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Thomas C. Chidsey1, David E. Eby2
(1) Utah Geological Survey, Salt Lake City, UT
(2) Eby Petrography & Consulting, Inc, Littleton, CO

Abstract: Facies of the Paradox Formation, Southeastern Utah, and modern analogs: Tools for exploration and development

Over 400 million bbls of oil have been produced from shallow-shelf carbonate buildups in the Desert Creek zone of the Pennsylvanian (Desmoinesian) Paradox Formation in the circum-Aneth area of the Paradox basin. These buildups were deposited in very different depositional environments in spite of their proximity to each other. Our study first described the depositional settings of various producing fields and determined their modern analogs, and then mapped regional facies belts. Understanding these facies and depositional patterns within the basin helped to: (1) estimate reservoir heterogeneity and capacity, and (2) identify areas that have the greatest petroleum potential.

We recognize three regional facies belts from our evaluation of case-study fields, cores from exploratory wells, and modern analogs: (1) open-marine, (2) shallow-shelf /shelf-margin, and (3) intra-shelf/salinity-restricted facies. The open-marine facies belt includes carbonate buildups (typically crinoid-rich mounds), carbonate and euxinic black muds, wall complexes, and detrital fans. The shallow-shelf/shelf-margin facies belt includes carbonate buildups (mounds), calcarenites (beach and stabilized grain flats), and platform-interior carbonate muds and sands. The intra-shelf/salinity-restricted facies belt represents small subbasins within the shallow-shelf/shelf-margin facies belt, and includes evaporites, tidal-flat muds, bioclastic lagoonal muds, tidal-channel carbonate sands and stromatolites, and euxinic dolomites.

The results of this study were valuable in developing geostatistical models and compositional reservoir simulations to predict field performances under CO2-flooding and waterflooding recovery processes.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana