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Petrophysical evaluation of uzek well using well log and core data, Offshore Depobelt, Niger Delta, Nigeria

Adaeze, I. Ulasi; Samuel, O. Onyekuru; and Chukwuma Julian Iwuagwu

Petrophysical well log and core data were integrated in an analysis of the reservoir characteristics of Uzek Well, Offshore Depobelt, Niger Delta Basin, Nigeria. The study essentially determined reservoir properties such as lithology, depositional environments, shale volume porosity (Φ), permeability (K), fluid saturation, net pay thickness, among others from well logs and cores, which are variables that determine reservoir quality. The original hydrocarbon-in-place of each reservoir was also evaluated based on mean weighted averages of porosity, water saturation, gross rock volumes and net-to-gross ratios. The analysis identified four (4) hydrocarbon-bearing reservoirs (I, P, Q, and R). The Uzek Well sandstone reservoirs were generally coarsening upward sequences with gradational/transitional basal and sharp upper contacts reflecting sedimentation in high energy environments, possibly, the shoreface depositional environment. Average permeability values of the reservoirs is above 1000md, while porosity values ranged between 20-30%, reflecting well sorted coarse grained sandstone reservoirs with minimal cementation, indicating very excellent reservoir quality. Fluid types defined in the reservoirs on the basis of neutron/density log signatures were basically water, oil and gas. Low water saturation (12-54) in the reservoirs of the Uzek Well indicated that the proportion of void spaces occupied by water is low, thus, indicating high hydrocarbon saturation. Quantitative porosity verification using Pearson Correlation Coefficient and Regression Equations revealed significant similarity in the porosity values obtained from petrophysical well log and core data. Plots on scatter diagrams using porosity values derived from petrophysical log and that from core analysis for the four reservoirs obtained correlation coefficient (r) values of 0.7165, 0.8094, 0.5835, and 0.5025, respectively for reservoirs I, P, Q, and R, indicating strong linear relationships. Plots of values of water saturation derived from core analysis and that from petrophysical log for the reservoirs also showed linear trends. Plots of porosity values against permeability values showed fairly strong linear relationships between the two variables in all the reservoirs indicating that Uzek Well reservoirs are permeable and have pores that are in strong communication. The petrophysical properties of the reservoirs in Uzek Well are enough to permit hydrocarbon production.