Comparing the organic matter source input of some Nigerian oils using steranes

Abstract

Molecular geochemical method using Gas Chromatography Mass Spectrometry (GC-MS) was used to access the organic matter source input of the Agbada, Afowo, Yolde and Bima Formation oils. Steranes data obtained reveals that the studied Agbada Formation oil is dominated by terrestrial organic matter source inputs/origin with varying marine and lacustrine influences, thereby receiving a major contribution from terrestrial higher plants. The Afowo, Yolde and Bima Formation oils are dominated by marine organic matter source inputs with varying terrestrial and lacustrine influences, thereby receiving a major contribution from Planktonic and benthic Algae. Ternary plot of the relative amounts of C27, C28, and C29 regular steranes in the studied oils show marked resemblance for oils occurring in the Afowo Formation suggesting the two oils originated from the same petroleum source rock. Steranes of oils occurring in the studied Bima Formation does not match the oils occurring in the studied Yolde Formation. This suggests the possible existence of multiple petroleum systems within the northern Benue Trough. Inferred source rocks for the studied Bima oils is the marine source rocks associated with Bima and Fika Formations. Inferred source rock for the studied Yolde oils is the Marine source rocks associated with Yolde Formation. Inferred source rocks for the studied Afowo oils is the Organic-rich marine shale associated with Afowo and Araromi Formations. Inferred source rocks for the studied Agbada oils is the Organic-rich shales associated with Agbada Formation.