Hydrocarbon Reservoir Rock Typing and Flow Unit Analysis in “D” Field, Offshore Niger Delta

ABSTRACT

Hydrocarbon reservoir is conventionally treated as a single rock unit, which adversely affects productivity. In most cases, this approach is unrealistic in complex geologic environment where reservoirs have several components that contribute to the flow of hydrocarbon. This study delineates reservoir rocks into its various rock types and flow units in “D” field, offshore Niger Delta. Suites of well log (gamma ray, resistivity, sonic, density, and neutron) from three wells and core data were utilized. Conventional method of flow unit analysis, involving flow zone indicator (FZI) approach, rock physics, and K ‐means clustering was adopted for the study. Two reservoirs, R1 and R2, were delineated, and their petrophysical properties were also computed. Petrophysical parameters showed that R1 has a gross thickness ranging from 7 to 14 m, whereas R2 ranged from 2 to 7 m. In R1, ( V _sh ) varied from 0.13 to 0.30, porosity ranged from 0.20 to 0.31, permeability varied from 1402 to 2947 mD, and hydrocarbon saturation ranged from 0.10 to 0.47. In R2, V _sh ranges from 0.17 to 0.32, porosity varied from 0.19 to 0.25, permeability ranged from 1247 to 2392 mD, and hydrocarbon saturation varied from 0.26 to 0.74. Three rock types, namely, poorly sorted unconsolidated sand, well‐sorted unconsolidated sand, and moderately cemented sand, were determined from compressional velocity ( V _p ) against porosity crossplot, superimposed on rock physics models. The well‐sorted and moderately cemented sandstones retained reservoir potential despite increased acoustic velocities, whereas the poorly sorted unconsolidated sands represent non‐reservoir facies due to poor consolidation and elevated clay content. Rock physics‐based K ‐means clustering identified four flow units in Reservoir R1 and three in Reservoir R2. Using FZI‐based K ‐means clustering, three hydraulic flow units were established in both reservoirs, which supports the rockphysics findings. FU1 exhibits the best reservoir quality. The integrated workflow has reliably characterized flow units in both cored and uncored reservoirs, thereby reducing reservoir uncertainty and supporting hydrocarbon recovery.