Geochemical analysis of Cenozoic Usani sandstone reservoirs, Niger Delta Basin, Nigeria: implications for reservoir quality and petroleum geology.
Publication Date : 23/05/2022
Geochemical (XRD), gamma-ray log, thin section, porosity, and permeability data were integrated to interpreting the depositional environments and evaluate the diagenetic changes, and then assess the reservoir quantity and quality of the wells from the Usani field, Niger delta basin, Nigeria. Gamma-ray log suites and core samples descriptions show that the reservoirs are made up of fine, medium to coarse sandstone lithofacies capped by mudstone and shale lithofacies of different depositional settings ranging from storm dominated shelf, offshore bar to offshore regressive bar depositional environments. The XRD and thin section data show that the dominating mineral is quartz with the presence of feldspar, illite- smectite, siderite, and traces of hematite, pyrites minerals. The high cation exchange capacity values of 8.10 - 8.40meq/100g for reservoirs A, A2, C2, A3, B4, B4 in the wells indicate high clay contents, coupled with the presence of kaolinite, siderite, feldspar, illite-smectite, illite in reservoirs A, A2, C2, A3, B4, B4 at a o depth range of 9400 to 11800ft within a temperature range of 98-110 C in the wells in the field. These characteristics make the sediments of the reservoirs respond faster to diagenetic changes such as compaction and cementation which result in variation in reservoir quantity and quality by reducing the primary porosity of the Usani sandstone reservoirs as the depth of burial increases which contribute to a decline in the quantity of hydrocarbon. The presence of sulphur contents from the pyritic coatings affects the quality of hydrocarbon in terms of worldwide ranking.
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