Geochemical Appraisal of the Mamu Shales Exposed around Igodor in the Benin Flank of the Anambra Basin, Nigeria

The Auchi area of Edo state which lies within the Benin flank of the Anambra Basin host shaly sediment exposures that have been classified by  previous researches as units of the Mamu Formation. This study evaluated samples of this sediment from Igodor near Auchi for its geochemical and  mineralogical properties, and intereted its, depositional environment and geotectonic setting. In order to achieve this, field studies were  carried out and representative samples obtained for Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) analyses of major oxides, trace and rare earth elements. X-Ray Diffraction analysis was also carried out to determine the mineralogical composition. Some of the minerals determined were Aragonite and galena. Binary plots, triplots and elemental ratio plots including SiO2/, Al2O3, Th/Sc, Th/Co and La/Sc , Th-Sc-Zr, and the abundance of Cr, Ni were employed to determine the provenance. The concentration of detrital indicators such as SiO2, Al2O3 and TiO2, with averages of 51.95, 25.34 and 1.39 respectively, indicate high detrital influx into the Benin Flank of the Anambra basin. SiO2/Al2O3 ratios of 1.80-2.20, indicate that the shales were made up of pure kaolinite. The Ni and Cr abundance indicated a mafic and felsic provenance for the sediments, however, Th/Sc, Th/Co and La/Sc ratios show that the provenance was predominantly felsic, while the Th-Sc-Zr triplot shows that the depositional setting was passive

Petrophysical evaluation of reservoir in a selected well (Z) in an onshore oil field (X) in the Niger Delta Basin, Nigeria using wireline logs

: The petrophysical properties of a well selected from among the onshore oil fields in the Niger Delta Basin, Nigeria was evaluated using gamma ray log, resistivity log and neutron-density overlay log to analyze for the hydrocarbon potential of the well. Some petrophysical properties of the reservoir rocks and fluid characters such as porosity, shale volume, effective porosity, permeability, and formation resistivity factor, resistivity of water, hydrocarbon saturation, water saturation, and net pay thickness were evaluated. The results show that the volume of shale in each reservoir zone directly affects the effective porosity and the zones. The volume of shale is inversely proportional to the effective porosity, as an increase in the volume of shale will bring about a decrease in effective porosity. On the other hand, permeability is dependent on the effective porosity. Facies type identification of the reservoir sands were also carried out using the wireline log - Gamma Ray Log. Results of the work revealed the presence of hydrocarbon in 10 reservoirs across the well, and the hydrocarbon type was observed to be only oil. Oil/Water contacts occurred at 2288m, 2518mm, and 2989m, and the Net Pay Thickness was calculated to be 238m, that is the total thickness of the hydrocarbon reservoirs.Keywords: Petrophysics, Wireline logs, Facies, Reservoir rocks, Pay thickness

Geochemical and sedimentological characteristics of the late quaternary sediments of the Anambra Basin

Ten samples from sand bars, mouth bars and continental shelf at the Onitsha end of the River Niger were analyzed for their sedimentlogical and geochemical characteristics. The textural analysis carried out on the samples revealed that they ranged from fine to medium grained, moderately to poorly sorted, angular to sub-rounded. The percentage of sand is high compared to that of silt and clay which has a small percentage. Geochemical analysis shows that the samples are high in silica (SiO2) content, and due to the poorly sorted nature of the sediments, they were described as immature. The mean grain size ranges from 0.8 to 2.9, which corresponds to coarse-fine grain sands but averagely 2.03, which is fine grained. Standard deviation ranges from 0.28 to 1.2, which range from well sorted to poorly sorted but averagely 0.74, which is moderately sorted. The skewness ranges from -0.34 to 1.13 i.e. strongly coarse skewed to strongly fine skewed but averagely near symmetrical. The kurtosis ranges from 0.42 to 1.25 i.e. very platykurtic to leptokurtic but averagely 1.4 which is leptokurtic. The comparison between the samples(sand bar, mouth and continental shelf sediments) revealed certain distinguishing characteristics; the sand bars are better sorted compared to the continental sediments, they are also of fine grain sands, intensive weathering and texturally more mature compared to the continental shelf sediments, whereas the continental shelf is characterized by poor sorting, medium and coarse grains The mouth bar has similar characteristics with the continental shelf with grain size ranging from fine to coarse grained sands.Keywords: Sedimentological, Geochemical, grain size, skewness, kurtosi

Use of Sedimentological and Geochemical Parameters to Evaluate the Lithologies and Geochemical (Na/Zn and K/Mn) Ratios of OGE-1 Well, Niger Delta Basin

This work focuses on subjecting ninety (90) sidewall core well samples to sedimentological and geochemical parameters to determine the lithologies and the geochemical ratios of the OGE-1 Well in the Niger Delta Basin. The sedimentological analysis with sample description yielded lithologies that are sand, shaly sand, sandy shale and shale. The sand lithologies ranged from fine to coarse grained, well sorted to poor sorted at different depths, while the shale lithologies ranged from light to dark coloured shales which is controlled by the organic matter content in the shale. This finally produced a lithologic frame work of the well. The result of the geochemical analysis led to the creation of the geochemical ratio of Na/Zn (0.739 – 5.610) and K/Mn (21.170 – 69.37) for 90 side wall core samples. Na and K had variations in their graphs showing intermittent alternating abundance downhole. Na and K being components of the weathering of feldspars are indicative of abundance of clay minerals. The variation ofthe Na/Zn and K/Mn profile indicates the alternate deposition of clay and sand size deposits giving the environment of deposition to be paralic. Keywords: Chemo-stratigraphy, Paleo-environment, Sedimentological, Stratigraphy, Geochemistr