二是自生矿物充填。须家河组储层致密化时期为中侏罗世上沙溪庙期末至晚白垩世。流体包裹体指示须家河组二段气藏的主要充注时期为须家河期须四时末至中侏罗世末。多期次的构造运动在川西坳陷形成了多期次的圈闭,以燕山期形成的大型古隆起与油气运聚匹配最好。综合源岩生排烃期、储层致密化期、流体充注储层时期、圈闭形成期,可以确定川西坳陷上三叠统的主要成藏期为印支中晚期—燕山中晚期。

The Upper Triassic in western Sichuan depression can be divided into 2 source-reservoir-cap rock combinations. The peak of hydrocarbon generation and expulsion in the lower combination occurred during middle-late stages of Late Triassic; while that in the upper combination occurred in Late Jurassic. Both mechanical compaction and infilling of authigenic minerals would have contributed to the tightening of reservoirs in Xujiahe Fm, which occurred at the end of the Middle Jurassic Upper Shaximiao through to Late Cretaceous. Analysis of fluid inclusions indicates that gas reservoirs in the 2 member of Xujiahe Fm were charged mainly at the end of the deposition of the 4 member of Xujiahe Fm through to the end of Middle Jurassic. Multiple phases of tectonic movements resulted in polyphase traps in western Sichuan depression, of which the large Yanshanian palaeohigh had the best timing with hydrocarbon migration and accumulation. Based on the stages of hydrocarbon generation and expulsion, tightening of reservoirs, fluid charging and trap formation, it can be determined that the main reservoiring stage in the Upper Triassic in western Sichuan depression would be from middle-late Indosinian to middle-late Yanshanian.

10.11743/ogg20050212