Regional subsurface stratigraphy of the Piceance Basin, northwest Colorado: results of a joint RPSEA-industry sponsored research program

Paul Weimer, Dag Nummedal, Stephen Cumella, Mike Leibovitz, Renee Foster, Kristopher Schwendeman, Dawn Tschanz, Joseph Nicollette, Nathan Rogers, Renaud Bouroullec, and Edmund (Gus) Gustason

A regional subsurface evaluation of the Piceance Basin was undertaken as part of a joint RPSEA and industry sponsored research project. Wireline logs from more than 6000 wells and 600 km of 2D seismic data were interpreted. This data base provided us the opportunity to evaluate the regional stratigraphic relationships at a scale and detail not previously available. About 120 stratigraphic tops were defined between the top Dakota Group and top Wasatch Formation, and were correlated regionally to sub-regionally in the basin. Major new conclusions were the following: (1) The Mancos and related intervals are divided into three broad intervals: lower Mancos, Niobrara and equivalent intervals, and upper Mancos. (2) The thick overall progradational shoreline units (Castlegate through Rollins) were correlated, in great detail, and distinct shoreline trends could be defined. (3) Deposition of the Cameo and related coal units (lower Williams Fork Formation) are coeval to the Rollins shorelines and were correlated with detail. The most regional pervasive coals are present in the lower William Fork interval 1 associated with the extensive progradation of the Rollins shoreline. Major coal deposition was tied to times of discrete aggradation in the shorelines. (4) The middle Williams Fork is the major producing reservoir facies along the Colorado River fields. A distinct fluvial architecture and stacking pattern can be related to the sequence stratigraphic framework: vertically, the unit evolves from isolated, single-story fluvial channels to stacked isolated channels (late HST), overlain by multi-story, amalgamated laterally continuous channels. (5) The upper Williams Fork comprises several units. To the south, this unit is the seal in the fields along the Colorado River. To the north is a facies change to lower coastal plain strata. A northwest striking fault in the central western portion of the basin impacted the middle and upper Williams Fork: (1) it controlled the amount of incision of the middle Williams Fork incised valley, with incision decreasing markedly to the east where the valley crosses the fault; and (2) the updip pinchout of the Price Coal in the upper Williams Fork corresponds to the trace of the fault. (6) The lower Tertiary Wasatch Formation is divided into 12 intervals. The four lower intervals are primarily interbedded fluvial sandstones, and overbank mudrock; interval 6 includes the producing G sandstone.

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