非洲喀土穆盆地下白垩统烃源岩特征与油气成藏  

Source rock characteristics and hydrocarbon accumulation from the Lower Cretaceous in the Khartoum basin, Africa

作　　者：张新顺[1] 张光亚[1] 王克铭 王利[1] 余朝华[1] 何军[1] ZHANG Xin-shun;ZHANG Guang-ya;WANG Ke-ming;WANG Li;YU Zhao-hua;HE Jun(PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China)

机构地区：[1]中国石油勘探开发研究院,北京100083

出　　处：《地球化学》2021年第6期612-622,共11页Geochimica

基　　金：中石油集团科技专项(2021DJ3103);海外风险勘探研究课题(2021-167)。

摘　　要：喀土穆盆地是一个中新生代裂谷盆地,位于中非裂谷系最东端,盆内发育十多个凹陷。本次研究基于岩屑和原油样品的地球化学分析,重点对盆地内K凹陷和D凹陷下白垩统烃源岩进行研究。结果表明,K凹陷下白垩统AJ组发育一套较为优质的湖相泥岩,厚度为40~180m,以Ⅱ型有机质为主,整体热演化为低熟-成熟阶段;AJ组泥岩的姥植比多为0.5~2之间,属于半还原-半氧化环境,有机质以半咸水湖泊中水体生物和陆源高等植物混源为主。而D凹陷的下白垩统D3组发育一套中等到好的气源岩,以Ⅱ2~Ⅲ型有机质为主,整体热演化为成熟-高成熟阶段,总有机碳比AJ组稍低,但厚度很大在200~500 m之间。从K凹陷向南到D凹陷,有机质中高等植物来源占比增高,藻类和细菌来源有机质占比降低,盆地中原油的萜烷和甾烷含量均较低,藿烷含量高,具有典型的中非裂谷系原油特征。结合有机质类型和成熟度,喀土穆盆地K凹陷未来勘探应以油为主, D凹陷以气为主,其余凹陷潜力有限。The Khartoum basin is a Mesozoic-Cenozoic rift basin, located in the eastern Central African rift system.There are more than ten depressions in the basin. Based on the geochemical analysis of debris and crude oil samples,this paper focuses on the study of the Lower Cretaceous source rocks in the Khartoum and Dinder depressions.The results show that a set of high-quality lacustrine mudstones with thickness of 40–180 m developed in the Abu Jin formation of the lower Cretaceous in the Khartoum depression and are mainly type II organic matter;their overall thermal evolution is in a low maturity stage. The ratio of basking to planting of the mudstones in the Abu Jin formation is mostly between 0.5 and 2, which denotes an environment of semi-reduction and semi-oxidation,and the organic matter consists mainly of aquatic organisms from a semi-salt water lake, interjected by some terrestrial higher plants. The Dinder III formation of the lower Cretaceous in the Dinder depression developed a set of medium to good gas source rocks, which are dominated by type II2–III organic matter. The overall thermal evolution is at a high maturity stage. The total organic carbon(TOC) is slightly lower than that of the Abu Jin formation, but it is very thick, at 200–500 m. From the Khartoum depression to the Dinder depression, the proportion of organic matter from higher plants increased, whereas that from algae and bacteria decreased. The content of terpane and sterane in the crude oil in the basin was low, and the content of hopane was high, which are typical characteristics of Central African rift system crude oil. Combined with the type and maturity of organic matter, the future exploration of the Khartoum depression in the Khartoum basin should be dominated by oil, whereas that of the Dinder depression should be dominated by gas. However, the other depressions have limited potential.

关 键 词：K凹陷 D凹陷 下白垩统 烃源岩 中非裂谷系 喀土穆盆地 

分 类 号：P593[天文地球—地球化学] TE122.1[天文地球—地质学]