四川盆地乐山-龙女寺古隆起震旦系天然气成藏特征

Hydrocarbon accumulation of Sinian natural gas reservoirs,Leshan-Longnüsi paleohigh,Sichuan Basin,SW China

以四川盆地乐山—龙女寺古隆起震旦系古老碳酸盐岩气藏为研究对象,通过系统分析气藏储集层、天然气组分及气藏类型、油气成藏条件与成藏演化等,研究了震旦系古老碳酸盐岩气藏成藏过程。乐山—龙女寺古隆起震旦系灯影组已发现6个气藏,气藏储集岩类、储集层类型基本一致,均具有高温、常压、强非均质性特征,但不同层段气藏类型、古隆起不同部位气藏天然气组成及碳同位素组成等方面具有明显差异。古隆起震旦系灯影组天然气属于油裂解气,主要为灯影组自身烃源岩与寒武系筇竹寺组烃源岩的混源气,良好的烃源岩、储集层、源储组合与输导条件决定了灯影组气藏的形成和保存。古隆起区灯影组气藏的形成经历了古油藏生成、古油藏裂解、气藏的调整与定型3个阶段,受古隆起形成及不同部位构造差异演化影响,气藏形成具有3种不同的天然气聚集成藏过程。

The old Sinian carbonate reservoir in the Leshan-Longnüsi paleohigh was taken as a research object to study the process of gas accumulation in the Sinian reservoir through analysis of gas reservoir characteristics, gas composition, gas reservoir types, accumulation condition and evolution. The results show that the reservoir lithology and type are almost the same in the six gas pools discovered in the Leshan-Longniisi paleohigh. All the gas reservoirs are characterized by high temperature, ordinary pressure, and intense heterogeneity. The gas reservoir type in different layers and the gas compositions and carbon isotopes in different locations vary obviously. The gas of Sinian Dengying Formation, originated from oil cracking, is mixed gas mainly from source rocks of Sinian Dengying Formation as well as Cambrian Qiongzhusi Formation. The source and reservoir condition, their combination and fluid transporting conditions are favorable, which can determine the gas accumulation and preservation in Dengying Formation. The Sinian gas reservoirs are believed to have been accumulated by the following processes： paleo-oil accumulation, paleo-oil cracking, and gas reservoir adjustment and finalization. There are three processes of gas accumulation in the reservoir, which are influenced by the formation of paleohigh and differential structural evolution in different positions.