Geochemical and Palynological Studies of Some Maastrichtian Source Rock Intervals (Patti and Gombe Formations) in Nigeria: Implications for Hydrocarbon Prospectivity
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Date
2019-01-14
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Publisher
American Association of Petroleum Geologist (AAPG)
Abstract
The Maastrichtian Patti and Gombe Formations are located in Bida and Gongola Basins respectively. These two inland basins form part of the
targets currently being tested for hydrocarbon prospectivity in Nigeria. Road cuttings and core samples of coal, coaly shale, and shale from the
formations were analyzed using standard organic geochemical and palynological techniques to unravel their organic matter quantity, quality,
palynofacies, expulsion efficiency, and thermal history. The age of the sediments were also constrained from the palynological data.
Palynological data suggest a Maastrichtian age and influence of freshwater swamps for the sediments based on the microfloral assemblage like
Retidiporites magdalenensis, Echitriporites trianguliformis, Buttinia andreevi, and Botrycoccus braunii. The organic geochemical results show
relatively high TOC for the Patti shales (0.79-12.9 wt.%) and Gombe coals (38.8-61.2 wt.%) implying moderate to high concentrations of
organic matter. Hydrocarbon source potential range from 0.19-0.70 mgHC/g rock except for a certain interval with high yield (30.23 mgHC/g
rock) in the Patti shales. The Gombe coals have source potential ranging from 32.77-69.38 mgHC/g rock. Generally, the samples show low HI
except one of the Patti shale samples with HI of 230 mgHC/g TOC (thought to be formed under reducing condition) and one of the Gombe coal
samples with HI of 170 mgHC/g TOC. In spite of the favorable organic parameters, the thermal maturity is low with vitrinite reflectance and
Tmax ranging between 0.41-0.52 % and 413-431 °C respectively. Biomarker analysis of the hydrocarbon extracts show abundance of odd
number alkanes C27-C33, low sterane/hopane ratio (0.06-0.25). Pr/Ph in the samples are greater than 2. We conclude from the study that the
Maastrichtian source rocks were sourced terrestrially under a prevailing oxic condition and dominated by Type III organic matter. Type II
organic matter with oil and gas potential may be possible in the Patti Formation in the Agbaja area of Bida Basin. Thermal maturity and
conversion ratio were low and not much hydrocarbon could have been generated from the source rocks.
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Citation
Ojo et al., 2019