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Abstract

As Offshore Nigeria enters a third decade of deep-water exploration, unsuccessful wells in the structures of the deep-water Outer Fold and Thrust Belt have spurred a reevaluation of plays in the regional basin. Key lines from a newly-acquired seismic data set having 10 km long-offset, deep-tow acquisition parameters, and modern PSDM processing are examined here and show significant improvements in deep imaging. The interpretation of these lines advances the understanding the Paleogene Akata Shale and structural styles of mobile shale features and focuses new attention towards exploration leads of older sediments in intermediate water depths of the Inner Fold and Thrust Belt. The data show a clearer imaging of crustal structure, and the interpretation of the Tertiary supports the view of the offshore Nigeria as a linked extension to a contraction system driven primarily by gravity spreading. The Inner Fold and Thrust Belt of deep to intermediate water depths has been difficult to image in past data sets showing only thick sections of seismically opaque facies commonly interpreted as shale ‘diapirs’ and only thin sediments. Deep tow data here reveals several deep areas of stacked thrust sheets, within the Paleogene strata, as well as associated floor and roof detachments interpreted throughout the delta. The formation of these ‘duplexes’ uplifted existing Neogene thrusted sediments and folded these sediments often to very shallow depths where they are eroded near the present-day water bottom. Improved resolution of the lower Miocene and Oligocene sediments shows a robust deposition of these sequences that are involved in the inner belt structuring. The Inner Fold and Thrust Belt shows features that form a variety of hidden, deeper reservoir targets, structures of different timings, and areas where the deeper imbricates of the Akata could provide thickened source rock intervals.

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