西南非海岸盆地中生界构造-沉积特征与成藏条件

Mesozoic tectonics-sedimentary characteristics and accumulation conditions in the Southwest African Coastal Basin

西南非海岸盆地位于南大西洋的非洲海岸地区,由上侏罗-下白垩统裂谷盆地和上白垩-全新统被动陆缘盆地叠合形成,是一个热点油气勘探区。在调研国外油气地质研究的基础上,根据地震、测井资料,详细描述了西南非海岸盆地在中生代的构造形态与沉积充填特征,明确了其纵向演化与横向迁移规律,并依据已知油气田的钻井与测试资料,综合分析了盆地油气富集的基本地质条件。研究表明,西南非海岸盆地始形成于侏罗纪晚期,早期以剧烈的断裂与火山活动为特点,裂谷盆地内部填充大量砂岩和页岩;在经历白垩纪巴雷姆期与阿普特期的过渡阶段后,于阿尔布期进入被动陆缘阶段,在过渡与被动陆缘阶段,盆地内部以细粒海相沉积为主,可见少量碳酸盐岩与盐岩。盆地阿普特阶主力烃源岩与其上覆的上白垩统碎屑岩储层共同组成了油气成藏组合。

The Southwest Africa Coastal Basin is located in the African coast of the South Atlantic, which is formed by the superimposition of the Upper Jurassic-Lower Cretaceous rift basin and the upper passive continental margin basin, and is a hot exploration area of oil and gas. In this paper, based on the investigation of foreign petroleum geology, seismic and logging data, the tectonic morphology and sedimentary filling characteristics of the Southwest Africa Coastal Basin during the Mesozoic are described in detail, and the longitudinal evolution and transverse migration are clarified. Combined with the drilling and testing data of known oil and gas fields, the basic geological conditions of oil and gas enrichment in the basin are comprehensively analyzed. The study shows that the Southwest Africa Coastal Basin was formed in the late Jurassic period. In the early stage, the basin was characterized by intense faulting and volcanic activity, and the interior of the rift basin was filled with a large number of sandstones and shales. After the transitional stage of the Cretaceous Barremian Epoch and Aptian Epoch, it entered passive continental margin stage in Albian Epoch. In thermal subsidence and passive continental margin stage, the basin is mainly filled with fine marine facies with a small amount of carbonate and salt rocks.The main source rocks in the basin were formed in the Aptian Epoch, and the overlying clastic reservoirs in the Upper Cretaceous formed oil and gas accumulation assemblages.