邦戈尔盆地中部凹陷烃源岩地球化学特征

Geochemical Characteristics of Source Rocks in Central Sag of Bongor Basin,Chad

利用大量烃源岩样品的有机地球化学分析资料,从烃源岩分布、沉积环境、有机质类型、有机质丰度、烃源岩生烃史以及生物标志物特征等方面,对邦戈尔盆地中部凹陷下白垩统烃源岩进行了综合研究,结果表明,研究区各层位暗色泥岩发育;有机质丰度高,整体为好烃源岩;有机质类型主要为Ⅱ1型;有效烃源岩主要为K组及其下部成熟烃源岩,成熟度为有效烃源岩的主控因素。生烃史模拟表明,K组及其下部的M组、P组烃源岩在晚白垩世及以前都进入过生烃高峰,具有较大的资源潜力,并且烃源岩没有二次生烃的可能。生物标志物分析表明,K组烃源岩沉积于半咸水-淡水、弱氧化-弱还原的湖相沉积环境,不同小层及构造位置其沉积环境有一定的差异。

The comprehensive research of the source rocks of the Lower Cretaceous in central sag of Bongor basin in Chad was conducted in this paper, based on the organic geochemical analysis data of the source rocks, from the aspects of source rock evaluation, history of the hydrocarbon generation and characteristics of the biomarkers, etc. The result indicates that the studied area is of characteristics of devel- oped dark mudstone, high abundance of organic matter, good source rocks, I1 ~ organic matter type, effective source rocks dominated by K formation and its below M and P formations, and maturity as the key controlling factor of effective source rocks. The result of the history simulation of hydrocarbon generation indicates that the source rocks of K, M and P formations even reach the peak stage of hydrocarbon generation in or earlier than the Late Cretaceous and have large potential of resources, and the secondary hydrocarbon generation is impossible. The biomarkers analYsis shows that the source rock of K formation deposits in fresh water-weak salt water and weak oxidation-weak reduction lacustrine sedimentary environment, but there are some differences in different layers and structural locations.