--> ABSTRACT: Improving Recovery Efficiency through Detailed Mapping of Compound Valley Fills, Morrow Formation, Cheyenne County, Colorado, and Wallace County, Kansas, by Beverly A. Blakeney; #91003 (1990).

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ABSTRACT: Improving Recovery Efficiency through Detailed Mapping of Compound Valley Fills, Morrow Formation, Cheyenne County, Colorado, and Wallace County, Kansas

Beverly A. Blakeney

The Morrow sandstone in the State Line trend, Cheyenne County, Colorado, and Wallace County, Kansas, was originally mapped as a continuous and homogeneous reservoir. The plan of depletion for the field and reservoir modeling were initially based on this hypothesis. However, anomalous pressure data and fluid contacts could not be explained under the homogeneous reservoir model.

Core facies and log analyses document multiple valleys that incise into each other. These valleys and their respective sandy valley fills can be mapped. The multiple scours result in complex spatial relationships of reservoir bodies that can cause either isolation of the reservoirs or allow pressure communication between them. Reservoir quality differs among valleys and within individual valley fills, which greatly affects productivity. Estuarine valley fills are composed of fine, low permeability sand (0.1-100 md). In contrast, high-energy channel fills are composed of coarse, high permeability sand (0.5-12 d). The two facies may be juxtaposed because of valley incision or may grade laterally into each other along the axis of one valley. Variable reservoir quality and the compound na ure of the Morrow reservoirs cause heterogeneity that can reduce recovery efficiency.

Mapping of previously unrecognized subdivisions of the reservoir is critical to efficient reservoir management. New gas and water injection wells were proposed after the compound valley fill model was integrated with the original plan of depletion. Incremental ultimate recoveries may be enhanced in excess of 8 million bbl of oil through this effort.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990