Sedimentology and Reservoir Potential of Allochthonous Upper Desert Creek Carbonates, Southern Margin of the Aneth Complex (Middle Pennsylvanian), Paradox Basin, Utah

Abstract

The Aneth Field in the Paradox Basin (SE Utah) has produced nearly 500 MMbbls of oil from phylloid-algal and oolitic carbonate reservoirs of the lower and upper Desert Creek (Middle Pennsylvanian) sequences, respectively. This study explores a third DC facies with reservoir potential that has been understudied to this point. Over much of the 144 square-mile field, the lower and upper Desert Creek sequences are approximately 100 feet thick. On the south margin of the buildup, however, isopach maps show a significant thickening (150 feet) of the upper DC resulting from offshore transport of carbonate debris off the leeward (southern) margin of the complex. Northsouth- oriented stratigraphic panels constructed from log and core data permit characterization of thickness and facies trends through the upper DC thickens from banktop (north) to distal basin (south). Highstand shedding emplaced basinward thinning and fining wedges of dark-gray, mud-dominated packstone and wackestone deposits. Facies range from proximal rudstone and floatstone to thin, graded distal turbidites. The latter extend at least 12 miles into the basin. Many core horizons are oil-stained and relatively rich in organic material (TOC studies in process). Certain core intervals are characterized by the presence of oil-expulsion fractures that permitted hydrocarbons to migrate updip from TOC-rich distal facies into the granier rocks of the Aneth complex. The wedge of allochthonous carbonates is underlain by lowstand evaporites associated with salt cycle 4 and sealed on top by lowstand evaporites of salt cycle 3. This study highlights a facies succession that has been greatly understudied in the Aneth Field and represents a potential new unconventional play in addition to the traditional oolitic upper Desert Creek play.

AAPG Datapages/Search and Discovery Article #90357 ©2019 AAPG Rocky Mountain Section Meeting, Cheyenne, Wyoming, September 15-18, 2019