延吉盆地白垩系未熟油的生成与特征

Generation and feature of the Cretaceous immature oil in Yanji basin.

吉林省延吉盆地白垩系未熟油目前主要见于德新凹陷大拉子组，埋深小于１０００ｍ，与同盆地的成熟油相比，芳烃和沥青质含量相似，而饱和烃含量低、非烃含量高，组分碳同位素轻（小于－３０‰），Ｃ２９２０Ｓ／（２０Ｓ＋２０Ｒ）值小于０．３５，Ｃ２９ββ／（ββ＋αα）值小于０．２５，烃转化率相近或略低。认为该盆地未熟油生成阶段的Ｒｏ值为０．３％～０．６％。建立了未熟油的生油模式。根据油源对比，德新凹陷未熟油主要来源于大三段和大一段油源岩。从原油γ蜡烷含量推断，未熟油源岩可能形成于咸水—半咸水环境；据原油∑Ｃ２７甾烷／∑Ｃ２９甾烷的值判断，未熟油的湖相生物贡献多于成熟油。盆地的未熟油重点勘探地区应是东部的德新凹陷和清茶馆凹陷。

Cretaceous immature oil in Yanji basin, Jilin province, appears mainly in Dalazi Group in Dexin sag at a depth less than 1000m. Compared with the mature oil discovered in the same basin, its aromatic and asphaltic contents are similar each other while non hydrocarbon content is higher; it's carbon isotope is relatively light, C 29 20S/(20S+20R) less than 0.35, C 29 ββ/(ββ+αα ) less than 0.25 and their transformation ratio is similar or somewhat lower. It is recognized that the immature oil generated at a period R o is 0.3% 0.6%. Model of immature oil generation is established. From a oil source correlation the immature oil in Dexin sag came mainly from source rocks in Da 3 and Da 1 sections. Deducted from the γ paraffin content, the oil source rocks might be deposited in a brackish environment. From ∑C 27 sterane/∑C 29 sterane in the crude lacustrine biogenic contribution is higher in immature oil than that in the mature oil. The district for prospecting the immature oil should be Dexin and Qingchaguan sags in the eastern part of the basin.