Impact of Texture and Diagenesis on Reservoir Quality of Some Pre-Santonian Sandstones (Asu River Group and Eze-Aku Formation), Southern Benue Trough, Nigeria

This research presents a detailed study of the pre-Santonian sandstones of the Asu River Group and the Eze-Aku Formation exposed in southeastern Nigeria. Intensive field studies complimented with laboratory thin section petrography, X-ray diffraction (XRD), porosity and permeability studies were carried out to determine the main controls on reservoir properties of these sandstones. Results revealed that the reservoir rocks within the study area consist of consolidated, poorly to moderately sorted, very fine–coarse grained arkosic arenites deposited in shallow to deep marine settings, associate with other non-reservoir lithologies (e.g. siltstones and shale). The porosity in the studied reservoir sediments was determined petrographically and ranged from 3.00 – 6.00; the permeability values determined from the porosity vs grain size plot range from (0.3mD – 3.5mD). X-ray diffractometry revealed that the following clay minerals constituted the major phase in the cementation of the sandstones viz kaolinite, mixed layer kaolinites (nacrite, dickite, halloysite, chrysotile, lizardite), illite, chlorite (corrensite) some silicates, carbonates and sulphate mineral groups. Compaction, cementation (carbonate, clay silica) bioturbations and dissolution of unstable framework grains are the principal diagenetic processes responsible for the modification of the reservoir quality of the sandstones in the study area.