The release of petroleum from Central Africa rift basins over geological time as deduced from petroleum systems modelling

The Cretaceous basins within the Central Africa Rift sub-system (CAS) share similar tectonic processes, histories, and styles of basin fill, raising the question of the extent to which oil and gas generation is synchronised across the West and Central African Rift System (WCARS). Basin modelling was used to calculate the amount of hydrocarbons generated, the development of sealing capacity and losses of petroleum to the surface for the Melut, Fula, Sufyan, Bagarra, Doseo, and Doba rift basins. It was found that critical periods of hydrocarbon generation within the CAS occurred in the Lower Cretaceous, Upper Cretaceous and Paleocene-Eocene. During the Lower Cretaceous, regional seals had yet to be deposited, while during the Upper Cretaceous and Paleocene-Eocene, seals were poorly compacted and likely still did not constitute a good seal. During these intervals of time, high volumes of petroleum left the petroleum system (e.g. seeped to the surface). The resultant rates of methane seepage for the CAS rift-basins was 10¹–10⁵ tons/year and is both quantitatively significant, and comparable to similar basins and rift systems. This rate of seepage is sufficiently high as to imply that micro-seepage alone would not have been capable of releasing the methane and that at least some seepage would have been catastrophic.