Assessment of Well Log Correlation and Petrophysical Characterization of D1 Reservoir Sands in the OKW Field, Southeastern Niger Delta, Nigeria

Accurate reservoir characterization is fundamental to reserve estimation, hydrocarbon recovery optimization, and field development planning in clastic petroleum systems. This study presents an integrated well-log correlation and petrophysical evaluation of the D1 reservoir interval within the OKW Field, offshore southeastern Niger Delta, Nigeria, with the objective of assessing reservoir continuity, reservoir quality, and hydrocarbon potential. Wireline log data comprising gamma-ray, resistivity, neutron, density, sonic, and spontaneous potential logs from OKW 1, OKW 7 and OKW 10 were interpreted using a combination of stratigraphic correlation, neutron-density cross-plot analysis, and quantitative petrophysical evaluation. Gamma-ray correlation established the lateral continuity of the D1 sandstone unit across the field, confirming a regionally extensive reservoir package within the upper Agbada Formation. Cross-plot analysis successfully discriminated shale, brine-bearing sands, and hydrocarbon-bearing sands, thereby improving lithological and fluid characterization. Petrophysical results reveal significant variability in reservoir quality among the studied wells. OKW 1 exhibits a gross reservoir thickness of 210.70 ft, net-to-gross ratio of 0.97, effective porosity of 32%, permeability of 1,874.46 mD, water saturation of 36%, hydrocarbon saturation of 64%, and net pay thickness of 45 ft. OKW 7 records the highest effective porosity (37%) and permeability (3,651.06 mD), but its high water saturation (76%) and low hydrocarbon saturation (24%) indicate a predominantly water-bearing reservoir. OKW 10 represents the most prospective interval, with a gross thickness of 235.53 ft, effective porosity of 36%, permeability of 3,622 mD, low water saturation of 20%, hydrocarbon saturation of 80%, bulk volume water of 0.07, and net pay thickness of 137.61 ft. Comparative reservoir ranking indicates that OKW 10 possesses the most favorable combination of reservoir quality and hydrocarbon charge, followed by OKW 1, whereas OKW 7 is limited primarily by excessive water saturation despite excellent rock properties. The results demonstrate that hydrocarbon prospectivity within the D1 reservoir is controlled not only by porosity and permeability but also by fluid distribution and structural compartmentalization. This study provides the first integrated multi-well assessment of the D1 reservoir interval in OKW Field and establishes a quantitative framework for reservoir appraisal and future field development in offshore Niger Delta sandstone reservoirs.