--> Seismic Architecture of Outer Shelf Canyon Segments in the Lüderitz Basin, Offshore Namibia

2018 AAPG International Conference and Exhibition

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Seismic Architecture of Outer Shelf Canyon Segments in the Lüderitz Basin, Offshore Namibia

Abstract

The Lüderitz Basin is the least explored basin of the Namibian passive continental margin. So far one exploration well has been drilled on the outer shelf, but the 2D and 3D seismic coverage is fair. Working petroleum systems have been proven with the Kudu Gas Field in the adjacent Orange Basin to the South and with the oil shows in the Wingat-1 well in the Walvis Basin to the North. Seismic imaging reveals a number of canyons and submarine fan systems along the entire Namibian passive margin. For this study the canyon architecture in the outer shelf of the Lüderitz Basin has been analyzed using 2D sections. Seismic imaging reveals external canyon geometry as well three distinct seismic facies of the canyon fills. Conspicuous erosive surfaces developing downwards from the near Base Tertiary Unconformity and from an Intra-Santonian unconformity delineate the external canyon geometry. Canyons incise as deep as into the Albian, implying that they formed during major lowstands. Canyons are typically V-shaped and exceed 10 kms in width and can be more than 500 ms TWT deep. Seismic facies of the canyon fills include discontinuous to chaotic reflections occurring in the basal canyon fills and along the lower flanks, followed by a second seismic facies of more continuous moderate amplitude reflections that partially mimic the flank geometry. Horizontal to slightly mounded high amplitude continuous reflections characterize the third seismic facies that dominates the upper canyon fill and drapes the canyon walls. The three seismic facies are interpreted as 1) debris flows and slump deposits originating from unstable canyon walls, 2) as transgressive estuarine-fluvial deposits, and 3) as submarine sediment drape, respectively. Sand bars in the estuarine-fluvial facies are potential hydrocarbon reservoirs. Furthermore, the canyons architecture assists in predicting reservoirs in the associated down-dip submarine fans.