--> ABSTRACT: Reservoir Architecture of a Fine-Grained Basin Floor Fan Complex, by Arnold H. Bouma, H. DeVille Wickens; #91020 (1995).

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Reservoir Architecture of a Fine-Grained Basin Floor Fan Complex

Arnold H. Bouma, H. DeVille Wickens

The Permian-aged Tanqua Karoo subbasin, South Africa, contains fine-grained basin floor fan deposits, that have been uplifted with only a minor tilt in one direction. This permits excellent lateral correlation between the cliff-type outcrops, revealing a succession of major architectural changes in a downdip direction. Updip a channel complex is comprised of several successive channels that have eroded into each other. Remnants of shale-rich thin beds (levee accumulations) occur between the channel fills. This causes a very tortuous reservoir flow pattern.

Downdip this channel complex changes into individual massive channel fills "imbedded" in layered, mostly thin-bedded sandstones that can be better interpreted as levee-overbank deposits rather than distal fan accumulations. A few physical connections between layers and the massive channel sandstone can be observed.

Downdip the channel shape gradually becomes less distinct and the overall ss/sh ratio increases. The channel-levee-overbank deposits transfer into depositional lobes or sheet sands. They consist of very flat lenticular sandstone bundles, comprising 6-8 amalgamated sandstones that are only partially in communication with each other. The bundles onlap onto each other with shales separating them. Individual bundles can be up to one kilometer wide and 20 meters thick.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995