--> Abstract: Anatomy of a Fluvial Sandstone: The Salt Wash Member of the Morrison Formation in Southern Utah, by J. W. Robinson and P. J. Mccabe; #91012 (1992).

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ABSTRACT: Anatomy of a Fluvial Sandstone: The Salt Wash Member of the Morrison Formation in Southern Utah

ROBINSON, JOHN W., Colorado School of Mines, Golden, CO, and PETER J. MCCABE, U.S. Geological Survey, Denver, CO

The 150 m thick Salt Wash Member of the Morrison Formation (Jurassic) is well exposed over an area of 1000 sq. kilometers in the southern Henry Mountains of Utah and is interpreted as the deposit of a braided stream system that prograded toward the northeast. A comprehensive understanding of the fluvial facies in three dimensions has been gained by integrating data from photomosaics, stratigraphic sections, well logs, petrography, and minipermeameter analyses.

Over 90% of the Salt Wash Member consists of sandstones, the majority of which are trough cross-bedded. These sandstones have an overall coarsening-upward trend through the unit, with very fine grained quartz-rich beds at the base and chert granule and pebble conglomeratic sandstones toward the top. The sandstones form fining-upward units, 1 to 5 m thick, that are laterally extensive over tens of meters and are separated by discontinuous, 0.01 to 1 m thick mudstone drapes and/or mudstone intraclast lags. Fining-upward units amalgamate to form sandstone sheets that are up to 20 m thick and from 100 m to 2 km wide. Sandstone sheets have flat bases and tops and are separated by rooted mudrock units generally less than 3 m thick. Minipermeameter data from outcrop and core average 600 md i trough cross-bedded and massive sandstones, 200 md in horizontal laminated sandstones, and <50 md in fine-grained deposits.

Conclusions from our study could be used to better model flow unit continuity from field-spaced well data in fluvial reservoirs with high net to gross reservoir sandstone ratios. Mudrock units divide a reservoir into flow-unit compartments on various scales, influencing fluid migration and drainage. An understanding of the scale of such discontinuities will aid in better reservoir production development.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)