Wyoming Geological Association: 1982 Luncheon Meetings Casper, Wyoming: Abstracts of Papers

The Anschutz Ranch East field, the giant of the western United States Overthrust Belt, had its beginning as a more humble-sized project. It is a retrograde condensate accumulation in the Jurassic Nugget Formation discovered by the Amoco Bountiful Livestock No. 1, completed December 31, 1979. Production here is the deepest along the Cretaceoussourced liquids trend which extends southwestward from Ryckman Creek field to Pineview field. The field, situated in the extreme southwest corner of Wyoming and adjacent to Utah, consists of separate reservoirs in two en echelon structures. The west lobe is a highly overturned, narrow anticline with over 2,000 ft (610 m) of hydrocarbon column. The east structure, producing from two wells, is poorly defined structurally, but appears to be an elongate anticline separated from the west lobe by a largely unfaulted, overturned syncline. The eastern extent of the reservoir is believed to be the Nugget truncation against the regionally important Absaroka thrust plane. Conventional seismic is inadequate to map the field for development purposes, but newly acquired 3-D coverage has yielded positive preliminary results. The Nugget sandstone averages 1,100 ft (335 m) in thickness and is largely aeolian in origin, with interpreted dune sets and interdunal areas commonly distinguishable using log suites. Matrix characteristics without extensive fracturing probably account for the high producibilities. The field is currently essentially shut-in pending ratification of the Development Unit Agreement and subsequent start up of the pressure-maintenance program.