--> Influence of Slope Gradient on Reservoir Distribution and Architecture in Slope Setting - An Example from Offshore Niger Delta, Nigeria, by Adedayo Adeogba, Timothy R. McHargue, and Stephen A. Graham; #90037 (2005)

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Influence of Slope Gradient on Reservoir Distribution and Architecture in Slope Setting - An Example from Offshore Niger Delta, Nigeria

Adedayo Adeogba1, Timothy R. McHargue2, Stephen A. Graham3
1 ChevronTexaco Overseas Petroleum, Houston, TX
2 ChevronTexaco Exploration Technology Company, San Ramon, CA
3 Stanford University, Stanford, CA

A near surface 3-D seismic dataset from offshore western Nigeria, Niger delta slope, was studied to gain further insight into controls on channel-fan architecture and reservoir distribution in slope settings. Insights gained from this study permit the development of predictive analog models for application to reservoir systems at deeper prospective intervals. Synsedimentary extensional faulting and mud diapirism form major structural/topographic controls on deposition from sediment gravity flows in this slope setting. These controls are exercised principally through changes in slope gradient, which have profound effects on fan development and inferred sand distribution. The mechanism for fan aggradation is likely through hydraulic jump at abrupt reduction of slope gradient. Channel incision results from development and headward migration of knick point in response to adjustment of the equilibrium profile at an abrupt increase of slope gradient. Lithofacies inferred from observed seismic character and seismic stratigraphy, in lieu of borehole data in the area, include mass transport complexes, distributary channel/lobe complexes, and hemipelagic drape complexes, reflecting a combination of active (sediment input from channel systems) and relatively passive (slope failure and slumps) sediment supply systems. Leveed channel complexes are absent in this study area. Fans that show evidence of channel incision and bypass are termed 'transient', whereas fans without channel incision are termed 'terminal'. This distinction has implications for both exploration and reservoir management. The presence of incised channels in transient fans indicates bypass and transportation of sand to locations farther basinward. Hydrocarbon reservoirs in transient fan settings could be significantly compartmentalized by incised channels which are very often shale filled.