中非裂谷系Muglad盆地下白垩统烃源岩非均质性及其启示

Organic Geochemical Heterogeneity of Lower Cretaceous Source Rock in Muglad Basin,Central African Rift System and Its Implications for Petroleum Exploration

为了进一步刻画中非裂谷系Muglad盆地下白垩统Abu Gabra组烃源岩的垂向有机地球化学非均质性,将Abu Gabra组划分为了4个层段,即AG_(1)、AG_(1)^(2)、AG_(2)^(2)和AG_(3),对其进行总有机碳和岩石热解实验分析,结果表明,AG_(1)和AG_(1)^(2)烃源岩的有机质丰度较低,干酪根类型以Ⅱ2-Ⅲ型为主,热成熟度普遍偏低;而AG_(2)^(2)和AG_(3)烃源岩有机质丰度高,干酪根类型以Ⅰ-Ⅱ1型为主,且正处于主要生油窗阶段。基于原油与AG_(1)、AG_(1)^(2)、AG_(2)^(2)和AG_(3)代表性烃源岩有机质中生物标志化合物的对比发现,原油与AG_(2)^(2)、AG_(3)烃源岩具有很好的可比性,而完全不同于AG_(1)和AG_(1)^(2)烃源岩。据此可知,AG_(2)^(2)和AG_(3)烃源岩是Muglad盆地已发现油气聚集的主力供烃层段,而AG_(1)和AG_(1)^(2)烃源岩的贡献有限。

In order to further characterize the vertical organic geochemical heterogeneity of the hydrocarbon source rocks of the Abu Gabra Formation of the Lower Cretaceous in the Muglad Basin of the Central African Rift System,the Abu Gabra Formation is divided into four intervals from top to bottom,namely AG_(1),AG_(1)^(2),AG_(2)^(2)and AG_(3),and their total organic carbon and rock pyrolysis are analyzed by experiments.The results show that the abundance of organic matter in AG_(1)and AG_(1)^(2)source rocks is relatively low,the kerogen is mainlyⅡ2-Ⅲtype,and the thermal maturity is generally low;However,the organic matter abundance of AG_(2)^(2)and AG_(3)source rocks is high,and the kerogen is dominated by I-Ⅱ1 type,which is in the main oil generation window stage.Based on the comparison of the biomarkers in crude oils and AG_(1)、AG 21、AG_(2)^(2)and AG_(3)source rocks,it is found that the crude oils have good consistency with AG_(2)^(2)and AG_(3)source rocks,but are completely different from AG_(1)and AG 21 source rocks.It can be seen from this that the current oil accumulations in the Muglad Basin are mainly generated from the AG_(2)^(2)and AG_(3)source rocks,and the contribution of AG_(1)and AG 21 source rocks is limited.