Palynofacies, Organic Thermal Maturation and Source Rock Evaluation of Nanka and Ogwashi Formations in Updip Niger Delta Basin, Southeastern Nigeria

The oil and gas prospects in the Nigerian inland basins necessitated the palynofacies characterization, thermal maturation and source rock evaluation of the Nanka and Ogwashi formations of the Niger delta basin. The Nanka Formation has dominant terrestrial microflora, brown structured phytoclasts and amorphous organic matter, opaque debris accompanied by dinoflagellate cysts. The Ogwashi Formation has maximum terrestrial microflora, medium to large brown structured phytoclasts, opaque debris with abundance of dark brown amorphous organic matter and a few marine taxa. Palynofacies constituents of the Nanka Formation reflect Kerogen Type II / III which are Gas / Oil prone shown by abundance of marine species, amorphous organic matter in conjunction with terrestrial phytoclasts and non-marine palynomorphs assemblage. The spore/pollen colour range from light brown to dark brown which suggest oil generation to production of wet gas. This corresponds to thermal alteration index (TAI) 2+ to 3+ and vitrinite reflectance index (%R o ) 0.5% to 1.3%. Palynofacies of the Ogwashi Formation has Kerogen Type III (gas prone) linked with overwhelming abundant terrestrial phytoclasts palynomorphs and large amorphous organic matter of terrestrial origin. Spore/pollen thermal alteration colour ranges from light medium brown to dark brown indicative of mature oil generation and transition to dry gas phase. The thermal alteration index and vitrinite reflectance index (%R o ) values of the Ogwashi Formation is consistent with that of the Nanka Formation.