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Tectono-Sequence Stratigraphic Interpretation of Late Miocene to Early Pliocene Deposits of Shallow Offshore, Niger Delta

Abstract

The study documents the regional stratigraphic framework and structural configurations of three blocks, H, J and K located in Shallow Offshore, Niger Delta. The purpose of the study is to use sequence stratigraphic framework, seismic facies and geomorphology and structural configuration as tools for prediction of reservoir distributions in relation to structuration. The dataset consists of 3-D seismic volume, wireline log suites (gamma ray, resistivity and sonic), biofacies, palynological and foraminiferal biozones and Niger Delta Chronostratigraphic Chart. A total of 15 wells drilled in these blocks within the last twenty years were studied. The ages (Ma) of the maximum flooding surfaces identified range from 3.9 – 11.5 Ma while that of the sequence boundaries range from 4.1 – 10.6 Ma. On strike there was a variation in the number of sequences from three to five and correlated wells tended to be older in age and shallower in paleobathymetry eastward. Flattening at 5.0Ma maximum flooding surface above 5.6Ma sequence boundary shows that updip, the system tracts gradually thin out eastward showing that rate of creation of accommodation increases westward. We attribute the increase in accommodation westward to the structural configuration of the area which allowed the formation of collapsed crest structures in the H block while the eastward decrease in accommodation is associated with closely spaced flank faults informally called the k- faults in the K block. Downdip, the correlation shows that individual system tracts thickened at the centre and thinned at the flanks. We interpreted this feature as channels in seismic with concave upward geometry at the centre with the thickened centre representing an incised valley created during base level fall at 5.6Ma sequence boundary which got filled at the next sea- level rise. Six seismic facies were interpreted, which delineate the distribution of lithofacies and their environments of deposition across the strike. Seismic geomorphologic characterization showed that the intensity of incision increases downward from 5.6Ma to 6.7Ma sequence boundaries suggesting high potentials for reservoir presence at deeper intervals and thus making prospectivity robust for deeper plays in the area.