--> Abstract: Variability in Channel-Belt Basal Scour Surface and Implications for Connectivity Between Channel-Belt Reservoirs, by Neal Alexandrowicz and John Holbrook; #90078 (2008)

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Variability in Channel-Belt Basal Scour Surface and Implications for Connectivity Between Channel-Belt Reservoirs

Neal Alexandrowicz and John Holbrook
Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX

Assessment of potential for draining un-penetrated but closely stacked channel-belt reservoirs from an existing belt penetration depends upon an understanding of the methods of and the likelihood for connectivity between otherwise isolated reservoirs. Knowledge of both the variability in scour depth beneath belts and the belt lithofacies and architecture is critical for making such assessments, yet is very poorly understood. We reviewed a collection of over 500 driller’s records along a 75 mile stretch of an active Mississippi River meander belt. We divided the lithofacies into genetic units and recorded the depth of significant surfaces between units. Two trends are evident: 1) The variability of the basal scour surface of the belt mimics the variability of the modern channel thalweg depth through the studied belt, and 2) While the Mississippi River is the classic example of a mud dominated fluvial system with abundant abandoned meanders, much of the lower abandoned channel fill is not composed of passive-fill clays, but rather a grittier mix of active-fill mud and sand of variable permeability. Our results suggest that, if channel-belt reservoirs are vertically separated by the thickness equivalent of one-half the average thalweg depth (average channel-fill or belt thickness as proxy) they should be able to connect through the scour surface across 15% of the overlapping belt area. As the thickness of the separating unit approaches the equivalent of the average thalweg depth, the likelihood of connectivity between potential reservoirs decreases to less than 1%. Once connected by the scour surface, communication between stacked channel-belts also depends on the reservoir quality. Our study shows that, even in muddy systems, the material into which a fluvial surface scours is likely to have sufficient quality to permit reservoir communication.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas