Hydrocarbon production potential of paralic reservoirs from the Niger Delta basin: Evidence from ichnological studies

Abstract

Reservoir ichnological study was employed to improve on the inconsistencies and poor interpretation of hydrocarbon-bearing strata within the multipartite maturing terrain of the onshore Niger Delta basin. Ichnofacies characterization revealed two distinctive trace fossil suites that both reflected different feeding behaviours and responses to substrate consistency, which assisted in the high-resolution assessment of facies constituting the paralic reservoirs. Fifteen potential reservoir intervals were subdivided into productive and non-productive as revealed on core slabs as well as well log signatures. Fluctuating river sediment influx has been considered to be detrimental to the colonization of the channel deposits and barrier bars, which resulted in excellent hydrocarbon reservoirs in the study area. The sandstone facies, characterized by sparse bioturbation and extensive bedding, displays imprints of Ophiomorpha, Thalassinoides, and Palaeophycus. The removal of these imprints has minimized subtle heterogeneities, resulting in more uniform reservoir characteristics. This uniformity has favored the accumulation of hydrocarbons within the point bars.Biogenicchurning of bedded sediment generated a poorer sorting index thereby reducing the reservoir quality at 9866-9840ft, 9154-9120ft, and 9090- 060ft depth intervals, which has been interpreted to represent poor reservoir potentials. However, it is advised that future investigations should focus on the forced regressive shoreface and delta front reservoirs of the studied interval for its internal continuity that may contain maximum production potential.