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海侵事件是松辽盆地的重要地质事件之一，其主要特征是存在着甲藻甾烷和Ｃ３１甾烷。朝长地区长２０井原油为典型的未熟低熟油。油源对比表明：未熟低熟油的源岩与白垩系青山口组一段海侵地层有关，因而说明油气的早期生成与海侵事件密切相关。海侵地层之所以能生成油气，特别是生成低熟油气有如下原因：①伴随着海侵高水位阶段常能形成有机质丰度较高的源岩，这是油气形成的物质基础；②海侵阶段形成的生油岩和海退阶段形成的储层的有机配合，有利于油气的赋存；③海侵常能使水体的盐度增加，造成某些藻类生物的发育，形成有机质类型较好的源岩；④海侵地层中的半咸水咸水藻类具有丰富的生物类脂物，聚合程度低，在早期阶段可以形成低熟油气。
The transgression event is one of the important geological events in the Songliao Basin. Its main feature is the presence of dinosterane and C31 sterane. Chang-20 long well in the region as a typical crude oil cooked low-cooked oil. The comparison of oil sources shows that the source rock of the immature low mature oil is related to the transgressive formation of the Cretaceous Qingshankou Formation, indicating that the early hydrocarbon generation is closely related to the transgression event. The reason why the transgressive formations can generate oil and gas, in particular, the generation of low-mature oil and gas are as follows: ① The source rocks with high abundance of organic matter can often form along with the stage of transgression and high water level, which is the material basis for the formation of oil and gas. The organic combination of the source rock formed in the stage and the reservoir formed in the regression stage is conducive to the occurrence of oil and gas. ③ Sea transgression often increases the salinity of the water body, resulting in the development of certain algal organisms and the formation of better organic matter types Of the source rocks; ④ brackish water in the transgression strata of saline water algae are rich in biological lipids, the degree of polymerization is low, in the early stages of the formation of low-mature oil and gas.