柴达木盆地乌南-绿草滩地区烃源岩地球化学特征

Geochemical Characteristics of the Source Rocks from Wunan-Lücaotan area in Qaidam Basin

依据烃源岩有机质丰度、有机质类型和有机质成熟度分析,发现乌南—绿草滩地区较好—好烃源岩主要分布在下干柴沟组上段和下干柴沟组下段。烃源岩生物标志化合物主要特征为正烷烃系列中—低碳数(15～19)出现偶碳数优势,高碳数(25～29)表现为奇数碳优势。萜类化合物表现出高伽马蜡烷—高三环萜和低伽马蜡烷—低三环萜2种类型,C34、C35升霍烷含量较低,甾烷既有C27优势,也有C29优势。反映烃源岩发育区主要处在深湖相带与滨浅湖相带之间的过渡相带,水生生物与陆源高等植物有机质生源各有一定比例。值得关注的是,在绿参1井不同深度的5个古近系—新近系烃源岩样品,在其芳烃馏分中均检测到三联苯系列化合物,发现三联苯系列中不同取代位置的同分异构体相对含量和烃源岩中有机质的热演化程度表现出很好的正相关性,成为氯仿沥青"A"芳烃馏分中判识烃源岩有机质热演化程度的有意义参数。

According to abundance and＇type of organic matter and its thermal maturity, we consider that the upper and lower sections of lower Ganchaigou Formation belonged to good and better source rock. The bio- marker features of n-alkenes for source rocks show an even-to-odd （15-19） and odd-to-even （25-29） predominance. Terpenoids are characterized as high 7- and tricyclic diterpene,low 7- and tricyclic diterpene, low abundance of Ca4 and C35 hopanes,and C27〉C29 or C29〉C27 for steranes. All of geochemical parameters suggest that the organic matter was derived from aquatic organisms and higher plants in the transition zone between deep and shallow lacustrine depositional settings. It should be noted that the occurrence of one terphenyl compounds in the aromatic hydrocarbons from 5 source rocks （Lucan 1 well） sampling at different depth,and the relative abundance of each isomers is positively related to thermal maturity, 20S/（20S＋ 20R） ratio of C29 steranes,and Ro values. So the relative abundance of each isomer would be a potential parameter for indicating thermal maturity of organic matter.