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A Submarine Depositional System With Straight Channels and Slope Aprons: Niger Delta Continental Slope


The deep-water plays of West Africa have been prolific producers in the last few years, and remain an important exploration area. A key challenge in unlocking the potential of such plays is in understanding the degree to which common deep-water facies architecture models apply vs. the degree to which local conditions control the reservoir architecture. Here we use high-resolution 3D seismic data to illustrate development of a turbidite system on the mid-slope of the Niger continental margin: the Bakana Submarine Depositional System (BSDS). The system changes in depositional element type along flow direction from lobes, to straight channels to slope aprons over some 18 km. The lobes comprise three overlapping lobe complexes varing in size from 1200 - 4000 m in width and 15 – 30 m in thickness and 8 – 11 km in length. Turbidity current flow pathways and hence the geometies of the lobe complexes are controlled by the orientation of growth faults in a minibasin with limited subsidence-related development of accommodation, focused within local grabens. The lobes transition downstream into parallel, straight channels that are mostly clustered adjacent to each other. These channels are relatively small at 150 – 200 m in width and 30 – 45 m in depth with typical width to depth ratios of 4 to 5; they deeply incise the underlying strata. Channel fill is mud-dominated in the upper reaches, but sand-dominated downstream. These straight channels are associated with significant increase in slope gradients (from <2° to >3°). The straight channels transition down-current into slope aprons that are some 2,100 to 3,100 m in length, 600 to 1,700 m in width, 10 to 30 m in thickness, showing a gradual increase in the proportion of muddy deposits along localised flow directions. Although the slope aprons usually overlap with each other, connectivity between them is low due to an increase of mud-prone deposits radially along the slope. The slope aprons develop where the slope decreases abruptly from >3° to <2°. The localised slope gradients and growth faults play an important role in the variability of the BSDS. This conclusion emphasises the importance of assessing local controls during exploration and production of deep-water reservoirs.