Exploration Significance of the Tectono-Stratigraphic Evolution of the Eastern Benin Basin, Offshore Nigeria
Etobro, Israel A.; Watkinson, Matthew P.; Anderson, Mark W.
This presentation results from the first academic study on the offshore Benin Basin using integrated 2-D, 3-D seismic and well data. This basin has become the focus of increased exploration interest in the light of the discovery and on-going development of the Aje gas condensate and oil field, and the Gulf of Guinea province in general.
The main objective of this study is to evaluate the tectono-stratigraphic evolution of the basin, and to use this to identify potential future prospectivity in this region of offshore West Africa.
Three megasequences typify the study area: syn-rift, early post-rift and late post-rift. The syn-rift megasequence (early Cretaceous) consists of two main sequences representing both early syn-rift and syn-rift climax phases. The sequence of the syn-rift climax phase is composed of moderate to high amplitude wedge-shaped configuration, with reflectors diverging towards the basin-bounding faults. There is no direct evidence for transform related tectonics. However, syn-rift normal faults dip northwards towards the onshore in this region rather than ocean-ward. The timing of the syn- to post-rift transition appears to differ between adjacent half-grabens, with syn-rift phase continuing later in more external basins. This could be accounted for by on-going rift linkage or strain localization towards the rift axis prior to ocean-crust generation.
The early post-rift megasequence is composed of a number of sequences, thought to be of Cenomanian to Late Palaeogene age. Initially shallow-marine depositional patterns were strongly controlled by the preceding rift architecture. Subsequent slope and deeper water sequences were controlled by the interplay of eustatic sea-level change and downslope extensional slope failure, and their temporal and spatial effect on accommodation creation. Of particular importance are syn-depositional up-slope propagating gravity generated extensional fault arrays, which created slope canyons in the Late Cretaceous and Palaeogene. The late post-rift megasequence is a Neogene progradational sequence set revealing a regressive marine setting. Downdip, during the forced regressive and early lowstand part of these sequences, mounded submarine fan facies found on the slope and basin floor can serve as potential reservoirs for petroleum.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013