Structural controls on channel-related seismic facies distribution in the toe-thrust of deepwater Niger Delta

Deepwater gravitational settings are often characterised by active structures at, or near the seabed. Consequently, these structures exert significant control on sediment distribution especially on the distribution of reservoir-grade sediments often transported to deepwater by turbidity flows. This study investigates structural controls on the spatial and temporal facies distribution in the deepwater Niger Delta using 3D seismic reflection data. The study shows that the main seismic facies include: (a) channel-axis sands and channel levees; (b) sheet sands deposited immediately outboard of channel levees; (c) pelagic deposits; and (d) slump deposits. The distribution and overall geometry/architecture of these facies vary from the west of the study area (dominated by growing fault-propagation folds) to the east where a piggyback basin had developed, and bounded by a broad detachment fold. Reservoir grade sheet sands (splays) are common, and their deposition is triggered by a sudden increase in seabed gradient (between 0.8° and 4°) at fold locations. The spatial distribution of the splays is controlled by the distribution of seabed scarps - located on the forelimbs of growing folds. Splays deposited in sub-basins in the west of the study area are lobate-shaped (up to 10 × 15 km). In contrast, splays deposited within the piggyback basin have shapes that are elongated parallel to a growing detachment fold that is causing channels to divert. This study has provided great insight into the distribution of seismic facies in a complex deepwater setting, and in particular, into the temporal evolution of reservoir facies and their potential organization into hydrocarbon traps as they interact with growing structures through time.