Genetic Sequence Stratigraphy of the Oligocene-Miocene Niger Delta: Seismic Responses, Biostratigraphic Resolutions and Hydrocarbon Occurrence

Douglas O. Anunugwo¹, E. A. Ayolabi², and L. Adeoti^2
1 ECCO Petroleum Services, Lagos, Nigeria
² University of Lagos, Lagos, Nigeria

The Oligo-Miocene sequences of the Onshore Niger Delta have been defined based on detailed sequence stratigraphic concept and the techniques. Depositional sequences are fundamental part of the stratigraphic records which reflects changes in relative sea level and sedimentary processes.

This paper focuses on the recognition of depositional cycles from seismic profiles integrated with wire-line logs and the paleontologic information from five wells. Based on this integration, foraminiferal abundance/diversity paleobathymetric data and the abundance of authegenic minerals (glauconite) were used in locating condensed sections, maximum flooding surfaces (MFS) and sequence boundaries. These boundaries were dated using age diagnostic and significant foraminifera of the Niger Delta, and were tied to the Global Eustatic Cycle. Variations in the foraminiferal abundance/diversity, lithology and mineral occurrence were used to characterize the different depositional systems tracts. A model for the recognition of third order cycles, systems tracts and depositional boundaries was developed. The model is useful also for the prediction of the presence of good quality reservoir sands.

The system tracts show characteristic lithology patterns. The lowstand systems tracts show alternations of sands and shale lithologies. These are characterized by sand-rich coarsening upwards units where reservoir quality is excellent. This highstand systems tracts characterize by shale-rich upward coarsening sand where the reservoir quality are generally poor. While the transgressive systems tracts characterized by thick units of shales may be present as good quality seals to reservoirs.