Atlas of Cretaceous gas fields, Piceance Basin, northwest Colorado

Nathan Rogers, Stephen Cumella, Paul Weimer, and Mike Leibovitz

The Cretaceous gas fields in the Piceance Basin can be classified by geographic area, as well as by key geologic criteria, including producing interval of the Mesaverde, thickness and stratigraphic position of Mesaverde coals, maturity level of Mesaverde coals, and relative contribution of Mesaverde coals versus Mancos Shale gas source. Most gas production in the Piceance to date has been from Grand Valley, Parachute, Rulison, and Mamm Creek fields, which are located along the Colorado River valley, where topography and infrastructure has been favorable. Almost all production in these fields has been from a continuously gas-saturated interval of fluvial sands the Williams Fork Formation that ranges from about 1800-2400 ft in thickness. Water production is low, typically 5-10 BW/MMCF. Gas production from the marine sandstones of the Iles in these fields is minor; higher water production from the Iles negatively impacts the production economics. In the northern part of the Piceance Basin, most production is also from the Williams Fork, but the lower Mesaverde (Iles and Sego formations) contains more proximal facies than the time-equivalent intervals to the south, and this interval can contain a significant portion of the reserves in some wells. The northern Piceance is structurally deeper, and as a result, drill depths are typically >3000 ft deeper than the southern Piceance. The Williams Fork gas-saturated interval is generally thicker in the northern Piceance (>3000 ft), but the local thickness variation of the gas-saturated interval is much greater. Water production in the northern Piceance is in general much higher, with values in the 10's to 100's of BW/MMCF. Mesaverde coal thicknesses are greater in the southern Piceance, especially in the southeastern Piceance, and the gas source from coal is correspondingly greater. The northern Piceance contains coals in the upper Williams Fork that are not present in equivalent strata to the south. These stratigraphically shallower coals, which are mature due to their deeper burial, probably play a significant role in creating the thicker gas columns in the northern Piceance. Recent for Mancos/Niobrara shale-gas drilling gas has revealed a previously unrecognized tremendous gas resource with the potential of 10's of TCF's of gas. Recent geochemical studies have indicated that gas sourced in the Mancos/Niobrara may have contributed a significant amount of the gas produced from the Mesaverde.

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012