Abstract: Baobab structural zone is located in the slope of northeastern Bongor Basin, Central African Rift System. Although it is relatively far away from the basin center, the exploration practice shows that it is the most proliferous area in Bongor Basin. A detailed analysis on structural evolution and controlling factors of hydrocarbon accumulation will provide good reference for petroleum exploration in the Central African Rift System. The structural evolution and oil and gas distribution characteristics in Baobab structural zone are studied to identify the controlling factors of hydrocarbon accumulation. The results show that Baobab structural zone has experienced five main evolution stages,i.e., pre-rift stage, rift stage, depression stage, inversion stage and extinction stage. The deep lacustrine mudstones of the Lower Cretaceous M and P Formations are stably distributed in the rift basin, which are not only the main source rocks, but also good regional caprocks. A series of anticline or fault anticline traps were formed in Baobab structural zone affected by the large-scale structural inversion and strata denudation during the inversion period in the Late Cretaceous, which was conducive to the hydrocarbon accumulation. In the structural highs or bulge areas, buried hill oil reservoirs are developed mainly in bedrock weathering crust and fracture development zone, of which the trap formation, hydrocarbon migration and reservoir transformation are controlled by fault activities. While in subsags close to the bulge area, turbidite channel and fan delta sandstone reservoirs are developed of P Formation, forming oil reservoirs controlled by structure and lithology. As a whole, oil and gas distribution law is characterized by bedrock buried hill oil reservoir in the bulge area, while inside-source P Formation oil reservoir in the subsag area.

Key words: Bongor Basin, Baobab structural zone, bedrock buried hill, structural inversion, hydrocarbon accumulation