塔里木盆地库车坳陷东部煤系泥岩地球化学特征:对生烃母质和沉积环境的指示意义

Geochemical characteristics of coal measures mudstone in the eastern part of Kuqa Depression: Implication for parent material and sedimentary environment

库车坳陷东段侏罗系是目前塔里木盆地油气勘探的重点接替区之一,已发现油气与三叠系—侏罗系煤系泥岩密切关联。通过生物标志物、有机显微组分、元素地球化学等技术方法分区、分段对库车坳陷东段煤系泥岩母质与沉积环境进行表征。研究结果表明:三叠系—侏罗系煤系泥岩整体有机质丰度高,成熟演化处于成熟阶段,中侏罗统克孜勒努尔组3+4段煤系泥岩有机碳含量要高于下侏罗统阳霞组4段和三叠系塔里奇克组。通过母质来源与沉积环境的特征对比分析,与中侏罗统克孜勒努尔组相比,上三叠统塔里奇克组和下侏罗统阳霞组4段煤系泥岩中低等水生生物输入比例增加,更富氢,除具备很好的生气能力外,还具备一定的生油能力。上三叠统塔里奇克组到中侏罗统克孜勒努尔组沉积时期,水体还原性经历了由强到弱的演化过程,早期水体相对较深,具有一定盐度和还原性较好的沉积特征,中侏罗统克孜勒努尔组的富氧环境更利于煤系泥岩的发育。自西向东,三叠系—侏罗系煤系泥岩低等水生生物的贡献在增加,还原性增强、沉积速率降低,更利于有机质保存,生油条件更好,研究认识为区域油气源与分布规律认识提供重要支撑。

Jurassic in the eastern part of Kuqa Depression is one of the key replacement areas for oil and gas ex⁃ploration in Tarim Basin at present,and it has been found that oil and gas are closely related to Triassic-Jurassic coal measures mudstone.In this paper,the parent material and sedimentary environment of coal measures mud⁃stone in the eastern part of Kuqa Depression are described in three aspects:biomarkers,organic macerals and el⁃ement geochemistry.The research results show that the Triassic-Jurassic coal-measure mudstone has a high overall organic matter abundance,and its mature evolution is at a mature stage.The organic carbon content of coal-measure mudstone in the 3rd+4th members of Kezilenuer Formation,Middle Jurassic is higher than that in the 4th member of Yangxia Formation in Lower Jurassic and Taliqike Formation in Triassic.Through the comparative analysis of the characteristics of the source of parent material and sedimentary environment,com⁃pared with the Kezilenuer Formation in the Middle Jurassic,the input ratio of lower aquatic organisms in the coal measures mudstone of the Taliqike Formation in the Late Triassic and the 4th member of the Yangxia For⁃mation in the Lower Jurassic increased.They are rich in hydrogen,and have good gas-generating ability and cer⁃tain oil-generating ability.During the sedimentary period from the Upper Triassic Taliqike Formation to the Middle Jurassic Kezilenuer Formation,the reducibility of water body experienced an evolution process from strong to weak.In the early stage,the water body was relatively deep,with a certain salinity and good reducibil⁃ity,and the oxygen-rich environment of the Middle Jurassic Kezilenuer Formation was more conducive to the development of coal measures mudstone.From west to east,the contribution of lower aquatic organisms such as Triassic-Jurassic coal measures mudstone increases,with strong reducibility and lower sedimentation rate,which is more conducive to the preservation of organic matter and better oil-generating conditions.The research and understanding provide important support for the understanding of regional oil and gas sources and distribu⁃tion laws.