NAPENews Magazine September 2022 Edition

LAGOS BUSINESS MEETING
Deepwater assets offshore of the Niger Delta have produced tremendous volumes of hydrocarbons. Quantitative
development costs and resource estimations are driven by 3D and 4D earth and simulation models that require
continuous tuning and modification as dynamic reservoir, and facility conditions change with time as a function of
production. As initial conditions change and new data is collected, so does the need to adjust and improve
subsurface models. There are many techniques for accomplishing this, each with varying levels of complexity.
Stratigraphic relationships routinely serve as a large uncertainty in complex deepwater systems. Adding to this
complexity is the dynamic behavior of the reservoir as continued production and secondary recovery techniques are
employed.
To better understand the relationship between historic production performance and the predictive accuracy of
forward models in deepwater assets, a 3D/4D seismic analysis was performed to help characterize subsurface
relationships to explain unpredicted injector-producer waterfront behavior. The importance of accurately
characterizing reservoir architecture is paramount and driven by turbidite flow phase (waxing-waning flow cycles),
aggradation rate, compensational stacking, bathymetric morphology, and grain-size. Seismic geomorphology,
together with log-based stratigraphic approaches were applied to a mature deepwater asset to improve the
characterization, explain unpredicted production dynamics, and assess future development opportunities.
Results demonstrate that the reservoir is represented by thick- compensationally stacked early-stage channel
complexes ranging from erosively confined disorganized sand-rich flow deposits in the fairway axis, to thinner laterstage
organized levee-confined deposits along the flanks. Synchronized system tracts analysis (structural and
Wheeler domain) togetherwith seismic attribute analyses (spectral decomposition and instantaneous attributes) reveal distinct discontinuities between adjacent channel
complexes that tend to amalgamate and disappear updip. The down-dip separation of the erosionally confined channel complexessuggests that they are laterally
disconnected and form preferential flow-units along the depositional axis. Consequently, the occurrence of separate down-dip flow-units directly influence the dynamics and
direction of water movement from the aquifer and water injection wells. The integration of seismic stratigraphy and well section analysis helped define the depositional
architecture of thereservoir which was used to identify the major stratigraphic depositional trends that constrain communication in the reservoir.
The result of this study was used to optimize the future development strategy for this reservoir to maximize the expected ultimate recovery (EUR). These new seismic
stratigraphic workflows provide a clear basis for future application and utility in exploration and production.
NAPENEWS AUG/SEPT 2022 56