--> Abstract: Contrasting Styles of Basin Floor Pans, Offshore Gabon, by G. G. Grant, M. Varadi, and H. Abou El Saad; #91012 (1992).

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ABSTRACT: Contrasting Styles of Basin Floor Pans, Offshore Gabon

GRANT, GEOFFREY G., Geco-Prakla Exploration Services, Woking, U.K., MARIA VARADI, Gaps Geological Consultants, London, U.K., and HESHAM ABOU EL SAAD, Geco-Prakla Exploration Services, Woking, U.K.

A recent sequence stratigraphic study of offshore central Gabon revealed that a range of styles and sizes of lowstand system tract basin floor fans was present. Integration of well and seismic data revealed that the most striking differences were between fan systems of Late Cretaceous and Late Eocene ages.

During the Late Cretaceous, basin floor fans characteristically extended only a few tens of kilometers seaward of the shelf break but often overlapped laterally to form a broad band of sand dominated suprafan complexes. These systems have produced well-defined fairways of high-quality reservoir sands trending approximately parallel to the contemporaneous shelf break. The best reservoir sands occur within the inner/middle fan, braided suprafan complex. The best reservoirs of the prolific Batanga Sand are found in braided suprafan complexes of the 71 Ma and 68 Ma lowstand systems tracts. Further reservoir prospects exist in relatively small depositional lobes at the mouths of meandering channels of the middle to outer fan.

By contrast, upper Eocene basin floor fans were found to be very elongate but laterally isolated fanlobe complexes. Within these systems major leveed feeder channels, up to 70 km long, cross the lower slope and basin floor. Sheet-sand systems were deposited over a wide area in the middle/outer fan at the mouth of the channel. Stacking of the sands has resulted in their characteristic lobate seismic expression. None of the Eocene fanlobe complexes have yet been tested offshore Gabon, but excellent examples are imaged by seismic in the deep water acreage recently offered for license.

The nature of the basin floor fan controls the location of the best reservoirs; therefore, characterization of the fan system is necessary for efficient exploration.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)