渤南洼陷古近系沙四段—沙三段烃源岩地球化学特征

Geochemical characteristics of Es_3-Es_4 source rocks in Eogene of Bonan Subsag

质谱和质谱-色谱分析结果表明，渤南洼陷古近系沙四段上亚段和沙三段中、下亚段烃源岩正构烷烃碳数分布多呈单峰型，主峰碳多为C21-C24，无明显奇偶优势。受构造运动和古气候因素的控制，两者形成于不同的沉积环境。沙四段上亚段烃源岩的Pr／Ph值低，而伽马蜡烷含量高，指示着半咸水-咸水甚至盐湖相的强还原水体环境；沙三段中、下亚段烃源岩的Pr／Ph值稍高，而伽马蜡烷含量较低，指示着淡水-微咸水的还原环境。奇偶优势比、碳优势指数、C32藿烷22S／（22S＋22R）、C29甾烷20S／（20S＋20R）和ββ／（αα＋ββ）等生物标志物参数表明，沙四段上亚段和沙三段中、下亚段烃源岩基本上达到成熟阶段，有利于油气生成。

GC and GC-MS analysis shows that carbon in normal paraffin hydrocarbons of mid-lower Es3 to upper Es4 source rocks in Eogene of Bonan Subsag displayed unimodal distribution with main peak from C21 to C24 without OEP values. Controlled by tectonic movement and paleoclimate, the two main source rocks were formed in different sedimentary paleoenvironments. The low value of Pr/Ph and the high gammacerane content indicate that the upper Es4 source rocks were generated in a strong reducing environment with brackish to saline facies. However,the relatively high value of Pr/Ph and low gammacerane content indicate that mid -lower Es3 source rocks were generated in reducing environment of fresh water to brackish water. Such biomarker parameters as OEP,CPI,22S/(22S +22R)of C32 hopane,20S/(20S+20R) and ββ/ (αα+ββ) of C29 sterane indicate that the source rocks of upper Es4 and mid-lower Es3 were basically mature and benefit to oil-gas generation.