Tar sand occurrence: Implications on hydrocarbon exploration in the offshore Benin Basin

The Benin Basin, just like other marginal basins in the Gulf of Guinea, evolved in the Cretaceous following the opening of the Atlantic. These other basins have recorded significant oil and gas discoveries offshore unlike the Benin Basin that has records of only large tar sand deposits onshore. A review of key play elements of the basin is carried out to assess the possible occurrence of oil and gas in its offshore part. The basin holds a high prospect for both oil and gas in the offshore with the oil kitchens probably occurring within the lower to upper Cretaceous sediments. Besides containing shales deposited during the world-wide Turonian anoxic event that could serve as source rock, the Turonian sequences also have shelf to slope deposits, which are likely to be turbidite of deep-water environments. These turbidites could serve as an excellent reservoir in the basin. Several thick shale sequences within the Cretaceous to Tertiary could provide enough seal for hydrocarbons. In addition, unconformity surfaces marked by reflection terminations that are very significant during pre-drift and syn-rift tectono-stratigraphic development of the basin point to existence of stratigraphic traps in the basin. Concentration of these petroleum elements within the Cretaceous sequences suggest that exploration efforts should be geared toward the Cretaceous, particularly the Turonian sequences in the basin.