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V. Kolla1, P. Bourges1, P. Safa2
(1) Elf Exploration Angola, Roissy Cedex, CDG, France
(2) Elf Exploration Production, Pau, France

Abstract: Evolution and reservoir architecture of Tertiary deep-water meander channel and related depositional forms, offshore West Africa: Some new insights

Extensive 3D seismic attribute displays show that deep-water meander-channel forms are common in the subsurface Tertiary off West Africa. The high sinuosities, lateral and vertical stacking, meander cutoffs and avulsions of these channelforms determine their unique reservoir geometries. The various planform characteristics of these Tertiary channels are very similar to those of the recent deep-water and fluvial channels. However, the planform combined with sectional characteristics suggest that the high sinuous channels frequently developed through repeated channel aggradation on the convex bends and subsequently through lateral migration to the concave bends of initially low sinuous forms. In some cases, high sinuosities developed without much lateral migration and were maintained by vertical aggradation alone. The low-sinuous-straight channelforms may contain coarse-grained lags, sand and mud debris flows, and slump deposits indicative of extensive erosive-bypass phase, and the sinuous forms, high to low net to gross thick to thin sandy turbidites, indicative of accretionary fill phase. However, erosive-phase deposits may also be commonly present within sinuous channels. Further more, the lateral channel migrations may be discrete, separated from each other, or may be continuous seismically, always accompanied by aggradation. Fluvial point-bar type reservoir continuity is not expected across the entire extent of a deep-water sinuous belt, but may be present locally within it. The reservoir geometry of the deep-water sinuous forms may thus be very heterogeneous.

Associated with the sinuous channelforms, several types of lobe and sheet depositional forms develop at their termini and bends, and along their flanks. These forms, although generally characterized by high-amplitude seismic reflections, have different net-to-gross sand values and their reservoir geometries may be simple to very complex.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana