南堡凹陷Es_3~4段烃源岩有机地球化学特征及其油源贡献

南堡凹陷为环渤海湾盆地一个小而富油的生烃凹陷,勘探前景极为广阔,其中沙三段四亚段(Es_3~4)泥岩厚度大,分布范围广,为研究区最主要的烃源岩之一.通过对Es_3~4段烃源岩的有机岩石学与有机地球化学常规分析,对该套烃源岩系统的研究与评价,并且结合原油与烃源岩的生物标志化合物的对比与分析,探讨其油源贡献.研究结果表明,Es_3~4段部分层段生烃条件较好,有机质丰度与类型达到好烃源岩标准,依据生物标志化合物特征划分为2类,第一类烃源岩处于成熟阶段,主要形成于淡水的还原环境,生源构成为混合型,以低等水生生物和高等植物混源贡献为主;第二类烃源岩处于未熟一低熟阶段,主要形成于淡水氧化环境,以陆源高等植物输入为主,对油气贡献较少.油源对比结果表明,南堡凹陷高柳地区沙河街组的原油主要来源于Es_3~4段第一类烃源岩.

Geochemical Characteristics of Es_3~4 Source Rocks and Its Oil-source Contribution in Nanpu Sag, Bohai Bay Basin

The Nanpu sag is one of the oil-rich depressions in the Bohai Bay basin. The 4th section of the 3rd mem-ber of the Shahejie Formation (Es_3~4) is the organic-rich source rock, playing a very important role in hydrocarbon generation in the Nanpu sag. The contribution of Es_3~4 source rocks to petroleum reservoir has been discussed in this paper by evaluating source rocks and analyzing the geochemical features. The results show that the Es_3~4 source rocks have good generation condition with high organic carbon and good type of kerogen. The Es_3~4 source rocks are classi-fied into two types. The first type source rock is mature, deposited in a reducing environment, and originated from ordinary aquatic organisms and higher plants; the second type source rock is immature, deposited in a oxidation en-vironment, and originated from primarily higher plants with minor contribution for oil accumulation. Oil-source correlation shows that the oil in the Shahejie Formation in the Gaoliu area sourced from the type Ⅰ source rock.