Petroleum Source Rock Potential of the Upper Benue Trough, Nigeria: Implications for Hydrocarbon Exploration

摘要

Forty six (46) shale samples were collected from borehole, quarry and outcrop in the Northern Benue Trough which consists of Gongola and Yola Basins respectively. The Gongola Basin comprises Bima Formation, the Yolde Formation, Pindiga/Gongila Formation and capped with Gombe Formation whereas the Yola Bain consists of Bima Formation, Yolde Formation, Dukul/Jessu/Numanha Formation and capped with Lamja Formation. The samples were subjected to vitrinite reflectance, Rock Eval pyrolysis and infrared spectroscopy in order to evaluate their organic richness, thermal maturity and petroleum generating potential. The total organic carbon (TOC) values of the Gongola Basin are between 0.20 and 2.46 wt. % averaging 0.70 wt. % while that of Yola Basin range from 0.11 to 12.9 wt. % averaging 1.50 wt. %. The mean random vitrinite reflectance (Rom) values in the Gongola Basin range from 0.48% in the Gombe Formation to 0.65% in the Pindiga Formation and 0.67% in the Gongila Formation. Also, the reflectance values in the Yola Basin increase with stratigraphic age ranging from 0.63 to 0.80% in the Dukul and Yolde Formations respectively. The thermal maturity of the organic matter (T_(max)) values from the pyrolysis of shales in the Gongola Basin is between 420 and 440°C while that of Yola Basin range from 435 to 445°C. The plot of hydrogen index (HI) vs T_(max) for classification of kerogen in the Gongila and Pindiga Formations reveals prevalence of Type III kerogen while that of Dukul and Yolde Formations shows Type II – III kerogen. The results obtained suggest that Gongola Basin source rocks are fair and thermally immature to marginally mature and have potential to generate gas in the deeply buried section whereas the Yola Basin source rock are between fair to good and thermally mature with potential to generate oil and gas in the deeper section.