Liquid hydrocarbon source-rock potential of mid-Cretaceous coals and coal measures in the Middle Benue Trough of Nigeria

Abstract

The Middle Benue Trough of Nigeria is filled with approximately 4000 m of Cretaceous sediments. Among these sediments are the Turonian±San-tonian organic matter-rich and coal-bearing strata of the Awgu Formation. Maceral analyses on 32 samples obtained from four boreholes and two outcrop sections from the Awgu Formation allow the subdivision of the coal beds and interseam sediments into three different petrographic/coal facies, namely: a vitrinite± fusinite coal facies, a trimaceritic coal facies, and a shaly coal facies. Vitrinite reflectance (VR) measurements gave values from 0.74 to 1.25% VR. These high VR values in such shallow boreholes arise as a result of the mid-Santonian tectonic episode during which the sediments were folded and faulted, accompanied by uplift. Coalification to the present rank was attained prior to this deformation. All the VR values fall within the zone of oil generation in source rocks. In the study area, however, oil generation potential can be expected only in the trimaceritic coal facies and some parts of the shaly coal facies which are rich in liptinite macerals. The vitrinite±fusinite coal facies with its high content of humic organic matter (vitrinite+inertinite) is likely to generate gas (wet+dry) only, within the given thermal maturity range.

New geochemical data from the Nigerian sector of the Chad basin: implications on hydrocarbon prospectivity

“…This study as well as several previous studies (Petters and Ekweozor, 1982;Whiteman, 1982; Obaje and Abaa, 1996; Olugbemiro et al, 1997;Akande et al, 1998;Obaje and Hamza, 2000) indicate that Nigeria's inland basins, of which the Chad basin is one major part, constitute an extensive stretch of gas shores. With some 160 trillion cubic feet of gas, Nigeria has the 10th largest reserves in the world and second only to Angola on the African continent.…”

Geochemical evaluation of the hydrocarbon prospects of sedimentary basins in Northern Nigeria

“…Increasing evidence, however, suggests that coals and associated type III kerogens can yield not only gas or condensate (e.g., Tissot and Welte, 1984), but also significant quantities of oil (Murchison, 1987;Hunt, 1991;Hendrix et al, 1995). The traditional view that coals are largely gas-prone may be the result of historical bias in the study of North American and European Paleozoic coals, prior to the study of Mesozoic-Cenozoic coals containing contributions from resinous conifers and angiosperms (Obaje and Hamza, 2000).…”

Petrology, Rank And Geochemical Evaluation Of Maastrichtian Coals From Se Nigeria: Implication For Petroleum Generation.

“…14). On a regional scale, the studied coals are suggested to be more prolific than the coals in the Middle Benue Trough, which are essentially gas-prone with some potential for mixed oil-and gas-generation (Obaje and Hamza, 2000). The HI values range from 183.09 to 344.53 mg HC/g TOC, which also indicate the potential to generate mixed oil and gas (Fig.…”

“…Petersen and Nytoft, 2006), the liptinite macerals are more paraffinic in structure and they are likely to be more oil-prone than the huminite. This is favourable for the oil-proneness of the coals, as the oil expulsion efficiency is dependent on the coals' ability to generate long-chain aliphatics (>C [20][21][22][23][24][25] ) (Isaksen et al, 1998). Gas chromatography and gas chromatography-mass spectrometry analyses of the lipid extracts reported biomarkers with a dominance of long-chain n-alkanes (C 24 -C 31 ) with obvious odd-over-even predominance (Fig.…”