埃塞俄比亚欧加登盆地石油地质特征与勘探方向

Petroleum Geological Characteristics and Exploration Potential of Ogaden Basin in Ethiopia

埃塞俄比亚欧加登盆地是非洲东海岸油气勘探前景最好的盆地之一,虽历经多年勘探,但仍处于早期评价阶段,勘探方向和选区并不明确。通过对盆地结构、烃源岩特征和油气成因的研究,结合大地构造学理论,明确了盆地演化历程、构造区划及沉积充填特征,阐述了三套有利含油气系统的特征,指明了具体的有利勘探方向。研究表明:欧加登盆地的构造演化主要受控于大陆板块的裂解、漂移与洋壳的扩张,经历了四个构造演化阶段,形成了"下断上坳"的沉积充填结构;发育三叠系、中侏罗统、上侏罗统—下白垩统三套含油气系统,其中三叠系、中侏罗统含油气系统最为有利,其主力烃源岩层Bokh组发育深灰色、黑灰色泥岩,有机质含量高,演化程度高;位于西部凹陷和中部凹陷之间的中央凸起地层齐全,并发育多种类型正向构造,是油气运移的重要指向区,成藏条件最好,应根据三叠系、中侏罗统含油气系统的特点,围绕中央凸起寻找勘探目标,是目前扩展盆地勘探局面最现实的方法。

The Ogaden Basin in Ethiopia is one of the most promising oil and gas exploration ones in the east coast of Africa.It has still at early evaluation stage although it goes through years of exploration.Explo-ration potential and targets are not clear.Based on the study of basin structure,hydrocarbon source rock characteristics and hydrocarbon genesis,combined with geotectonics theory,the basin evolution,tectonic zoning and sedimentary filling characteristics are clarified,the characteristics of three sets of favorable petroleum systems are expounded,and the specific favorable exploration target is pointed out.The results show that the tectonic evolution of the Ogaden Basin is mainly controlled by the cracking and drifting of the continental plate and expansion of the oceanic crust,and has undergone four stages of tectonic evolution,and then the sedimentary filling structure of "lower fault and upper depression" is formed.The Triassic,Middle Jurassic,Upper Jurassic and lower Cretaceous petroleum systems are developed,among which the Triassic and Middle Jurassic petroleum systems are the most favorable.The Bokh Formation with main hydrocarbon source rocks develops dark gray and black gray mudstones with high organic matter content and high degree of evolution.The cen-tral uplift lies between the western and central sags has complete formations and various types of positive structures developed,is an important target of oil and gas migration with good accumulation conditions.We should look for exploration targets around the central uplift based on the petroleum system characteristics in Triassic and Middle Jurassic,and it is the most realistic method of further basin exploration.