| The basins along the middle sector of East Africa along the Indian Ocean are typical passive margin basins with a huge exploration potential for oil and gas resources.This sector is one of the hot spots for current oil and gas exploration in the world.With public literatures,IHS commercial data and previous research results as the data base,this study applied the theories of basin analysis and petroleum geology to investigate the basic geological characteristics and petroleum geological features of passive margin basins in the study area,make a systematic comparison of the geological features in different basins,document oil and gas distribution patterns and determine the main factors controlling differential hydrocarbon enrichment.The results show that:(1)the passive margin basins have experienced four stages of tectonic evolution,which are pre-rift,syn-rift,early passive margin and late passive margin.(2)The oil and gas discoveries are dominated by giant and medium-large sized oil and gas fields,and the hydrocarbon enrichment is characterized by "less at both ends and more in the middle".The discovered oil and gas reserves are concentrated in the Rovuma Delta domain in the central part of the Rovuma Basin and the Mafia deep water sub-basin in the Tanzania Basin,which host 73.66% and12.17% of the discovered oil and gas reserves in the study area respectively.Stratigraphically,they are mainly confined to Cretaceous to Neogene reservoirs deposited in the passive margin stages.(3)Hydrocarbon enrichment is mainly controlled by high quality Jurassic source rocks deposited in the restricted marine environment during the syn-rift stage and initial phase of the early passive margin stage,Cretaceous-Neogene deep water high-quality sandstone reservoirs deposited during the late passive margin stage,and fault migration pathways.The development of large-scale reservoirs was constrained by the large fluvial delta-deep water gravity flow depositional systems. |
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