东非鲁伍马盆地深水区构造-沉积演化过程及油气地质特征

Tectonic-Sedimentary Evolution and Petroleum Geology Characteristics in Deepwater Area in Rovuma Basin,East Africa

利用深水区的二维、三维地震资料开展构造-沉积演化研究,鲁伍马盆地二叠纪—早侏罗世为冈瓦纳陆内—陆间裂谷活动期,发育河流—湖泊沉积;中侏罗世—早白垩世为马达加斯加漂移期,位于剪切型大陆边缘,发育海陆过渡相沉积;晚白垩世—渐新世为被动大陆边缘期,深水沉积广泛发育,重力流沉积延伸至戴维隆起带;中新世—第四纪为东非裂谷海域分支活动期,陆坡和凯瑞巴斯地堑发育深水重力流沉积。盆地垂向上形成"断—坳—断"结构,二叠纪—早侏罗世及中新世—现今发育两期明显的裂谷活动。马达加斯加漂移期的海相泥岩为深水区的主力烃源岩,古近纪的陆坡深水浊积砂体为主要储层。东非裂谷海域分支的断层活动沟通了下伏烃源岩,晚期断层不发育的西部陆坡成为主要的油气聚集区。

According to the 2D and 3D seismic data from the deepwater area, it is interpreted that several stages of tectonic-sedimentary evolution have undergone in Rovuma Basin. Fluvial and lacustrine sedimentary environments developed during Permian to Early Jurassic Gondwana intracontinental-intercontinental rifting. Marine-continental transitional sedimentary environment developed during Middle Jurassic to Early Cretaceous Madagascar drifting. Deep-water gravity flow deposits widely developed in the slope, and extended to Davie Ridge, during Late Cretaceous to Oligocene passive continental margin stage. Deep-water gravity flow and abyssal argillaceous deposits developed in both the slope and Kerimbas Graben during Miocene to Quaternary faulting of the East African Rift System Sea Branch. A“fault-depression-fault” structure pattern that formed in vertical in the basin just brought from the important Permian-Early Jurassic and Miocene-Quaternary riftings. The marine mudstone deposited during Madagascar drifting is the chief source rock and the Paleogene deepwater turbidite sand body in the slope acts as the main reservoirs. The faulting of East African Rift System connects the underlying source rocks with Paleogene reservoirs in the western slope, thus oil and gas accumulate generally in the western slope where faults have hardly developed late.