Organic geochemical and palynological studies of the Maastrichtian source rock intervals in Bida Basin, Nigeria: implications for hydrocarbon prospectivity
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Date
2020-09-02
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Publisher
Journal of Petroleum Exploration and Production Technology (Springer)
Abstract
The Patti Formation which consists of sandstone and shale offers the best potential source beds in the Bida Basin. This inland
basin is one of the basins currently being tested for hydrocarbon prospectivity in Nigeria. Fresh samples of shale from Agbaja
borehole, Ahoko quarry and Geheku road cut were analysed using organic geochemical and palynological techniques to
unravel their age, paleoecology, palynofacies and source bed hydrocarbon potential. Palynological data suggest Maastrichtian
age for the sediments based on the abundance of microfloral assemblage; Retidiporites magdalenensis, Echitriporites
trianguliformis and Buttinia andreevi. Dinocysts belonging to the Spiniferites, Deflandrea and Dinogymnium genera from
some of the analysed intervals are indicative of freshwater swamp and normal sea conditions. Palynological evidence further
suggests mangrove paleovegetation and humid climate. Relatively high total organic carbon TOC (0.77–8.95 wt%) was
obtained for the shales which implies substantial concentration of organic matter in the source beds. Hydrocarbon source rock
potential ranges from 0.19 to 0.70 mgHC/g.rock except for a certain source rock interval in the Agbaja borehole with high
yield of 25.18 mgHC/g.rock. This interval also presents exceptionally high HI of 274 mgHC/g.TOC and moderate amount
of amorphous organic matter. The data suggests that in spite of the favourable organic matter quantity, the thermal maturity
is low as indicated by vitrinite reflectance and Tmax (0.46 to 0.48 Ro% and 413 to 475 °C, respectively). The hydrocarbon
extracts show abundance of odd number alkanes C27–C33, low sterane/hopane ratio and Pr/Ph > 2. We conclude that the
source rocks were terrestrially derived under oxic condition and dominated by type III kerogen. Type II organic matter with
oil and gas potential is a possibility in Agbaja area of Bida Basin. Thermal maturity is low and little, or no hydrocarbon has
been generated from the source rocks.
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Citation
Ojo et al., 2020