The sediments of Sahaiawei-1 Well in the Northern Delta Depobelt are represented by sand and shale alternation. Lithofacies characterization and X-ray diffraction technique were used to characterize the sediments from the well in order to characterize the lithofacies, identify the minerals present, determine environment of deposition and identify potential zones for hydrocarbon exploitation. The lithofacies characterization was based on the textural properties, mineralogical composition, fossil content, homogeneity and heterogeneity of the lithofacies units of the well. The lithofacies analysis for Sahaiawei-1 Well identified four (4) lithofacies types of mainly sandstone, shaly sandstone, sandy shale and shale; and fourteen (14) lithofacies zones. The result of the X-ray diffraction analysis identified the following clay minerals – kaolinite, illite/muscovite, chlorite and sepiolite; carbonates and non-clay minerals. Therefore, due to the high percentage of kaolinite in Sahaiawei-1 Well (2% to 39.87%), it could be concluded that pore filing kaolinite may have more effect on the reservoir quality than the pore bridging illite and pore lining chlorite.
Keywords: alternation, lithofacies, X-ray diffraction, reservoir, mineralogy
Geochemical analysis of sediments from Sahaiawei-1 Well of the Northern Delta Depobelt in the Niger Delta Basin was carried out to classify the sediments, determine the provenance, tectonic setting and depositional environment. Twenty (20) ditch cutting samples between 1500 and 10730 ft. were subjected to X-ray fluorescence analysis to determine the elemental composition. The result for the classification of the sediments shows that the sediments were classified as Fe-shale and Fe-sand. The discriminant function diagrams for provenance signature and tectonic setting show that the sediments were plotted within the quartzose sedimentary provenance and passive continental margin tectonic setting fields respectively. The depositional environment using inorganic geochemistry shows that the sediments were deposited with in the continental, transitional and marine environments. This research has provided up to date information on the geochemistry of the Northern Delta Depobelt which would help in hydrocarbon exploration in the area.
Studies were carried out on fresh samples of sandstones from parts of the Bima Sandstone to classify it on the basis of its textural and compositional characteristics. Grain size analysis of samples reveals that they are fine to coarse-grained, moderately sorted to poorly sorted, coarse skewed to strongly fine skewed and very platykurtic to extremely leptokurtic. Thin-section analysis reveals the sandstones to be lithic subarkoses, subarkoses, and lithic arkoses comprising averagely of 66.6% quartz, 21% feldspar and 12.4% rock fragments. The appreciable amount of feldspar, the dominance of subangular to angular grain shape and the poorly sorted nature of the sandstones suggest that they are texturally and mineralogically immature sediments. Bivariate plots of graphic mean versus standard deviation, skewness versus standard deviation and simple sorting versus simple skewness indicates a fluvial origin for sandstones deposited under a moderate to high energy level.
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