Hydrocarbon prospectivity of Nigeria's inland basins: From the viewpoint of organic geochemistry and organic petrology

The inland basins of Nigeria comprise the Anambra basin, the lower, middle, and upper Benue trough, the southeastern sector of the Chad basin, the Mid-Niger (Bida) basin, and the Sokoto basin. Organic geochemical and organic petrologic studies indicate that coal beds constitute major potential source rocks in the whole of the Benue trough (Anambra basin inclusive). The generation and production of liquid and gaseous hydrocarbons from coal beds is presently indisputable worldwide. In the Anambra basin, the coal beds in the Mamu Formation (Campanian–Maastrichtian) have total organic carbon (TOC) contents of as much as 60.8 wt.%, mean hydrogen index (HI) of 364 mg HC/g TOC, vitrinite reflectance (Ro) of 0.54–0.56%, and T max 430–433°C. Biomarker data indicate a dominance of high-molecular-weight n-alkanes, very high pristane/phytane ratios, pronounced odd-over-even predominance (OEP), a preponderance of C29 regular steranes, and relatively high contents of C28. In the middle Benue trough, the coal beds of the Turonian–Coniacian Awgu Formation have TOC contents of as much as 79.1 wt.%, Ro of 0.83–1.07%, and mean HI of 281 mg HC/g TOC, unimodal distributions of both low- and high-molecular-weight n-alkanes with no obvious OEP, a predominance of C29 steranes, and relatively high contents of C27 and C28. Coal beds from the Coniacian–lower Santonian Lamja Formation in the upper Benue trough yielded TOC contents of as much as 50.7 wt.%, with HI of 184 mg HC/g TOC, Ro of 0.70–0.73%, low- and high-molecular-weight n-alkane dominance with an unpronounced OEP, high pristane/phytane ratios, and very high contents of C29 regular steranes. On a basinal evaluation level, incorporating source rock data from the other formations in the respective sectors, plots on the modified Van Krevelen diagram alongside biomarker and maceral data indicate good to fair source rock qualities (oil and gas) in the Anambra basin and middle Benue trough and fair to poor source rock qualities (gaseous to dry) in the upper Benue trough and the Chad basin, with sporadic good to fair source rock qualities in the Lamja Formation (coals) and shales of the Cenomanian–Coniacian Yolde, Dukul, and Pindiga Formations in that part of the Benue trough. Although TOC values and liptinite contents are relatively high in the Mid-Niger (Bida) basin, T max values and biomarker data show that hydrocarbons are probably just being generated in the basin and may not yet have been expelled nor migrated in large quantities. Nuhu is currently a professor of geology at the Nasarawa State University, Keffi, Nigeria (formerly Associate Professor at the Abubakar Tafawa Balewa University, Bauchi, Nigeria). He graduated with B.Sc. and M.Sc. degrees in geology from the Ahmadu Bello University, Zaria, in 1984 and 1987, respectively, and received a Ph.D. in geology from the University of Tuebingen (Germany) in 1994. He held the Royal Society of London postdoctoral fellowship in petroleum geochemistry at the University of Aberdeen, Scotland, in 1997; the German Academic Exchange Service (doctoral and postdoctoral) fellowships in organic petrology and biostratigraphy at the University of Tuebingen in 1990–1994 and 1998; and the Alexander von Humboldt research fellowship in organic geochemistry/organic petrology at the Federal Institute for Geosciences and Natural Resources in Hanover, Germany in 2002–2003. Nuhu also held research tenures with the Exploration Departments of Chevron Nigeria Limited, Lagos (1997–1998), and the Shell Petroleum Development Company of Nigeria Limited in Port Harcourt (2000–2001). He is a member of the Nigerian government's Presidential Committee on Oil and Gas Sector Policy Reform for the National Council on Privatization.Hermann Wehner is the geological director and head of the Organic Geochemistry and Organic Petrology Section at the Federal Institute for Geosciences and Natural Resources in Hanover, Germany. Georg Scheeder, born September 8, 1964, has been working since 1991 in the Organic Geochemistry Section at the Federal Institute for Geosciences and Natural Resources in Hanover, Germany. He obtained the diploma in chemical engineering from the University of Paderborn, Germany, in 1991. He is currently working on his Ph.D. on geochemical investigations of late glacial to Holocene lake sediments in Germany. M. B. Abubakar, born October 3, 1970, is a lecturer at the Abubakar Tafawa Balewa University Bauchi, Nigeria. He obtained a B.Tech. (with honors) degree in applied geology and an M.Sc. degree in sedimentology/petroleum geology from that university in 1995 and 2001, respectively. He is currently working on his Ph.D. on a subject matter that combines organic geochemistry, micropaleontology and sedimentology, and the relationship to the hydrocarbon prospectivity of the upper Benue trough. As a part of Chevron Nigeria Limited's university linkage and community services program, he worked as a well-site geologist in April–May 2000 on Nasara-1 well at Futuk in Bauchi State (Nigeria). M. B. was a recipient of the German Academic Exchange Service scholarship to undertake analyses on some parts of his doctoral project at the University of Tuebingen in Germany (May–August 2003). He is presently the chairman of the Nigerian Mining and Geosciences Society, Bauchi/Gombe Chapter. Aliyu Jauro, born June 27, 1971, is a lecturer in the Department of Chemistry at the Abubakar Tafawa Balewa University (ATBU) Bauchi, Nigeria. He obtained B.Tech. (with honors) and M.Sc. degrees in chemistry from ATBU in 1995 and 2001, respectively. He is currently working on the hydrocarbon potential and technological properties of some Nigerian coal deposits for his Ph.D.