Fluvial Sandstone-Body Dimensions and Reservoir Connectivity within a Meandering to Braided System: An Example From the Williams Fork Formation, Piceance Basin, Colorado

Pranter, Matthew J.¹, Henrikus Panjaitan², Quentin A. German¹, Zulfiquar A. Reza¹, Rex D. Cole³, Neil F. Hurley², Donna S. Anderson² (1) University of Colorado, Boulder, CO (2) Colorado School of Mines, Golden, CO (3) Mesa State College, Grand Junction, CO

Fluvial sandstone-body dimensions and connectivity are analyzed using outcrops of the Williams Fork Formation in Coal and Plateau Creek Canyons, Piceance Basin, Colorado. The exposures are stratigraphically analogous to the undifferentiated interval of the Williams Fork Formation in the subsurface that forms petroleum reservoirs within the Piceance Basin. The sandstone-body characteristics are evaluated using high-resolution aerial LiDAR, digital orthophotographs, photomosaics, behind-outcrop cores, nearby well logs, and field measurements. Based on sandstone-body statistics and various reservoir scenarios, connected sandstone-body volume, number of connected geobodies and sandstone bodies, connected thickness, and other connectivity parameters are evaluated.

Sandstone-bodies in the Lower Williams Fork (meandering-stream system) are grouped into 3 types for this analysis: single-story-channel-fill, multistory-channel-fill, and crevasse-splay deposits. Of 633 sandstone bodies measured in Coal Canyon (based on LiDAR data), there are 109 single-story channels, 258 multistory channels, and 266 crevasse-splay bodies. Single-story channel sandstones range in thickness from 4-21 ft. Multistory-channel and crevasse-splay sandstones are 4.5-32.5 ft and 0.5-6.5 ft thick, respectively. Single- and multistory-channel sandstone-body widths range from 46-894 ft and 38-2553 ft, respectively.

The Upper Williams Fork in Plateau Creek Canyon (low-sinuosity braided system) is characterized by sheet-like sandstones and associated mudrocks. Based on 113 measurements, sandstone bodies include single-story channels to multistory-channel complexes with dimensions ranging from 1-54 ft in thickness (or composite thickness) and 204-2565 ft in apparent width, with an average width-to-thickness ratio (W:T) of 34:1. Amalgamation of sandstone bodies is common; however, thin laterally extensive interbedded mudrocks exist that could compartmentalize sandstones at the reservoir scale.