Scours: Occurrence, Measurement, and Importance in Deep Water and Shallow Water Depositional Systems
John Snedden1, Paul A. Dunn1, Benjamin Sheets2, and John C. Van Wagoner1
1ExxonMobil Upstream Research Co., Houston, TX
2ExxonMobil Production Co., Houston, TX
Scouring at the base of channels and at channel mouths may play a significant role in enhancing vertical connectivity of reservoirs. Assuming accurate depth conversion, scours measured in both East Breaks Upper Fan (Quaternary) and Iron River Valleys (Cretaceous) are comparable in scale, with a typical weighted average of 10 to 15 m scour depth. Experimental datasets show development of scours under jet-generated turbulence, comparable in relative scale to East Breaks and Iron River seismically-defined scours.
Factors considered as possible controls on scour occurrence, depth, and spacing are slope gradient, substrate lithology; and planform geometry (e.g. bends, constrictions). Results indicate that neither gradient nor substrate lithology appear to greatly influence scour depth or location in the datasets analyzed.
Planform geometry (sharp turns in channel thalweg) appears to show a qualitative association with deep scouring in East Breaks (Quaternary) channels. In the Iron River (Cretaceous) heavy oil field, scour spacing shows a potential relationship with bankfull width, per the relationship derived from modern fluvial channels, though the reach length was restricted here.
Among the potential implications from this study are that channel base scour depths and locations are most influenced by changes in channel orientation in a deepwater system where sediment gravity flows are episodic. In a fluvial system where flows are interpreted to be more temporally continuous, scours and the jets that form them may become better established temporally and the pool spacing relationship with bank full width (5-7x of Keller and Melhorn, 1978) may apply.
Scours create discrete, subseismic connections between reservoir compartments which must be included when constructing geologic models to simulate and match production histories.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery