东非裂谷系西支构造样式及其对油气成藏的控制作用

The tectonic style of the west branch and its control action to hydrocarbon accumulation in the East African Rift System

基于东非裂谷系西支地震地质综合解释对比研究，发现该生长型裂谷盆地受基底属性影响，主要发育陡断面地堑型盆地结构，沿边界主控断裂走向发育背离型和接近型两类主要调节构造，沿边界主控断裂倾向主要发育地垒式和地堑式两类调节构造。构造样式控制了主要成藏条件：陡断面地堑式裂谷能够形成沉积范围广、厚度大的湖相优质烃源岩；裂谷间走向调节构造属于一级调节带，控制长轴辫状河三角洲的展布；裂谷内错断的边界断裂带属于次级走向调节构造，控制中小型扇三角州的发育。倾向调节构造形成的断鼻、断块圈闭，为该类盆地的主要油气藏类型。

Integrated seismic interpretation and geological study on the west branch of the East African Rift System demonstrate that the growing rift basin is controlled by the properties of basin＇s basement. So that, the high-angle graben is developed in the rift system. Divergent and convergent accommodation structures are developed along the trend of the system. Horst and graben are the main accommodation structures in the dipping direction of the main faults. Tectonics and structures controlled the main petroleum conditions： High-angle graben rift can form extensive and thick lacustrine sediments containing high-quality hydrocarbon source rock; inter-rift accommodation structure is the first-class accommodation belt which controls the distribution of the braided river delta; intra-rift broken boundary faulting zone belongs to secondary strike accommodation structure which controls the development of small-and medium-sized fan delta. Faulted nose and block traps controlled by the accommodation structure along the fault dipping direction are the primary reservoirs in this type of basin.