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Occurrence and Distribution of the Almond Formation in Portions of the Sand Wash Basin, Northwestern Colorado

Schutt, DeLonna F. 1, John B. Curtis2, Donna Anderson2 (1) Kerr- McGee Rocky Mountain Corporation, Denver, CO (2) Colorado School of Mines, Golden, CO

 

The Upper Cretaceous Almond Formation in northwestern Colorado was deposited during the third transgressive-regressive cycle of the North American Western Interior Cretaceous Seaway. The Almond Formation is the transgressive portion of the cycle and the Lewis Shale is the regressive portion of the cycle.

 

The study area, located entirely in Moffat County, Colorado, covered approximately 2,500 mi2 of the Sand Wash basin. The purpose of the study was to indicate whether the Almond Formation has future hydrocarbon potential. Our data set included 4 cores, 2 outcrop locations, 80 well logs, and 47 production tests.

 

Facies were defined from the cores, and depositional environments interpreted. The core facies were correlated to facies observed in outcrop. The Almond Formation is a shallow marginal-marine facies tract with an estuarine component and a coastal plain component.

 

A network of 17 stratigraphic cross sections was constructed which showed the back-stepping nature of the Almond Formation from east to west. Electrofacies were defined from the well-log curves and used to characterize the coarsening-upward character of the Almond Formation. Isopach maps were then generated showing the thickness of the Almond Formation and the thickness of the interval between the Asquith Marker of the Lewis Shale and the Almond Formation. An apparent vertical stacking of shorelines could be seen on the western side of the basin. Thin section analysis gave insight into reservoir quality of the lithic arenites identified in the formation.

 

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana