Miocene Deltaic Sequence in the X- Field, Northwestern Niger Delta: An Integrated Sequence Stratigraphic Approach

U. Odumah and B. D. Ako
Obafemi Awolowo University, Ile-Ife, Nigeria

Sequence stratigraphic analysis was performed on four wells in the X-field, northwestern Niger Delta. The data used were petrophysical well logs (Gamma ray (GR), Resistivity (ER) and combined Neutron (CNL)-Density (FDC) logs), 2-D seismic sections and high resolution biostratigraphic data. The data sets were analyzed independently of each other and later the results were integrated. The stratigraphic surfaces viz: sequence boundary, maximum flooding surfaces and top of lowstand were identified on both the logs and biostratigraphic datasets and necessary seismic criteria were employed in mapping the stratigraphic surfaces. The results showed that the area consists of depositional sequences of third order cyclicity of early-middle Miocene age. Three sequences, which fall within two of the cyclical depositional cycles (Cycles 6 and 7) that make up the sequence stratigraphic framework of the Niger Delta, were identified. These three sequences are composed of three marine transgressive shale markers namely: 15.4 Ma Chiloguembelina-3, 17.4 Ma unnamed and 19.4 Ogara shale markers. The associated systems tracts were identified in the course of this research. Each sequence contains a transgressive and highstand systems tract, which are said to be the main producing reservoirs of the Niger Delta. Its thick lowstand systems tract made up of basin floor and slope fans appeared to be potential reservoirs of oil and gas. Sequence III is bounded by a type II unconformity but seems to lack its associated shelf margin systems tract probably due to high degree of faulting in the area of pinch outs. The application of the sequence concept in this research has not only contributed to the stratigraphy of the study area but has also allowed the recognition of potential reservoirs within the lowstand systems tract and possibility of stratigraphic trap in the untested deeper (LST) of the study area.