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Communications in Physical Sciences Vol. 2. No. 1, 35-49. (2017)
Authors: Chidozie Izuchukwu Princeton DIM., K. Mosto ONUOHA and Chukwudike Gabriel OKEUGO
Sequence stratigraphic, structural and reservoir analytical tools have been employed in interpreting the geology of the eastern Coastal Swamp Depobelt of the Niger Delta Basin. The aim was to understand the stratigraphic framework, structural styles and hydrocarbon reservoir distribution for improved regional hydrocarbon exploration across the onshore Niger Delta basin. This interpretative study made use of well logs, biostratigraphic (biofacies and bio-zonation) and petrophysical data obtained from twenty wellbores, integrated with recently merged and reprocessed 3D regional seismic volume spanning across eight fields. Results reveal the occurrence of nine key chronostratigraphic surfaces (five maximum flooding surfaces and four sequence boundaries) that were tied to well-established pollen and foram bio-zones for high resolution sequence stratigraphic interpretation. The sediment stacking patterns recognized from gamma ray log signatures were used in delineating the lowstand system tract (LST), transgressive system tract (TST) and highstand system tract (HST) genetic units. Well log sequence stratigraphic correlation reveals that stratal packages within the area were segmented into three depositional sequences occurring from middle to late Miocene age. Furthermore, there is thickening of stratal packages with corresponding decrease in net-to-gross thickness from north to south (basinwards). This is due possibly to the influence of syn-depositional structures on stratigraphy. The combination of reservoir sands (of LST and HST), source and seal shales (of TST and HST) and fault structures allows for good hydrocarbon accumulation and should be targeted during exploration. Reservoir evaluation studies using petrophysical parameters indicate the presence of good quality reservoir intervals, which are laterally continuous across several fields and partly compartmentalized within individual fields. Structural top maps of reservoirs show good amplitude response that are stratigraphically and structurally controlled. Structural analysis revealed the occurrence of back-to-back faulting, collapsed crest structures, simple/faulted rollovers, regional foot wall and hanging wall closures and sub-detachment structures. These structural styles constitute the major hydrocarbon entrapment mechanism in the area. Overall, the study has unraveled the existence of undrilled hydrocarbon leads at deeper depths that should be further revalidated for development.
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