Provenance and tectonic setting of Leuma Field sediments, Coastal Swamp Depobelt, Niger Delta Basin, Nigeria

Geochemical analysis of sediments recovered from NS-1 well and NS-2 well, Leuma Field, Coastal Swamp Depobelt, Niger Delta Basin was done to establish tectonic setting and provenance. Data for ten major elements and forty-three trace elements were obtained from two boreholes. The geochemical signals display systematic  stratigraphic trends in the two wells that depict one source terrain. To determine the provenance of NS-1 well and NS-2 well sediments, Th/Co vs La/Sc plot was utilized which inferred that the sediments from NS-1 and NS-2 wells were derived from felsic source rocks. TiO2 versus Ni bivariate plot was also used to establish the provenance and it revealed that the source of the sediments penetrated by NS-1 and NS-2 wells is predominantly acidic in nature. The provenance of NS-1 and NS-2 wells sediments was further confirmed by considering the ratios of Thorium/Scandium (Th/Sc), Thorium/Cobalt (Th/Co), Chromium/Thorium (Cr/Th) and Lanthanum/Scandium (La/Sc). For NS-1 well, Thorium/Scandium (Th/Sc) range from 1.12-2.01, Thorium/Cobalt (Th/Co) range from 0.91-1.66, Chromium/Thorium (Cr/Th) range from 4.21-16.04 and Lanthanum/Scandium (La/Sc) range from 3.69-8.78. For NS-2 well, Thorium/Scandium (Th/Sc) range from 0.95-2.05, Thorium/Cobalt (Thko/Co) range from 0.94-1.91, Chromium/Thorium (Th/Cr) range from 4.32-15.43 and Lanthanum/Scandium (La/Sc) range from 2.58-6.66. These values inferred that the sediments recovered from NS-1 and NS-2 wells were transported from felsic source rocks.Inorganic geochemical results infer that the tectonic setting for NS-1 and NS-2 wells facies is passive continental margin

Palynological studies of Maastrichtian to paleocene sediments exposed at Okpekpe, western flank of Anambra Basin, Edo State, Nigeria

Outcrop samples were collected at a road cut along Okpekpe road in the western part of the Anambra Basin with a view to establishing the age of the sediments and their depositional environment. These consist mainly of shales, sandstone, siltstone and heterolith. The samples were processed and analyzed using standard palynological procedures. Index fossils of stratigraphic significance were used for dating of the sediments. An extremely poor recovery of palynomorphs characterized by Acrostichum aureum, Laevigatosporites sp, Verrucatosporites sp, Cingulatisporite sornatus, Deltodosporasp, Lycopodium spp, Cyathidites minor, Echitricolporites triangulatus, Retitricolporites irregularis, Retitricolporites sp, Liliacidites sp, Longapertites marginatus, Longapertites sp, Erecipites sp., Monosulcites perspinosus, Retistephanocolpites williamsi, Echiperiporites estalae, Dodoneaviscosa, Echitriporite strianguliformis, Periretipollis spinosus, Marginipollis concinnus, Cupaniedites sp., Gleicheniidites senonicus Andalusiella polymorpha and Andalusiella sp was noticed. A Maastrichtian-Paleocene age and a continental depositional environment were assigned to the sediments.Keywords: Palynology, Anambra Basin, Index fossils, Okpekpe, Mamu Formatio

Shear wave estimation for rock physics reservoir evaluation of jay field in the Niger Delta basin

Shear wave logs are one of the key data required for most Amplitude Versus Offset (AVO) studies and quantitative seismic interpretation. Despite its overwhelming importance, it is hardly available in most wells due to its very high cost of acquisition. In the absence of shear wave logs in the field, the Castagna’s empirical relationship that relates P-wave and S-wave velocities and Biot-Gassman’s Fluid substitution equations were adopted for its estimation. The results obtained revealed that Castagna’s empirical relationship underestimated the Shear wave log in the field, even after Biot-Gassman’s Fluid substitution model was applied to define P-wave of the brine filled scenario. A cross plot of Mu-Rho versus Lambda-Rho presented low values for Mu-Rho due to the underestimated shear wave used. To correct for the underestimation, a modified form of the Castagna’s Equation constants were establish. This was achieved by generating several linear regression equations that defines the relationship between P and S-wave for brine sands in the field. The cross plot of Mu-Rho versus Lambda-Rho done with the modified shear wave gave very good results as expected for both fluid and lithology discrimination. Keywords: Shear Wave, Castagna’s Equation, Biot-Gassman’s Equation, Rock Physics, Cross plot