Professional Application of Downhole Geophysical Logging in Characterising Reservoir Properties in the Niger Delta Basin

Downhole geophysical logging provides continuous high-resolution measurements of formation properties that are essential for reservoir characterisation in Niger Delta oil fields, yet optimal log selection, quality control, and petrophysical interpretation remain areas where professional practice varies widely across operating companies. This study evaluates the application of an integrated well log suite, including gamma-ray, resistivity, neutron-density, and sonic logs, for reservoir property characterisation in four producing wells in an onshore oil field in Rivers State. Log quality was assessed using standard repeatability checks and environmental correction protocols. Shale volume was calculated using the linear gamma-ray index, and results were compared with the Larionov correction to assess the effect of radioactive sands in the Niger Delta context. Formation water resistivity was estimated from the Pickett plot method applied to water-bearing intervals identified by crossplot analysis of neutron-density and resistivity logs. Porosity values derived independently from density and neutron logs were reconciled using a crossplot interpretation, yielding average effective porosity of 26 to 32 percent in the main reservoir sands. Water saturation was calculated using both the Archie and modified Simandoux equations. Comparison with core-derived porosity and saturation data from one of the four wells validates the log-derived estimates with correlations exceeding 0.92. The study establishes a quality-controlled petrophysical workflow applicable to reservoir appraisal in Paleogene and Neogene Niger Delta sequences. Keywords: well log analysis, petrophysics, Niger Delta, reservoir characterisation, porosity