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Analysis
of Fluvial Sand-Body Characteristics and
Dimensions in a High Net-to-Gross System, Upper Williams Fork Formation, Main
and Plateau Creek Canyons , Piceance Basin, Colorado
Sommer, Nicholas1, Quentin German1, Matthew Pranter1, Rex D. Cole2 (1) University of Colorado, Boulder, CO (2) Mesa State College, Grand Junction, CO
Outcrops of the Upper Williams Fork Formation exposed in
Plateau Creek Canyon and Main Canyon, western Colorado, are important analogs to
analyze sand-body dimensions, distributions, characteristics, and architecture
in a high net-to-gross fluvial system. These outcrops provide information on
sub-seismic variability of fluvial sand bodies based on aerial liar and
orthophotography, digital photomosaics, measured sections, and
behind-the-outcrop cores. Sand-bodies are associated with single- to
multiple-story channel complexes with dimensions ranging from 0.5-35 ft (0.15-11
m) in thickness (or composite thickness) and 20-3000 ft (6-914 m) in apparent
width. Single-story sand bodies are tabular to lenticular in cross section and
often have prominent basal-scour surfaces. Due to the braided depositional
style, amalgamation is common in this high net-to-gross system, however, thin
laterally extensive interbedded shales and siltstones exist that could
vertically compartmentalize sand-bodies at the reservoir scale. Ten square miles
of high-resolution aerial liar and corresponding geo-referenced digital
orthophotos (1.5 ft / 0.5 m resolution) were acquired in both canyons. Merged
liar scans and orthophotos are interpreted in a 3-D interactive computer
environment and permit detailed dimensions and other attributes of fluvial sand
bodies to be measured. Photomosaics, measured sections, behind-the-outcrop
cores, and liar data are used to define fluvial elements, facies variations, bed
boundaries, and sand-body dimensions. These data are essential inputs to build
and condition 3-D geologic models of these and similar deposits.
AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section
Meeting, Billings, Montana