Analysis and Modeling of Fluvial Sandstone-Body Architecture and Heterogeneity in the Cameo Interval of the Lower Williams Fork Formation in Coal Canyon, Southwestern Piceance Basin, Colorado
Multiple scales of heterogeneity are associated with fluvial (and shallow marine) reservoirs of the lower Williams Fork Formation within the Piceance Basin. Well-exposed outcrops of these strata in the southwestern Piceance Basin have been used to address the stratigraphic and sedimentological controls on reservoir heterogeneity.
"Hoodoo Hill", located approximately 2.2 miles northwest of Palisade, Colorado, provides “reservoir-scale” three-dimensional outcrops of fluvial sandstone geobodies in the lower 300 ft of the Williams Fork Formation (Cameo interval). The study site is approximately 2,500 ft long (east-west), 1,500 ft wide and has a total surface area of approximately 115 acres. The Rollins Sandstone Member of Iles Formation crops out on the south flank of the hill. Locations of 63 geobodies were defined by GPS mapping and 13 measured sections. Based on sedimentologic characteristics, the geobodies were classified into three types: single-story channel bodies, multistory/multilateral channel bodies, and splays. Single-story channel bodies (N = 18) range in thickness from 2.6 to 12.6 ft and average 7.2 ft, whereas the apparent-width values range from 44 to 1,700 ft, and average 439 ft. Multistory/multilateral channel bodies (N = 18) range in thickness from 4.5 to 24.9 ft and average 11.9 ft; the apparent-width values range from 140 to 2,071 ft, and average 748 ft. Splay geobodies (N = 27) range in thickness from 1.1 to 5.5 ft (average = 2.8 ft), and in apparent width from 42 to 843 ft (average = 248 ft).
To investigate the distribution and associated connectivity of the reservoir-quality sandstone bodies, three-dimensional outcrop models were constructed. The models are constrained to measured sections, dimensional statistics, net-to-gross ratios, sandstone-body percentages, spatial trends, and other data acquired directly from outcrop and with sandstone-body objects that most closely resemble those in the outcrop. Given the uncertainty in the sandstone-body apparent-width values and the range of paleocurrent values for each channel body, the sandstone bodies were analyzed to produce a range of possible width values for modeling. The models were analyzed for static sandstone-body connectivity using several well spacings (40-, 20-, 10-, “10-infill”, 5-acre). The models and associated sandstone-body connectivity analyses show how connectivity varies stratigraphically and with net-to-gross ratio.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009