Basin-scale Sequence Stratigraphy and Distribution of Depositional and Mechanical Units in the middle and upper Williams Fork Formations, Piceance Basin, Colorado

Michele Wiechman
Colorado School of Mines, Department of Geological Engineering and Geology Golden, Colorado
[email protected]

The Piceance Basin, northwest Colorado, is home to one of the most important basin-centered tight-gas accumulations in North American. A wide range of geologic controls are responsible for the variation in gas production from the heterogeneous, low permeability reservoirs here, but these controls are not well understood. Outcrop-to-subsurface stratigraphic correlation and detailed analysis of facies can elucidate potential stratigraphic controls on geographic and stratigraphic zones with better gas production. The dataset consists of 12 stratigraphic profiles, >100 well-logs and 9 outcrop gamma-ray profile curves. Depositional environments are recorded by 31 lithofacies and revel facies diversity contributing to reservoir heterogeneity. Lithofacies are interpreted as high-sinuosity, meandering fluvial; isolated, low-sinuosity anastomosed fluvial; tidally influenced fluvial; estuarine; regressive marine shoreline; and transgressive marine shoreline barrier systems. Facies interpretations suggest an overall stratigraphic trend from fluvial/flood plain depositional environments in the lower part to a coastal plain/estuarine and marine shoreface in the middle, and back to a fluvial depositional environment. Fluvial facies are laterally extensive with variations in channel type throughout the basin. Marine and tidal facies show lateral discontinuity in the western sections of the basin. Regional correlations through the middle and upper Williams Fork show a strong geographic, as well as stratigraphic partitioning of facies within a single stratigraphic unit. Potentially higher reservoir quality was identified in 4 lithofacies in (1) marine shoreface, (2) meandering fluvial, (3) anastomosed fluvial, and (4) tidally influenced deposits. These facies demonstrate varying facture intensity with the anastomosed and marine shoreline facies showing the most intense fracturing.

AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects