Assessment of petroleum system elements and migration pattern of Borno (Chad) Basin, northeastern Nigeria

Borno (Chad) Basin is an intra-cratonic rift basin located at the southwestern terminal of the West Africa Rift System. Despite its reported low petroleum potential, oil seepages have recently been found in the basin from its oldest and lowest stratigraphic unit, the Bima Sandstone. The lack of source beds below this reservoir sandstone makes it challenging to classify the basin petroleum system elements (PSEs) in their normal order and to predict the origin of the oil seepages in the region. Coupled structural analysis (2D Move) and petroleum system modeling (PetroMod) were employed to investigate the structural and hydrocarbon evolution of the basin to reassess its PSEs, hydrocarbon potential and migration trends. The structural model shows that the basin has extended up to 2900 km since the Late Cretaceous. The extension controlled by regional tectonic activities has affected the West and Central Africa Rift System and caused some localized tectonic disturbance in the form of igneous underplating and magmatic intrusion, leading to regional uplift. The magmatic sill intruded into the Late Cretaceous source rock formations increased the heat flow for the study area to a peak value of 128 mW/m(2). This anomalous high heat flow value is 38 mW/m 2 above the regional average and 18 mW/m(2) above the average value for a non-volcanic rift margin. Essential petroleum system elements for trapping and accumulation of hydrocarbons were missing as a result of the uplift during the Late Cretaceous, creating hiatus and diverting sediments to other parts of the basin. The PetroMod model result indicates three zones of oil generation: Early Oil, Main Oil, and Late Oil in the Fika Shale and the Gongila source formations. Source rocks became mature at a relatively shallow burial depth of 900 m due to transient heating from the magmatic sill intrusion in the Late Cretaceous. Oil migrated updip to the surface through fault breakouts. The modeling results show no significant entrapment of conventional hydrocarbons in the study area. The findings improve our understanding of the Borno Basin petroleum system setting and offer new insight on the petroleum exploration potential in the region.