498 



UNITED STATES MINERAL RESOURCES 



1961, principally in Scotland, Estonia (U.S.S.R.), 

 and Manchuria (China) . Oil-shale deposits in France, 

 Sweden, Germany, Spain, South Africa, and Aus- 

 tralia have also been mined on a modest scale, and 

 a new shale-oil operation is scheduled to begin in 

 1972 in Brazil. 



In the United States, experiments in the produc- 

 tion of oil and gas from oil shale have been con- 

 ducted since 1850. Most early experiments were 

 brief, ineffective efforts, but since 1944 pilot plants 

 have been intermittently operated either by the U.S. 

 Bureau of Mines (1944-56) or by private industry 

 (1957-72) in the western Colorado oil-shale deposits. 

 These pilot plants retorted oil shale that had been 

 mined underground by conventional methods. In 

 1966, the U.S. Bureau of Mines estimated the cost of 

 producing shale oil by this method at about $3 a bar- 

 rel (Schramm, 1970, p. 192). In 1970, the National 

 Petroleum Council (1972) also evaluated this method 

 and estimated that each barrel of oil with a heat 

 value of 5.4 million Btu would cost between $4.30 and 

 $5.30 at the plant site. This estimate assumed a plant 

 producing 100,000 barrels of oil a day (initial invest- 

 ment of $500 million) that used only the richer, more 

 accessible oil shale (oil shale yielding 30-35 gallons 

 of oil per ton, in zones more than 30 feet thick, with- 

 in 1,500 ft of the surface) . This cost compares un- 

 favorably with the present price of crude oil, which 

 is about $3.50 a barrel. It is probable, however, that 

 the value of coproducts of shale oil, such as aluminum 

 or sodium bicarbonate, or advancements in technolo- 

 gy, or increases in the price of crude oil, will make 

 shale oil competitive with crude oil in the near 

 future. 



The possibility of heating the oil shale under- 

 ground and pumping the oil to surface (in situ re- 

 torting) has been investigated by private industry 

 in western Colorado, and by the U.S. Bureau of 

 Mines in southwest Wyoming (Schramm, 1970, p. 

 188) . Many technical problems remain to be solved, 

 but this method holds promise as a way to obtain the 

 oil with little harm to the environment. 



Synthetic gas can be produced from oil shale, but 

 the cost of converting the organic matter to high- 

 quality gas suitable for mixing with natural pipeline 

 gas would appear to be greater per unit of contained 

 energy. For example, it would cost $0.50 per million 

 Btu to convert oil to gas. 



OIL-SHALE DEPOSITS IN THE UNITED STATES 



Oil shale occurs in many parts of the country in 

 rocks ranging in age from Ordovician to Tertiary. 

 Oil-shale deposits can be divided into three types — 



shale in lacustrine rocks, marine shales, and the 

 shales associated with coal beds. 



LACUSTRINE OIL-SHALE DEPOSITS 



The principal oil-shale deposit of lacustrine origin 

 is in the Green River Formation of Eocene age, 

 which underlies about 17,000 square miles in Colo- 

 rado, Utah, and Wyoming. Other small lacustrine 

 deposits of Tertiary age containing oil shale have 

 been reported in the intermontane basins of Mon- 

 tana, Nevada, Idaho, and California, but they remain 

 unexplored. 



The Green River Formation consists of oil shale 

 interbedded with varying amounts of tuff, siltstone, 

 sandstone, claystone, and locally with halite, trona, 

 or nahcolite. The formation ranges in maximum 

 thickness from a few feet to several thousand feet 

 and intertongues laterally with the predominantly 

 fluvial beds of the Wasatch Formation. The Green 

 River Formation was originally deposited principal- 

 ly from two large Eocene lakes, one lying south of 

 the Uinta Mountains and the other lying north and 

 east. It is now preserved in seven basins — the Uinta 

 Basin in Utah, the Piceance Creek and Sand Wash 

 basins in Colorado, and the Green River, Great Di- 

 vide, Washakie, and Fossil basins of Wyoming. 



In the Piceance Creek deposit (Donnell and Blair, 

 1970; Donnell, 1961), the Parachute Creek Member 

 of the Green River contains up to 2,000 feet of oil 

 shale in alternating rich and lean beds. Some of these 

 rich beds are very persistent; the Mahogany zone, 

 for example, underlies more than 2,000 square miles 

 in Colorado and Utah. The oil shale is thickest and 

 richest in the north-central part of the Piceance 

 Creek basin, where it also contains nodules, lenses, 

 and beds of nahcolite (NaHCOs) and halite (NaCl), 

 and disseminated crystals of dawsonite [NaAl (OH2) 

 CO3]. Nahcolite is potentially valuable as a source of 

 sodium carbonate or sodium bicarbonate, and daw- 

 sonite as a source of aluminum. Toward the margins 

 of the basin, the oil-shale sequence becomes progres- 

 sively thinner and leaner, intertonguing with sand- 

 stone and siltstone. 



In the Uinta Basin (Cashion, 1967), the Green 

 River Formation is similar to that in the Piceance 

 Creek basin, but the oil-shale sequence is thinner and 

 leaner and does not contain significant amounts of 

 saline minerals. In the Green River Basin, oil shale 

 occurs in thin, but widespread units in the Tipton 

 Shale, Wilkins Peak, and Laney Members of the 

 Green River (Culbertson, 1972; Bradley, 1964). The 

 Wilkins Peak Member locally contains thick beds of 

 trona (Na2C03'NaHC03'2H20) and halite, and dis- 

 seminated crystals of shortite (Na2C03*2CaC03), 



