Roger B. Bloch2,
Michael W. Webb3
(1) Stanford University, Stanford, CA
(2) Mobil Technology Company, Dallas, TX
(3) University of Wyoming, Laramie, WY
Abstract: Evolution of Pleistocene channel-levee systems offshore Equatorial Guinea, West Africa
A buried Pleistocene channel-levee system imaged on 3D seismic offshore Equatorial Guinea provides insights into the temporal evolution of reservoir geometry in a sequence stratigraphic framework. The study area is located on the outer shelf and upper slope southeast of the Niger Delta. Stratigraphic links from the shelf edge to slope setting have been established and specific controls on geometries and processes focussing on the overall evolution of the shelf-to-slope system were identified. Two transgressive surfaces serve as top- and base datum horizons for the channel-levee system. The system was analyzed using time slices and proportional horizons between these two horizons for extraction of seismic amplitude maps. The channel-levee system, strongly depositional and characterized by high sinuosity, developed during a relative lowstand of sea level, as determined by correlation to the penecontemporaneous shelf strata. A subdivision of the lowstand stage was possible due to the contrasting characteristics of the early lowstand systems tract (LST) vs. the late LST. During the early lowstand, the system bypassed the shelf; the submarine channels pinch-out by onlap on the upper slope. The early LST channel-levee system has a low-aggradation character with a well-defined, broad, laterally amalgamated channel belt. During late lowstand, the channel-levee complex was fed by prograding clinoforms on the shelf-edge and has a highly aggradational character. Late lowstand channels are more laterally isolated, with well defined overbank deposits. Potential applications of these results to deeper targets are great. The identification of different stages in channel-levee systems allows reservoir geometry prediction.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana