Kerogen characterisation and petroleum potential of the Late Cretaceous sediments, Chad (Bornu) Basin, northeastern Nigeria

Detailed microscopic observations (palynofacies) and organic geochemical analyses were conducted on insoluble sedimentary organic matter (kerogens) from the Late Cretaceous sediments in the Chad (Bornu) Basin, northeastern Nigeria. This is to assess their origin, paleoenvironment and types, as well as their petroleum potential. The organic matter is mainly composed of mixed terrestrial plant and marine algae-derived AOMs. Phytoclasts are also present in significant amount in most of the samples, especially those obtained from the upper section of Fika Formation. However, most of the AOMs appears to be degraded and were not well preserved. The variations of relative abundances of marine and terrigenous organic matter may be controlled by terrestrial input in ocean and/or preservation rather than marine production. This organic matter was likely deposited in marine environment under environmental conditions that were mostly dysoxic. The intense degradation observed in most of the organic matter may be as a result of high thermal maturity. Further evidences in this study confirmed that most of the potential source rocks in Chad (Bornu) Basin contain Type III kerogens, but Type III/II kerogens were also present in some parts of the basin, especially at the upper section of Fika Formation. It was also revealed that most of the samples, especially those at the deeper sections of the basin display high aromatic character which suggest a dominant gas-prone nature of the organic matter. This study confirmed that a potential for gas generation exist in this basin.