Interpretation of Depositional Environment of Rho Field Using Sequence Stratigraphic Analysis, Shallow Offshore Depobelt, Niger Delta

Abstract

Candidate Maximum Flooding Surfaces (MFS) identified on Rho-1, Rho-2 and Rho-3 were the basis of correlation across the wells for sequence Stratigraphic analysis in the field. Three (3) candidate MFS which include MFS-1, MFS-2 and MFS-3 were identified using the method adopted by Okoli [1]. Erosional surfaces were also delineated in wells from the observed stacking pattern between a sequence from Galloway model (1989) leading to the correlation of SB-1 and SB-2 across the wells. Using the Galloway model, four (4) depositional sequences were inferred SEQ (1-4). In the first sequence (SEQ 1), deposition occurred in a transgressive episode. Depositional environment was interpreted from electrofacies and revealing stacked sequences of reservoirs predominantly composed of fluvial channels which incised the Upper and Lower Shorefaces on a delta front system. In SEQ 2, looking at the aggradational pattern of the sequence, the formed channels were under the influence of both tidal and fluvial systems. In SEQ 3 and 4, based on electro-facies, the stacked reservoir sands were deposited predominantly in a shoreface/delta front environment and channel incisions in a wave subjugated high energy deltaic setting. The entire well section showed deposition in a regressive phase. Proposed conceptual models were generated using Petrel software and could be used as an input reconstruction of subsurface geological models. Indicating correct orientation of geo-bodies and facies belts (pinch outs of sands and shales), depositional dips and gross permeability architecture.