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Abstract: Improved Reservoir Prediction of a Mixed Siliciclastic-Carbonate Platform by Using High-Resolution Sequence Stratigraphy (N'Kossa Field, Offshore Congo)

Bruno Caline, Herbert Eichenseer, Patrick Calatayud, Fred Walgenwitz, Bernard Le Theoff

The poster illustrates how the recent developments in genetic stratigraphy have contributed to constrain reservoir layering and to improve prediction of reservoir quality in the oil-bearing reservoir of N'Kossa. The mixed lithology deposits formed during Albian times.

Thanks to the excellent core coverage of the reservoir (4 cored wells over the entire reservoir interval), continuous sedimentological examination and interpretation of the facies succession have been carried out. The reservoir can be subdivided into composite sequences (50 to 150 m thick) which are made up of stacked metre-scale genetic units. Three different stacking patterns of genetic units have been identified; retrogradation, aggradation and progradation. These patterns reflect a gradual change of depositional regimes through time. Facies variations (texture, bio-association, geometry, spatial distribution) and early diagenetic overprints can be related to each type of stacking pattern. One additional model illustrates the depositional regime corresponding to low accommodation p riods which mainly record siliciclastic input and extensive carbonate diagenesis by meteoric waters.

The resulting four models show the overall distribution of the main depositional units, the diagenetic zonations and the resulting overall reservoir qualities.

This above approach have contributed to a more detailed reservoir architecture and a better delineation of reservoir heterogeneity due to both depositional and diagenetic regimes.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France