Julia Caldaro-Baird¹, Andrew Pulham², Paul L. Kovach³

(1) Texaco E & P, Denver, CO
(2) University of Colorado, Boulder, CO
(3) Barrett Resources Corporation, Denver

ABSTRACT: Lithofacies Interpretation from Core Studies of the Almond Sandstone at Stagecoach Draw Field, SW Wyoming

The Upper Cretaceous Almond Formation is the primary producing formation at Stagecoach Draw field, southwestern Wyoming. To assist in field development, reservoir characterization studies and detailed core analysis were performed through a cooperative program between Texaco E & P, Inc. and the University of Colorado. An extensive coring program was undertaken during the 1993-1998 drilling programs to provide the foundation for these studies. The Almond Formation at Stagecoach Draw is a single westward thinning sandstone body that produces in a combined structural and stratigraphic trap setting. The field helps to delineate the furthest landward Almond deposition in the final transgression of the Lewis Seaway. Detailed facies analyses of the cores reveal seventeen lithofacies, which can be grouped into five facies associations. These facies associations are indicators of predicted reservoir quality. Subenvironments represented include tidal channel, lagoonal, estuarine, tidal delta, and marsh/swamp facies. From these facies assemblages, a depositional model was constructed. Facies analysis and well log interpretation reveal that these facies were deposited in what appears to be three pulses of high frequency sea level rise and fall. Interpretation of key surfaces is complex in this back barrier setting due to the ongoing autocyclic depositional processes concurrent with relative sea level processes during deposition. The three sandstone divisions are identified where by finer grained, bioturbated "zones" correspond to slight gamma-ray shifts. These divisions are correlated around the field and may represent high frequency sequences

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado