Abstract: Sequence Stratigraphic Prediction of Reservoir and Source Deep-Water Angola Block 24

Brock, Dennis and Laura Smith - Mobil New Exploration and Producing Ventures; and Rick Sarg - Mobil Technology Co.

Block 24 in the Benguela basin offshore Central Angola comprises a salt withdrawal minibasin province. Sequence stratigraphic analysis indicates deep-water siliciclastic deposition dominated the Upper Cretaceous through Tertiary history of the block. Onshore geologic control suggests first cycle siliciclastics from a mixed granitic and metamorphic terrane were transported into the basin. Depocenters shifted northward with time reflecting sequential sediment loading and evacuation of the salt basinward. The arcuate morphology of salt ridges left rimming the basin supports the northward direction of progradation inferred from sediment distribution patterns.

Onlapping parallel to low-relief mounded amplitude packages located within the depositional thicks are interpreted as deep-water gravity flow deposits that accumulated in salt withdrawal lows. The dominantly parallel and continuous reflection configuration of the amplitude packages suggests a sheet sand geometry. Observed AVO response varies from type III or II in the Tertiary grading with depth to type I in the Cretaceous.

Upper Cretaceous organic-rich marine shales are interpreted to drape and onlap rotated blocks of Albian carbonate and fill initial salt withdrawal lows. Equivalent post-salt source rocks in wells on adjacent nearshore blocks show a similar seismic geometry. 3-D geochemical modeling indicates that these potential source beds began generating in the Oligocene. The modeling provides a match to low maturity oil seeps recovered over salt features adjacent to the generating minibasins.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil