The Cretaceous Afikpo sedimentary Basin in Southeastern Nigeria contains rocks of fluvial, deltaic and shallow marine origin. This study examines the role of sedimentary processes in sediment distribution in the various geologic environments. The outcrop sections and the Afikpo River were studied by visual observation and photographing of important features during a field mapping exercise. Well log data from the Niger Delta Basin were also used to infer depositional environments based on gamma ray log motifs. These outcrop sections consist of fluvial, deltaic and shallow marine sediments that occurred as braids, point-bars, mouth-bars and beach/regressive bars. Braids and point-bar deposits also occurred within the recent Afikpo River channel, a major conduit transporting sediments to the offshore area of eastern Niger Delta. Sandstone outcrops showing a mouth-bar architecture occurred at Akpoha Town east of Afikpo Town, with a shallow marine sequence at Amasiri area, west of Afikpo Town. The Amasiri sandstone is a massive outcrop with large lateral extent covering more than 8 kilometers. Gamma ray log trends observed on well log from offshore area in the eastern Niger Delta indicated deposits of fluvial, deltaic and shallow marine origin.
Part of the book: Sedimentation Engineering
Sedimentary facies and structural lineaments represent significant control factors on hydrocarbon flow behavior. These geological elements have been evaluated to understand possible cause(s) of rapid decline in pro¬duction. The N5.2 reservoir, located in shallow marine sandstones, offshore Niger Delta, has experienced decline in oil rate with a corresponding increase in water-cut within two years of beginning of production. The main objective of this study is the determination of reservoir architecture in order to individuate the possible cause(s) of rapid production decline. To this aim, several methods have been used, including the seismic attribute analysis, electrofacies analysis, well log and petrophysical correlations. The obtained results show that the N5.2 reservoir is a massive sandy unit, occurring within the paralic Agbada Formation of about 2133 m thick. A contour depth map of the reservoir shows the occurrence of a structural saddle associated with an elongated closure having two structural culminations. Further analysis using the root mean square (RMS) and anti-tracking seismic attributes has indicated a seismic facies parallel to the paleo-coastline direction and several faults and fractures. The high quality of the reservoir, fractures, poor management and water injection may have induced rapid fluid flow and consequently early watercut and decline in production.
Part of the book: Sedimentary Processes