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.