渤南洼陷沙四下段红层原油地球化学特征及油源探讨

Geochemical Characteristics and Oil Origin of Crude Oil in Red Beds of the Lower of Es_4 in Bonan Subsag

根据GC、GC-MS等分析结果表明,渤南洼陷沙河街组四段下亚段原油正构烷烃分布呈单峰形态,高碳数C22—C34范围内具有明显偶碳优势,类异戊二烯烷烃呈植烷优势,伽马蜡烷、4-甲基甾烷、孕甾烷和升孕甾烷含量较高,重排甾烷不发育,C35升藿烷丰度明显高于C34升藿烷,芳烃中三芳甾烷的含量较高,三芴系列中硫芴含量丰富,均表明源岩沉积于富硫的强还原的半咸化—咸化湖相环境,并且C2920S/(20S+20R)值分布在0.49~0.55之间,属于典型的成熟油。通过油源对比认为沙河街组四段下亚段红层原油来自该区沙河街组四段上亚段烃源岩。

GC and GC-MS analysis of the extracts show that the distribution of normal alkane of crude oil in red beds in the lower part of the fourth member of Shahejie Formation appears as single-peak type,the even carbon advantage obviously from high carbon numbers C22 to C34,isoprenoid alkanes exhibits a phytane predominance,relatively high contents of gammacerane,4-methyl steranes,pregnane and sublimation-pregnane.The content of rearranged sterane is very low,and the C35 homohopane content is higher than C34 homohopane.Triaromatic sterane content is higher in aromatic hydrocarbon,and dibenzothiophen presents in abundance in benzfhiore tri-fluorene,which show that the source rock was deposited in strong reducing environment with a large amount of sulfur in brackish-saline lake,and C2920S/(20S+20R)value ranging from 0.49 to 0.55,indicate it is a typical mature oil,and crude oil in red beds is derived from source rock of the upper part of Es4 on the basis of oil-source correlation in Bonan Subsag.