Abstract:
Facies geometry, stratigraphic configuration, structural style, hydrocarbon type and distribution within the paralic Agbada Formation of Middle to Late Miocene age across several fields in the Eastern part of the Coastal Swamp depo-belt were studied using regional 3D seismic, wire-line well logs and biostratigraphic data. The study involved analyses of sequence stratigraphic framework across nine fields using information obtained from twenty- four wells. Ten major stratigraphic bounding surfaces (five each of sequence boundaries (SB) with ages ranging from 13.1 Ma through 8.5 Ma. and maximum flooding surfaces (MFS) with ages between 12.8 Ma. and 7.4 Ma respectively) were identified, correlated and mapped across several wells and seismic sections. Four depositional sequences were delineated and stratigraphic flattening at various MFS(s) indicates that there is a shift of the depositional center from north to south. Three major stacking patterns (progradational, retrogradational and aggreadational) were delineated and interpreted as Lowstand Systems Tract (LST), Highstand Systems Tract (HST) and Trangressive Systems Tract (TST) using their bounding surfaces. The alternation of the reservoir sands of the LST and HST and the shale units of the TST offers good stratigraphic traps for hydrocarbon. The Gross Depositional Environment spans through incised Canyons, Channels, Inner Mid Shelf, Shelf Margin and Slope Margin. Paleobathymetric maps show generally, that sediments were deposited within Neritic through Bathyal environments at different times, aligning with the progradational pattern of deposition of the Niger Delta. Structural analyses reveal the occurrence of Back to Back Horst Block (Trapezoid Zone), Collapse Crest Structures, Simple/Faulted Rollovers, Regional Foot Walls/Hanging Walls and Sub-detachment structures dominating within the mainly extensional zone and these constitute the major hydrocarbon traps in the area. Revalidated and newly identified leads at intermediate and deeper horizons indicate that detailed mapping of stratigraphy and structures are critical in hydrocarbon evaluation of deeper prospects in the Niger Delta.
