Reservoir and sequence stratigraphic analysis using subsurface data
AbstractThere is a growing interest in the Niger Delta hydrocarbon field exploration and exploitation. With growing interest in proven field prospects and confirmed reservoir facies, there is a need for improved basin and field scale reservoir identification, analysis, and assessment. The Agbada Formation of the middle Miocene age across Vim Field, in the western part of the coastal swamp depobelt was studied using wire-line logs, 3D seismic and biostratigraphic data. This contribution evaluated stratigraphic configuration, structural style, facies geometry, hydrocarbon leads, and distribution. The method adopted involves delineating lithologies from the gamma-ray log, identifying reservoirs from the resistivity and gamma ray logs, well top correlation using gamma ray logs, horizon and fault mapping, time to depth conversion of maps using velocity model, attribute analysis, and sequence stratigraphic analysis. Bounding surfaces were mapped on the seismic section, and well correlations were conducted and integrated with a paleobathymetry chart to highlight the depositional environments. Eight major stratigraphic bounding surfaces (four sequence boundaries and four maximum flooding surfaces) were identified. Erosional bounding surfaces were mapped as interest surface horizons. Analysis of the vertical succession of depositional facies revealed five 3rd order depositional sequences of Mid-Miocene age-bound SB and MFS chronologically. Three strata stacking patterns (progradational, retrogradation, and aggradational) were delineated and interpreted as lowstand systems tract (LST), highstand systems tract (HST), and transgressive systems tract (TST). The alternation of the reservoir sands of the HST and TST and the shale units of the TST offers good traps for hydrocarbon. Fault analysis revealed regional growth faults, counter-regional growth faults, synthetic and antithetic faults that show foot walls and hanging walls dominating the mainly extensional zone. These faults play a major role in hydrocarbon trapping within the area. The depositional environment spans from shelf to slope margin, with sediments deposited within the Inner neritic through the middle neritic to the outer neritic settings. Interpretative observation shows that thin-bedded shale facies complexly intercalate the reservoir facies of the TST. Thus careful evaluation of such reservoirs is recommended before making exploitation decisions.