Michael W. Webb¹, Katherine A. Kanschat², Roger B. Bloch², James Younger K. Blevins³, Andrea Fildani⁴
(1) University of Wyoming, Laramie, WY
(2) Mobil Technology Company, Dallas, TX
(3) Mobil Equatorial Guinea, Inc, Dallas, TX
(4) Stanford University, Stanford, CA

Abstract: Contrasting canyons: 3D seismic interpretation of shallow (Pleistocene to Recent) shelf to slope depositional systems, Equatorial Guinea

Approximately 2400 km2 of 3D seismic data covering outer shelf and upper slope depositional environments offshore Equatorial Guinea were interpreted in order to elucidate trends of and controls on reservoir geometries. The study area is located at the regional bend in the west African continental shelf fed by the Niger and Cross Rivers. Sediment fairways within the slope are constrained to flow west-southwest, focused by canyon systems.

The sinuous Calabar Canyon is active in this region, demonstrating successive periods of cut and fill that extend upslope into shelf deltaics. The Calabar is erosional at its head, aggradational further downslope, and commonly exhibits slumped margins. In contrast are a series of regularly spaced, older canyons located to the west whose origins and geometries have been influenced by regional toe thrusting and tear faulting. These canyons are presently dormant, and exhibit linear chute-like geometries that do not reach the shelf edge. At least one of these canyons is underlain by an earlier sinuous system that intersects the shelf. The sinuous-to-straight evolution of these canyons is poorly understood, but channel-margin and downslope slumping appear to have played a significant role.

There appears to be a positive correlation between sinuous and/or aggradational canyon systems and their intersection with the shelf, as evidenced by the similarities between the modern Calabar and the ancient western canyon system. In providing analogues for reservoir geometries at depth, this study emphasizes the need to establish a clear stratigraphic link between shelf and slope settings.

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