Sedimentary facies and textural characteristics of Cretaceous sandstones in the southern Bida Basin, Nigeria: Implication for reservoir potential and depositional environment

Abstract

A study of sedimentary facies, mineral and textural characteristics of sections of conglomerates/pebbles and sandstone facies found within the Lokoja and Patti Formations in southern Bida Basin, Nigeria, is carried out to evaluate the paleo-environment and reservoir quality of the sandstones of the formations through field observations and textural and mineralogical (using X-Ray Diffractogram) analyses. Nine lithofacies are identified and grouped into three main facies associations. These sedimentary facies suggest deposition in both foreshore and estuaries. The mineral analysis (XRD) shows that the quartz content in sandstone facies of the Lokoja Formation ranges between 49% and 67%, and that of the Patti Sandstone between 43% and 56%, indicating a quartz dominance. The granulometric studies reveal that the Lokoja Formation comprises coarse-to medium-grained (−0.63 to 1.30 φ) sandstone with moderate-poor sorting of 0.72–1.82 φ. On the other hand, medium to fine-grained sandstones dominate the Patti Formation, which is averagely poorly sorted (1.29–1.54 φ). The sandstones are coarsely skewed to finely skewed, with the kurtosis ranging from very platykurtic to leptokurtic. Morphological results of the pebbles from both Lokoja and Patti Formations indicate that the study areas are mainly characterized by the interplay of both wave and fluvial processes, which suggests that the environment of deposition of sandstone facies is predominantly of the fluvial to the shallow marine environment with the indication of tidal influence.Integrating sedimentary facies and textural results suggests subtidal sand ridge/foreshore, estuarine mudflat, and estuarine delta environments with fluvial influences. Evidence from the textural and mineral characteristics indicate that the sandstone facies of the Lokoja and Patti Formations are fairly matured and can act as potential hydrocarbon reservoirs in the formations. The facies, XRD mineral, and textural results have revealed potential hydrocarbon reservoir areas and paleo-depositional features of the Lokoja and Patti Formations.