Hydrocarbon prospectivity of the southern Bida and northern Anambra basins, Nigeria using palynological and geochemical studies

Abstract

• Hydrocarbon prospectivity and depositional environments of two basins. • Integrating palynological and geochemical data in evaluating hydrocarbon potential. • Identifying the depositional environments of the basins. The palynological and geochemical analyses were carried out on shales samples in borehole and outcrop sections of the southern Bida and northern Anambra basins respectively. These analyses aimed at evaluating the hydrocarbon prospectivity of the basins. The results of total organic carbon (TOC) of 0.30–9.01 wt% in Patti Shale interval of Agbaja section in southern Bida Basin revealed a high TOC, depicting a substantial organic matter in the source rock. TOC of 0.82–2.56 wt% for Patti Shale in Ahoko outcrops (southern Bida Basin) show relatively moderate TOC which revealed a fair organic matter in the source beds. TOC of 0.44–0.95 wt% of Mamu Shales in Ojodu outcrops in northern Anambra Basin indicates a moderate to poor TOC which suggests fair to poor organic matter in the source rock. Hydrogen Index (HI) range of 45- 153 mgHC/grock with producible hydrocarbon (S 2 ) of 2.60–5.00 mgHC/grock reveals very good source rock potentials in the Agbaja section. HI of 0.08–0.57 mgHC/grock, S 2 of 0.12 mgHC/grock in Ahoko and HI of Mamu Shales of 30–136 mgHC/grock, S 2 of 0.14–0.90 mgHC/grock in Ojodu outcrop, both revealed poor to fair source rock potentials. The results of vitrinite reflectance (Ro) and maximum temperature (T max ) range (0.30 to 0.55% and 420 to 435 °C, respectively) suggest a low to relatively high thermal maturity index in both frontier basins. The thermal maturity of the shales in Agbaja borehole sections is moderate to high, although from record no petroleum has been produced from the sections in the basin. From the organic matter type, the kerogen is classified as type II/III and IV for both basins. The palynological results propose the Maastrichtian age for both basins, regarding the rich accumulation concerning micro-florals; Psilatricolporites prolatus, Florentinia laciniata seghiris, Echitriporite trianguliformis, Arecipites sp. Monoporite, Triporites . Dinocysts belonging to the Spiniferites, and Deflandreacean dinoflagellate, and Acritaarchs of Polipodiaceosporite retigularis, Acripite sp., which were analyzed from the shale intervals in the basins; suggest a Cretaceous age, marginal marine-continental environments, paleovegetation, and humid climate. Finally, the palynological, and geochemical analysis results will contribute knowledge that will be useful for hydrocarbons exploration in these frontier basins in Nigeria.