--> ABSTRACT: Delineation of Stratigraphic Heterogeneities in the Arch Unit, Wyoming Based on an Outcrop Analog, by Hisham A. Al-Siyabi, Roger M. Slatt; #91020 (1995).

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Delineation of Stratigraphic Heterogeneities in the Arch Unit, Wyoming Based on an Outcrop Analog

Hisham A. Al-Siyabi, Roger M. Slatt

The Arch Unit, part of Patrick Draw field, Wyoming, produces oil and gas from the late Cretaceous upper Almond interval. The interval is comprised of two sandstone bodies, the UA5 and UA6. These two sandstones appear generally uniform on well logs. In this study the UA5 and UA6 are recognized to be more stratigraphically complex than previously thought. These complexities were recognized by detailed description of an outcrop analog in the Rock Springs area, 22 miles south of the Arch Unit. Recognition of these complexities and their characteristics can be useful for improved reservoir management in this and other Almond reservoirs.

The outcrop comprises a barrier island depositional system with several component facies. Tidal inlet facies are comprised of channel floor, active channel fill and spit platform sediments. Channel floor sediments are lag dominated, while the fining upward active channel fill sediments are comprised of mud draped trough cross beds. The coarsening upward spit platform sediments are composed of multiple lateral accretion beds that vary in length and thickness. Tidal flat facies occur as coarsening upward cycles of mud, mixed and sand flat sediments. Lenticular bedding dominates the mud flats, while wavy bedding occurs in the mixed flats and the sand flats are ripple cross stratified.

A tidal inlet dominated barrier island depositional system comprises the Arch Unit. The UA5 is comprised of tidal inlet facies similar to those found in outcrop. The UA6 is comprised of tidal flat facies, also similar to those seen in outcrops. Channel fill and spit platform sediments make the tidal inlet facies, while tidal flat facies are composed of mud, mixed, and sand flat sediments.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995