Abstract:

Based on predecessors achievements and petroleum exploration data from new findings, this paper analyzes the geological characteristics and deepwater hydrocarbon accumulation patterns of the transformed passive continental margin basins in the Equatorial West Africa, which are controlled intensely by transform fault. According to the structural interpretation and stratigraphic analysis, it can be seen that the basin shape, basement faults, deformation sequence and regional stress are all controlled by this transform fault. These basins have undergone four phases of evolution: the intracontinental sedimentary phase during pretransforming, the intracontinental sheared phase during rifting, the continentocean transform phase during transpression and the passive marginal phase during thermal subsidence. Four regional unconformity faces that migrated from east to west were formed. Three different sedimentary sequences were filled, including lacustrine clastic rocks in the intracontinental sheared stage, mainly clastic rocks of continental and littoralneritic facies in the continentocean transform stage, and mainly clastic rocks of marine facies in passive marginal stage. Some geological structural characteristics, such as narrow continental shelf, steep continental slope and high angle transtensional fractures, revealed that the transformedridge or platform could be easily developed. Generally, small sources migrated short distances and accumulated quickly near coasts in deepwater areas, forming sandrich small fans or fan complexes which were superposed vertically and showed apronstyle in lateral. Deepwater petroleum exploration should focus on stratalithological and anticlinal structural traps in continentocean transform stage and early passive marginal stage.

Key words: transform type, rifted type, passive continental margin, deepwater, West Africa, Equatorial Atlantic, transform fault