Analysis of Fluvial Sandbody Characteristics and Connectivity in a High Net-to-Gross System, Upper Williams Fork Formation, Plateau Creek Canyon, Piceance Basin, Colorado

Quentin German¹, Matthew Pranter¹, and Rex D. Cole^2
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, western Colorado, are important analog to analyze sand-body characteristics and connectivity in a high net-to-gross fluvial system. These outcrops are used to assess sub-seismic variability in fluvial sand-body type, dimension, geometry, and distribution based on aerial lidar, orthophotography, digital photomosaics, measured sections, and behind-the-outcrop cores. Sand-bodies include single to multiple-story channel complexes with dimensions ranging from 0.5-30 ft (0.15-9 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. Amalgamation is common in this high net-to-gross system, however, thin laterally extensive interbedded shales exist that could vertically compartmentalize sand-bodies at the reservoir scale. Core plug porosity and permeability for the fluvial sandstones from a behind-the-outcrop core range from 2 to 27% (mean=18.7%) and 0.001 to 2000 md (mean=242 md), respectively. Photomosaics, measured sections, core, and lidar data are used to define fluvial elements, facies variations, bed boundaries, and sand-body dimensions. These data are used to build and condition 3-D geologic models of the deposits in order to explore the affects of sandstone distribution, stacking patterns, and amalgamation on static sand-body connectivity.