川中地区须家河组致密砂岩气成藏机理

以四川盆地川中地区上三叠统须家河组致密砂岩气藏为例,探讨其成藏过程及成藏机理。通过对川中地区典型构造单井的生烃史模拟发现,不同构造须家河组烃源岩的生烃过程整体上具有相似性。经包裹体均一温度、自生矿物K-Ar法测定年龄和裂缝充填矿物ESR法测定年龄确定了川中地区须家河组油气成藏的3个期次,前2期分别为侏罗纪期间成熟和高成熟的烃类流体向储层中的充注,后一期为晚白垩世以来的构造隆升调整,对早期天然气藏改造并再次成藏的过程。川中地区须家河组致密砂岩天然气成藏具有三大特点:天然气近距离运移;天然气以游离相充注为主;隆升过程中天然气的泄压膨胀对天然气成藏具有重要贡献。

Accumulation mechanism of the compacted sandstone gas in Xujiahe Formation of Central Sichuan in China

Taking the compacted sandstone gas accumulation in Upper Triassic Xujiahe Formation of the middle area of Sichuan as example,this paper discusses the process and mechanism of the compacted sandstone gas accumulation and provides the evidences for the next pace of exploration and exploitation of this sandstone gas accumulation.Through simulating the hydrocarbon-generating history of the typical structure in the middle area of Sichuan,it can be concluded that the generation process of the source rocks in Xujiahe Formation with different structures have some similarities as a whole.By the method of fluid inclusions’ homogeneous temperature,K-Ar dating method of authigenic minerals and ESR dating method of crack filling minerals,the three periods of the gas accumulation are determined in Xujiahe Formation of the middle area of Sichuan.The former two periods were mature and highly mature hydrocarbons filling into the reservoir in Jurassic,and the last period had been the structure’s uplifting and adjusting period since Late Cretaceous,which transformed the early natural gas reservoir and then made it accumulated again.By and large,the compacted sandstone gas has three characteristics in Xujiahe Formation of Middle Sichuan area.First,the migration distance of the natural gas is short,second,the filling form of the natural gas is in free phase,and thirdly,the decompression and inflation of the natural gas plays an essential role in the natural gas accumulation in the process of uplift.