Aromatic Hydrocarbon Distribution and Calculation of Oil and Gas Volumes in Post-Santonian Shale and Coal, Anambra Basin, Nigeria
I.M. Akaegbobi, J.I. Nwachukwu, M. Schmitt, 2000. "Aromatic Hydrocarbon Distribution and Calculation of Oil and Gas Volumes in Post-Santonian Shale and Coal, Anambra Basin, Nigeria", Petroleum Systems of South Atlantic Margins, Marcio Rocha Mello, Barry J. Katz
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The generation and distribution of C11+ aromatic hydrocarbons has been investigated in 24 rock samples from the Campanian–Maastrichtian Nkporo shales and coals of the Anambra Basin in the lower Benue Trough. The study focused on dicyclic and tricyclic aromatic hydrocarbons identified on gas chromatograms. The distribution of these compounds and their alkyl homologs are strongly controlled by thermal maturation of organic matter. Compositional variation in the organic macerals as indicated by optical observation seemed to be of minor significance.
A gradual depth trend was observed for compound ratios calculated from the relative variations of the methyl aromatics in each family. The methylphenanthrene index (MPI 1) in particular, as well as other indices derived from dicyclic aromatics, demonstrated a good correlation with maturity. Theoretically calculated vitrinite reflectance values from MPI 1 range from 0.60 to 0.89% Rc. These values are consistent with measured reflectance values (0.61–0.83% Ro) and Tmax values (430–471°C) for type III kerogen within the corresponding depth intervals. These results confirm that the Nkporo Shale and the Lower Coal Measures (Mamu Formation) are mature within the depth range of 1555–2389 m.
Volumetric estimates of the hydrocarbons generated by these shales and coals show that about 779 million bbl of oil or 4.57 × 1013 ft3 of gas may have been generated and probably entrapped in the basin. The basin's low source potential index (4.02) indicates an undercharged system and hence low exploration potential for the basin.
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“Giant oil and gas fields have been discovered through recent exploration in the deep and ultra-deep water regions of Angola, Brazil, and Nigeria. This volume includes 1. Descriptions of the petroleum geology of more than 12 basins along the two margins 2. Discussion of various components of the petroleum systems within these basins 3. Discussion on the use of the petroleum systems concept in the South Atlantic marginal basins to classify and characterize the diversity of the systems 4. Methodologies used in the assessment of petroleum system components 5. Overviews of the different components of the region's petroleum systems. Petroleum explorationists and researchers working in the South Atlantic will welcome this addition to their libraries.
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