Elastic Property Variations of Hydrocarbon-Bearing Sandstones in Uzondu Field, Niger Delta Basin, Nigeria

Abstract

Comprehensive reservoir characterization requires integration of petrophysical evaluation and elastic property analysis to understand both storage capacity and seismic response. Therefore, the objective of this paper was to present the elastic property variations of hydrocarbon-bearing sandstones in Oil well A at Uzondu field, Niger Delta Basin, Nigeria using an integrated petrophysical and fluid replacement modeling (FRM). Five hydrocarbon-bearing sandstone reservoirs (Zones A–E) were identified within the depth interval of 8,100–11,470 ft, with a cumulative gross thickness of approximately 1,353 ft (412.39 m). Petrophysical evaluation indicates moderate to very high porosity (0.186–0.401), low water saturation (0.059–0.10), low clay volume (0.004–0.105), and moderate to excellent permeability (122.98–2,860 mD), confirming high-quality reservoir characteristics and strong hydrocarbon saturation across all zones. Fluid replacement modeling was applied to derive elastic parameters and evaluate depth-dependent stiffness variations. Compressional velocity (Vp) increases systematically from 5,693 ft/s in the shallowest reservoir to 13,475.8 ft/s in the deepest interval, while shear velocity (Vs) increases from 4,474 ft/s to 7,308 ft/s. Bulk density rises from 2.05 g/cc to 2.20 g/cc with depth. Correspondingly, acoustic impedance (Zp) increases from 11,671 to 29,647 ft/s·g/cc, and shear impedance (Zs) from 9,172 to 16,078 ft/s·g/cc. These progressive increases reflect burial compaction, porosity reduction, and enhanced rock stiffness rather than lithological variation, as all intervals are predominantly sandstone.