鄂尔多斯盆地延长组葡萄藻的石油地质意义

鄂尔多斯盆地西峰地区中、上三叠统延长组发现极其丰富的葡萄藻化石.葡萄藻分布的高丰度层位恰好是本地区的主要烃源岩层延长组长7,2-长7,3段.葡萄藻不仅是烃源岩中藻类体和无定形体的重要组成部分,而且其丰度与有机碳含量成正比,表明葡萄藻是鄂尔多斯盆地三叠系延长组湖相优质烃源岩形成的重要母质.延长组原油和烃源岩中均检出特征极为相似的以补身烷、高补身烷为主的两环烷烃和以3位、4位甲基取代为特征的短链一长链单甲基支链烷烃.前一系列碳数分布在C12-C16,后一系列碳数分布在C15-C34.研究表明沉积物中这些生物标志物的出现与葡萄藻母质输入有关,进一步证明鄂尔多斯盆地三叠系延长组烃源岩及原油的形成与古湖泊中葡萄藻的大量发育有密切关系.图10参35

Petroleum geological significance of Botryococcus in Triassic Yanchang Formation, Ordos Basin

By microfossil analysis of the Middle and Upper Triassic in the Xifeng area of Ordos Basin, very abundant Botryococcus braunii have been found from the Yanchang Formation. The high-abundance strata of Botryococcus are members Chang 7-2 and Chang 7-3, which are the main source rock sections in the area. Botryococcus is an important component of the alginite and amorphogen in source rocks, and its abundance is in direct ratio to TOC content. The Botryococcus is an important biological source for the high quality terrestrial source rocks of the Triassic Yanchang Formation. C12-C16 bicyclic alkanes and C15-C34 monomethylalkanes were detected from both crude oil and source rocks in the Formation. These biomarkers from different samples have similar characteristics. The bicyclic alkanes are mainly homodrimane and drimane, and the methyl substituent positions of MMAs are 3 and 4. The studies show that these biomarkers in sediment are related to the parent material import of Botryococcus. Consequently, the hydrocarbon generation and source rock formation in the Triassic Yanchang Formation are closely related to the mass Botryococcus in the ancient lake of Ordos Basin area.