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Abstract

Five depositional facies occur in five oriented cores obtained from the Bartlesville Sandstone (Cherokee Group, Middle Pennsylvanian) in the Madison Unit “B” enhanced recovery pilot project in Greenwood County, Kansas. By orienting the cores and studying the flow directions determined from high-angle crossbedding, a model for predicting the trend of the channel sandstone was constructed. Environments of deposition associated with the channels are (1) lnterdistributary Bay Siltstone, Shale, and Sandstone Facies; (2) Crevasse Splay Sandstone and Siltstone Facies; (3) Overbank Shale and Siltstone Facies; (4) Distributary Channel Sandstone Facies; and (5) Delta Plain Shale and Siltstone Facies.

These facies may be recognized on gamma-ray logs as well as on permeability and grain-size plots. The Distributary Channel Facies is the major reservoir facies and overlies brackish to continental delta plain sediments. It is overlain by brackish and marine facies, including overbank and interdistributary bay shales and siltstones. The channel had low sinuousity, as is evident from the narrow trend of the sandstone and the blocky (rather than “bell-shape”) nature of the gamma-ray log. An overall fining-upward sequence typical of fluvial-deltaic sediments is suggested by an upward decrease in the grain size, a decrease in the scale of sedimentary structures, and an increase in the amount of interstitial clay matrix.

Variations among the sandstone facies are also reflected by variations in permeability values. Controls on permeability that differ among the various facies are packing, the presence of ductile rock fragments, the amount and morphology of authigenic and detrital clay, and sorting. The permeability of the Distributary Channel Facies decreases from 60 to 100 md in trough crossbedded sandstones typical of the lower and middle part of the channel fill to 20 to 60 md in rippled sandstones, siltstones, and shales of the upper part of the channel. Low permeability values (0-20 md) are characteristic of facies composed primarily of siltstone and shale.

The Distributary Channel Facies is continuous across the project area and its thickness varies in a predictable manner. Numerous and detailed dip directions measured primarily in trough crossbeds in four of the five oriented cores that were used in the study indicate that the channel flowed in a west-southwesterly direction across the project area. This flow direction is parallel to the maximum elongation direction of the sand body. The Overbank, Crevasse Splay, and Interdistributary Bay Facies are not continuous across the whole project area. These facies filled the topographically low areas adjacent to the channel.

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