Deepwater Reservoir Architectures of the Bonga-SW/ Aparo Field

Andrew R. Hoover
Shell International Exploration & Production, Houston, TX

Discovered in April 2001, the Bonga-SW/Aparo field straddles OPL212, OPL213, and OPL249 in water depth of 1250m offshore Nigeria, 10km southwest of Bonga field. Appraisal wells have confirmed multiple oil accumulations in structural/stratigraphic traps. The unconsolidated Miocene age reservoirs have excellent reservoir properties.

Bonga-SW/Aparo comprises multiple reservoir intervals, each with multiple sands and/or reservoir compartments. An upward succession of reservoir architecture styles suggests two periods of slope profile evolution. Each succession progresses upward from 1) lobate sands deposited in ponded/healed slope accommodation to 2) amalgamated channel sands to 3) incised canyon fills. This succession of architectures also represents a relative increase in reservoir complexity on the seismic and sub-seismic scale.

External seismic geometries of the lobate reservoirs support a depositional model wherein channels trending NE-SW feed lobe complexes on the flank of the present-day Bonga-SW/Aparo structure. Lobe sands tie to laterally continuous high amplitude seismic events correlating to high-quality sands.

Log and core data from amalgamated channel sands exhibit significant vertical and lateral facies variation in addition to channel-base shale drapes.

Incised canyon fill reservoirs record a complex history with repeated episodes of erosion, bypass, and deposition. These episodes result in a complex heterolithic fill and multiple significant bypass surfaces that increase potential for baffles and barriers to flow within the canyon fill complex.

With faults superimposed on stratigraphic complexity, it is important to assess uncertainties and mitigate risk. Initial wells will target high-rate high-ultimate reservoirs while further appraising additional reservoirs to be developed as needed to maintain production plateau.