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