Integrated Geochemical and Organic Petrographic Characterization of the Campano-Maastrichtian Sediments Around Enugu Escarpment, Anambra Basin, Southeastern Nigeria

Grace G. Udofia
Department of Geology, University of Ibadan,Ibadan, Ibadan, Nigeria

The Anambra Basin contains a variety of major hydrocarbon source rocks, such as found in the Post-Santonian Enugu Shales and the Mamu Formation. This study attempts to re-evaluate the discrepancies in past ivestigations based on the prospective value and characterization of the Campano-Maastrichtian source rocks and their hydrocarbon potential taking cognizance of the interactions between source rocks and their prevailing paleodepositional environment.

Fifteen (15) shale and five (5) coal samples collected from outcrops within the study area were subjected to Total Organic Carbon (TOC), Total Sulphur Content (TSC), and Soluble Organic Matter (SOM) analyses. Other standard analysis such as, inorganic geochemical (Major and Trace Element Abundance), Organic Petrographic (Maceral) and granulometric (grainsize) analyses were also carried out.

The TOC contents, 0.65 to 1.82wt% in shale and 18.35 to 19.12wt% in the coal samples, reveal high values. These results exceed the minimum threshold value of 0.5 wt%. Low TSC (0.35 - 0.44) and variable Extractable Organic Matter (EOM) values (998 to 5900ppm) were detected for the representative samples with the higher EOM values detected in the coal samples of the Lower Coal Measures. The source rock evaluation, as deduced from the results indicates good to fair source rock qualities (oil and gas). The TOC values and petrographic count of the maceral analysis show relatively high organic contents in the study area, showing that the hydrocarbon are probably just being generated in the basin and may not have been expelled in large quantities. The depositional environment of these, gas-prone source rocks, indicates an oxic, marine environmental conditions.

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