Abstract

The Uintah and Ouray Indian Reservation, located in northeastern Utah, lies within the Uinta Basin, a structural and depositional basin of Tertiary age. During Eocene time a thick sequence of kerogen-rich sediments accumulated along the trough of a lake that occupied the basin area. Those endurated sediments comprise the oil-shale zones of the Green River Formation and much of the reservation is underlain by one or more of the zones. The richest of the oil-shale zones, the Mahogany zone, is deeply buried where it is best developed within the reservation (northern part) and crops out where the oil-shale grade is much lower, in the southern part of the reservation. Total oil-shale resources of the Mahogany zone within the reservation cannot be accurately determined due to the scarcity of core hole data, however, assay data from core holes adjacent to the eastern part of the reservation allow an estimate of the inferred resources of the Mahogany zone in apart of the reservation. The easternmost part of the reservation is estimated to contain 10 billion barrels of shale oil in that part of the Mahogany zone that yields 25 gallons of oil per ton, is at least 25 ft (7.6 m) thick, and is overlain by less than 3,000 ft (914 m) of overburden.