南羌塘盆地BK4井曲色组油页岩生物标志物异常组合现象及意义

Abnormal assemblage of biomarkers in oil shale and its significance in Well BK4,Quse Formation in South Qiangtang Basin

生物标志物的组合特征,是烃源岩沉积环境、有机质来源和有机质成熟度的综合反映。对南羌塘盆地BK4井曲色组油页岩的研究表明,显微组分组成中,存在较丰富的高等植物生源输入物,如镜质组、惰性组和壳质组,同时也存在较高丰富的无定形有机质,主要为腐殖无定形体。生物标志物组合特征的剖析表明,在化合物的来源特征上,具有高等植物来源意义的化合物的丰度较低,但与细菌生源有关的生物标志物丰度较高。在与沉积环境有关的生物标志物的组成与分布上,部分化合物表现为“海相或盐湖相”烃源岩的分布特点,如低的Pr/Ph值、高丰度的芳构化甲藻甾烷和硫芴系列化合物等。但在具有这些特征的烃源岩中,却含有异常高丰度的重排甾烷、高丰度的C29Ts和极低丰度的伽马蜡烷,也表现出一定的异常性;油页岩中高丰度细菌生源化合物的出现,说明生物化学作用阶段,细菌微生物的作用对生物标志物组合面貌具有重要影响。陆生和水生有机质来源和堆积过程的差异及生物化学作用过程的差异,可能是造成生物标志物异常组合现象的主要原因。

Assemblage characteristics of biomarkers are mainly related to the sedimentary environment,source input of organic matters and maturity of source rocks.The studies of organic petrology show that the organic compositions of oil shales in Well BK4,Quse Formation in South Qiangtang Basin are rich in macerals derived from higher plants,such as vitrinites,inertinites and exinites,and also high in amorphous organic matter,main⁃ly humic amorphogens.The analysis of biomarker compounds shows that the abundance of compounds with higher plant origin is lower,but the abundance of ones related to bacterial origin was higher.In terms of the com⁃position and distribution of biomarkers related to the sedimentary environment,some compounds show the dis⁃tribution characteristics of marine or saline lacustrine source rocks,such as low Pr/Ph value,high abundance of aromatic dinosteranes and dibenzothiophenes compounds.However,the source rock with these characteristics mentioned above contain abnormally high abundance diasteranes,high abundance C29Ts and extremely low abundance gammacerane,which also show some anomalies.The emergence of high abundance of bacterial bio⁃genic compounds in oil shale shows that the role of bacterial microorganisms in the biochemical stage has an im⁃portant influence on the combination of biomarker compounds.The differences in the sources and accumulation processes of terrestrial and aquatic organic matter and the differences in biochemical processes may be the main factors causing the abnormal assemblage of biomarkers.