Assessment of Reservoir Qualities of The Yolde Formation Along Pantami Stream Channel, Gongola Sub- Basin, Northern Benue Trough, Ne Nigeria

Abstract

The Yolde Formation conformably overlies the Bima Sandstone. It is Cenomanian in
age and marks the onset of marine transgression into the Gongola sub basin of the
Benue Trough. Comprises mainly of sandstones, limestone, shales, clays and
claystones. The study section exposed about 70m thick of the Yolde Formation along
Pantami stream channel, Gombe, Gombe town. Several lithofacies of sandstones
and mudstones ware identified. The sandstones vary from very fine, fine, medium
to coarse grained. Sedimentary structures identified include parallel, planar cross-
beddings, trough cross-beddings and herringbone cross-stratification. Lithofacies
analysis shows series of fining and coarsening upward sequences which indicate
increase and decrease in depositional energies within the environment.
Petrographic analysis shows that the sandstone samples are texturally matured.
The Quartz grains are both monocrystalline and polycrystalline in nature while the
sub-rounded to rounded nature of the grains suggests that the sediments were
transported from a long distance. The framework components of the sandstones
based on the QFR plot shows that the sandstones are Quartzarenite, Sublitharenite
to Litharenite and Subarkorse to Arkosic in nature. Grainulometric analysis shows
that the sandstones are moderately to poorly sorted (1.0-2.0)∂I, the grains sizes are
fine to medium (2.7-0.9)MZ platykurtic to very leptokurtic (0.9-1.9)KG and are
coarse to strongly fine skewed (0.04-0.6)SKI. From the histograms, the sediments
are generally unimodal indicating the same sources of sediments, typical of fluvial
environment. Also, the poor sorting and fine skewness is as a result of increase and
decrease in depositional energies by river/wave processes which was further
buttressed by bivariate plots. Porosity of the samples assessed indicate moderate
to good porosity and the permeability assessment indicate moderate to good
permeability as well.