Amasiri Sandstone Characterization; Insights from Petrology, Geochemistry and Reservoir Potential Studies

The Amasiri sand stone ridge of the Ezeaku formation was studied for reservoir potentials, and geochemical analysis from which sedimentary features were derived. Field observations show that the sandstones occur in a linear, parallel northeast-southwest trending ridges. Sandstone strata of this group are fine to coarse grained, slightly bioturbated, cross-stratified and rippled bedded which deduce foreshore to superficial marine below wave base. Deductions from petrographic examination indicates the existence of quartz, feldspar, rock remains and muscovite. The computed framework grains suggest feldsparthic (subarkosic) sandstone that is sub matured, the compositional framework grain data plotted in the Craton interior and recycled Orogen arenas. The prediction is thus, that these sandstones under examination results from comparatively low-lying granitoid and gneissic sources, accompanied by sands that are recycled from associated platform or Inert Edge Basins. Data analysis of the geochemical test unvailed that the samples are preferentially enriched with SiO2, TiO2, Al2O3 and Fe2O3 and lessening in K2O, Na2O, MgO and CaO. Chemical Index of Alteration (CIA), Chemical Index of weathering (CIW) and Mineralogical Index of alteration (MIA) calculations show that there was intense weathering at source area, relevant geochemical plots suggest that the sand stone is of none marine origin, deposited in semiarid region (inferring sub mature status) in a passive tectonic continental margin. Reservoir studies shows that porosity ranges from 36.48% – 43.70% with an average of 40.09% while permeability ranges from 1.3945×10-2 – 3.0577×101-2, these values compare satisfactorily with hydrocarbon producing reservoirs in the Nigerian Niger Delta Region and can support hydrocarbon accumulations and production if other elements of petroleum systems are in place.