川东北地区普光气田成藏模式研究

普光气藏天然气常规组成呈甲烷含量高、乙烷和丙烷等重烃含量低的组份特征,干燥系数C1/(C1—C5)介于0.989 6～0.999 6之间,明显属晚期裂解干气类型。普光古油藏的油源主要来自下志留统以及二叠系有效烃源岩,现今气藏气源主要来自古油藏原油的二次裂解以及下志留统、二叠系源岩干酪根的热裂解,现存沥青对普光气藏也有一定的贡献。普光气藏储集层主要发育于下三叠统飞仙关组一—三段及上二叠统长兴组上部,为溶孔白云岩、砂屑白云岩、鲕粒白云岩、含砾屑鲕粒白云岩及糖粒状白云岩,鲕粒白云岩属层状孔隙溶孔型储层。气藏盖层主要为该区下三叠统嘉陵江组二段、四段及其上的中三叠统雷口坡组膏盐层,构成了本区良好保存条件的重要因素。普光气藏属于构造—岩性复合气藏,气藏存在3期烃类流体注入;成藏模式可归纳为"多期成藏,油气转化,晚期定位"。

THE EVOLUTION MODLE OF THE PUGUANG GAS FIELD IN NORTHEAST OF SICHUAN

The composition of gas in the Puguang gas field shows that methane is high and hexane,propane and heavier hydrocarbon are low,and coefficient of gas desiccation(C₁/C₁-C₅) is 0.989 6～0.999 6,clearly,the gas is the type of split gas.The oil was from the sources rocks of Lower Silurian and Permian,and formed the oil field during Late Triassic to Jurassic,The gas in the field is from the split gas of the oil field and the kerogen in the sources rock.The bitumen in the reservoirs little contributes to the gas.The reservoirs in gas field developed in the first to third secters of the Feixianguang Formation,upper Chang-xing Formation,which are the Lower Triassic and Upper Permian respectively,and the rocks are dissolved pore dolomite,doloarenite,oolite dolomite,oolite dolorudite and saccharoidal dolomite.The seal covers are mainly gyps and salt rocks,which developed in the second and fourth secter of the Jialingjiang Formation in Lower Triassic and the Leikoupo Formation in Middle Triassic,it is impotent factor to prevent the gas leak in the field.The gas field is a structure-lithology reservoir.There were three times of oil and gas migration and accumulation.The modle would be "multi-accumulation,oil spilted to gas,located in later stage".