Facies analysis and sedimentology of the Campanian-Maastrichtian sediments, southern Bida Basin, Nigeria

The sandstone of the Lokoja and Patti Formations constitutes the main reservoirs of the southern Bida Basin, Nigeria. Detailed facies analysis and diagenesis of these reservoirs intervals in the formations have not received significant investigations. The goal of this study was to apply field observation, facies analysis, sedimentological, scanning electron microscopy (SEM), mineralogical X-ray diffractogram (XRD), X-ray fluorescence spectroscopy (XRF), and thin-section analyses to evaluate the critical reservoir components of the Campanian-Maastrichtian sandstones of the Lokoja and Patti Formations in the basin. The field observations revealed eight lithofacies that were grouped into four affiliations. The grain size revealed that the Lokoja Sandstone is very coarse-fine-grained (0.43-2.70 phi) and moderately poorly sorted (0.50-2.00 phi). The Patti Sandstone facies are coarse-medium-grained and well sorted-poorly sorted (0.35-1.8 phi). The Lokoja and Patti Formation sandstones exhibited skewness ranging from fine to coarse and platykurtic to leptokurtic kurtosis. The results of their petrographic analyses indicate that quartz (48.5-78%) and feldspar (5.24-20%) in the Patti Sandstone predominate those of the Lokoja Sandstones (quartz = 49-68%; felspars = 22-32%) and this indicates that the Patti Sandstones are mineralogical mature than the Lokoja Sandstone. Authigenic kaolinite, chlorite and quartz grains are the main minerals present in the reservoir units. The facies and sedimentological analyses suggested shoreface/foreshore, tidal channels and estuarine delta with fluvial interference. This study has revealed that the sandstones facies from the two units exhibit slightly good potential as hydrocarbon reservoirs in the basin.