Stratigraphic Architecture and Connectivity of High-Sinuosity Fluvial Sandstone Bodies in Coal Canyon, Colorado with Subsurface Comparison to Grand Valley Field
This study addresses the reservoir-scale stratigraphic architecture and connectivity of fluvial deposits of the lower Williams Fork Formation through analysis of outcrop analogs in Coal Canyon, Colorado with comparison to equivalent deposits at Grand Valley Field, Piceance Basin, Colorado.
The field locality in Coal Canyon, informally called Hoodoo Hill, is located approximately 2.2 miles (3.5 km) north of Palisade, Colorado and provides three-dimensional outcrops of fluvial sandstone geobodies in the lower 300 ft (91 m) of the Williams Fork Formation (Cameo interval). The study site is approximately 2500 ft (762 m) long (east-west), 1500 ft (457 m) wide and has a total surface area of approximately 115 acres (0.47 km2). The Rollins Sandstone Member of Iles Formation crops out on the south flank of the hill. At Hoodoo Hill, analysis of sandstone-body type, thickness, stratigraphic distribution, geometry, sedimentary structures, and grain size reveals several high net-to-gross ratio intervals of multistory/multilateral channel sandstones, with complex stacking of individual bodies, multiple scour surfaces, and lag gravels that could be barriers to fluid flow. Most of Hoodoo Hill is comprised of low net-to-gross ratio intervals that are dominantly floodplain mudrocks with isolated point bars and few crevasse splays. Lithofacies relationships within the sandstone bodies are highly variable (changes within tens of feet). To investigate the distribution and connectivity of the reservoir-quality sandstone bodies, three-dimensional outcrop models were constructed. The models and associated sandstone-body connectivity analysis show that connectivity varies stratigraphically.
The outcrop-derived data from Hoodoo Hill were compared to equivalent deposits of the lower Williams Fork Formation at Grand Valley Field. Outcrop observations and borehole images were used to establish criteria to define electrofacies in the subsurface. Sandstone bodies were classified by type and correlated between wells. Similar to observations from outcrop, the fluvial deposits have a complex internal architecture, are generally isolated in low net-to-gross ratio intervals, but, in some cases, appear connected at 10-acre spacing.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009