Seismic Stratigraphy of the Toe-Thrust Region of the Niger Delta Slope: Linking Structural Evolution to Basin Fill History

Abstract

In the deep-water slope areas of the southern lobe of the Niger Delta, gravity-driven deformation has resulted in the development of a fold and thrust belt since middle Miocene times. Over time the interaction between tectonically driven sea-floor topography and sediment dispersal systems have allowed for the formation of structural and combined traps. The typical reservoirs comprise large channel complexes and sheet sands, but their distribution is controlled by the rate of structural deformation versus sediment accumulation. A 3D seismic survey covering an area of 6200 km2 is used to map the facies and structural evolution of five piggy-back basins defined by growth strata and bounded between thrusts-propagation folds at toe-of-slope region. Due to the diachronous formation of the thrust-folds, the boundary between pre-growth and syn-growth is seen to vary across the toe-of-slope region, so that any syn-growth sequence might correlate to a pre-growth sequence on thrust-folds developed at later times. Within the syn-growth interval of the most seaward piggy-back basin three main units, which record the evolution of the basin, have been mapped and four main seismic facies have been interpreted from seismic amplitude extraction maps; these are channel-complexes, lobe deposits, mass-transport complexes and background slope hemipelagic muds. The relative abundance of these deposits, their assemblage and architecture is seen to vary within the three main mapped units. In general terms, the vertical stratigraphic trend shows predominance of channel-levee complexes in the older section whereas mass-transport deposits are common in the younger parts. The seismic-stratigraphic mapping has been integrated with measurements of structural strain across the thrusts bounding the most seaward piggy-back basin. Results show that periods of relative, low, strain-rate correlate with laterally shifting channel-levee complexes, whereas during periods of high strain-rate, channels tend to stack vertically. Stratigraphic mapping and measurements of structural strain in the adjacent basins upslope will test the results obtained for the most seaward piggy-back basin. The results will reveal the overall structural evolution of the region and new information will be provided on how these piggy-back basins are filled. The application of this study will include a more accurate prediction of reservoir facies distribution as well as prediction of stratigraphic and combined traps.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017