关键词: 被动大陆边缘, 深水, 东非, 大气田, 坦桑尼亚盆地, 鲁伍马盆地

Abstract: In recent years, the deep-water area in the passive continental margin has become a hotspot of global petroleum exploration, and the large-scale new oil and gas fields are mostly discovered in sea area, especially the deep-water area. Therefore, a unified analysis of tectonic evolution and sediments filling of a group of basins at the same continental margin, and the geological characteristics study of the discovered oil and gas fields, as well as the defined hydrocarbon accumulation conditions and patterns will provide important guidance to screen regional-level favorable oil and gas plays and acquire new projects. By using oil and gas field data base, such as IHS and Wood Mackenzie, and integrating with the new discoveries and internal evaluation data of new venture projects, the geological settings and hydrocarbon accumulation conditions of nine basins in the deep-water area in East Africa are systematically analyzed, and the favorable oil and gas plays in deep-water area are proposed. The study results show that the basin group in East African sea area experienced three stages of tectonic evolution, i.e., Karoo rift in the Early Carboniferous-Triassic, Madagascar rift in the Jurassic, and passive continental margin since the Cretaceous. Jointly controlled by transfer faults in the Indian Ocean, extensional fault system at the continental margin, and fault system in the East African rift system, the basement faults are divided into four tectonic segments from north to south, and significantly different section structure and sediment filling characteristics show in various basin segments. Three sets of source rocks were developed in East African sea area, including the Lower Jurassic, Middle-Upper Jurassic to Cretaceous and Paleogene. Two types of superior reservoirs of marine turbidite sandstone and delta sandstone were deposited, which formed a good reservoir and cap rock assemblage associated with the regional massive marine shale. Three sets of deep-water hydrocarbon accumulation assemblages are identified, including two proven assemblages in the Cenozoic and Cretaceous, as well as the inferred assemblage in the Upper Permian-Jurassic. Three types of deep-water hydrocarbon accumulation patterns are established: (1) hydrocarbon generation and supply in the early-middle stage of drift period and hydrocarbon accumulation during the drift period; (2) hydrocarbon generation and supply during the rift period and early stage of drift period, and hydrocarbon accumulation in the riftdrift period; (3) hydrocarbon generation and supply in the rift period, and hydrocarbon accumulation in the drift period. Two types of deepwater fan bodies were formed in the passive continental margin period in East African sea area, namely the fan complex mixed by the largescale delta and deep-water gravity flow sediments, and the nearshore superimposed small fan lobes dominated by slumping and without any material supply from the large-scale paleo rivers. The Paleogene favorable deep-water oil and gas plays have certain inheritance to those of the Cretaceous, which are mainly developed in the southern Tanzania Basin and the northern Rovuma Basin, and the exploration targets are dominated by natural gas and clastic rocks.