502 



UNITED STATES MINERAL RESOURCES 



The United States is calculated to contain about 

 2.4 million cubic miles of sedimentary rocks to a 

 depth of 20,000 feet, of which 0.5 percent is assumed 

 to be shale containing 10-65 percent organic matter 

 and yielding 10-100 gallons of oil per ton. The total 

 yield of oil is calculated to be about 28 trillion bar- 

 rels, of which about 5 percent is assumed to be from 

 shale yielding 25-100 gallons of oil per ton. From 

 these figures are subtracted the identified and hypo- 

 thetical resources to obtain the speculative resources. 

 Similar calculations were made to obtain the specu- 

 lative resource figures shown in table 96. 



Marine black shales are the primary source of the 

 speculative shale-oil resources because they occur in 

 large volumes in sedimentary basins all over the 

 United States. Ordovician shales in New York, Illi- 

 nois, Iowa, and Nevada are known to contain units 

 that yield 10-25 gallons of oil per ton (Duncan and 

 Swanson, 1965, p. 15). Permian deposits of black 

 shale at some places contain 10-20 percent organic 

 matter, but most samples yield little oil. In south- 

 western Montana, a Permian black shale may yield 

 10-15 gallons of oil per ton in a 600-square-mile area. 

 In California, Miocene marine shales underlie an 

 area of 3,000 square miles and samples show a range 

 in yield from 3-30 gallons of oil per ton. 



Carbonaceous shales associated with coal beds con- 

 stitute a potentially large resource of shale oil be- 

 cause they occur throughout much of the United 

 States. Duncan and Swanson (1965, table 2) esti- 

 mated that these shales may yield 310 billion barrels 

 of oil, of which 60 billion barrels would be from 

 higher grade oil shale (25-100 gallons of oil per ton) . 



Lacustrine deposits seem to be the best prospect 

 for finding new shale-oil resources in high-yield oil 

 shale because the best deposits currently known are 

 in the lacustrine Green River Formation of Eocene 

 age. It is unlikely that any other deposit of the 

 magnitude of the Green River Formation exists in 

 the United States, because it required a unique set 

 of conditions persisting for millions of years in ex- 

 tremely large shallow lakes. However, small high- 

 grade deposits may be present in the numerous unex- 

 plored lacustrine deposits of Tertiary age in the 

 Western United States (Feth, 1963), particularly in 

 Montana, Nevada, and Wyoming (Duncan and Swan- 

 son, 1965, p. 16). 



PROSPECTING TECHNIQUES 



Oil shales can usually be recognized on the out- 

 crop by their texture, color, and low specific gravity, 

 but the evaluation of an oil-shale deposit requires 

 core drilling to obtain unweathered samples that are 



representative of the buried deposit. Other tech- 

 niques are available for use in a preliminary evalua- 

 tion of a possible oil-shale deposit. If wells have been 

 drilled through the deposit for other purposes, such 

 as petroleum exploration, the cuttings of these wells 

 can indicate the presence or absence of good oil 

 shale. Geophysical logs of wells, such as sonic or 

 density logs, can be used in some places in predicting 

 the probable oil yield of the shales in the sedimen- 

 tary sequence (Bardsley and Algermissen, 1963). 

 For many years the U.S. Bureau of Mines has at- 

 tempted to evaluate the oil-shale resources of the 

 Green River Formation in Colorado, Utah, and Wyo- 

 ming by collecting and assaying cuttings of wells. 

 They were generally successful in indicating the 

 boundaries of the oil-shale deposit and the approxi- 

 mate magnitude of the resources, but they found 

 that individual sample sets could not be relied upon 

 because of the possibility of contamination, or acci- 

 dental enrichment, of the cuttings. 



In lacustrine deposits the richest oil shale is de- 

 posited in the center of the lakes, so a geologic 

 evaluation of the outcropping rocks in a basin may 

 point the way to the location of the depositional 

 center of the deposit, and thus narrow the area of 

 intensive search. 



PROBLEMS FOR RESEARCH 



Oil shale in the green River Formation contains a 

 wide variety of unusual minerals but the amount 

 and number are imperfectly known. Much explora- 

 tion and research is needed to identify the minerals, 

 to calculate the amount and extent of potentially 

 valuable minerals, and to investigate the feasibility 

 of recovering them as coproducts or byproducts in 

 a commercial oil-shale mining and retorting opera- 

 tion. 



Research is also needed in solving the techno- 

 logical problems of extracting the oil at low cost 

 and at minimum damage to the environment. En- 

 vironmental problems associated with the extraction 

 of shale oil by conventional retorting are magnified 

 because of the large volume of rock that would be 

 processed in a commercial operation. A plant pro- 

 ducing 100,000 barrels of oil per day would probably 

 mine about 130,000 tons of shale per day, and would 

 require the disposal of a similar amount of spent 

 shale. One problem would be to prevent the con- 

 tamination of streams either by saline water en- 

 countered in mining, or by leaching of salts from 

 spent shale. Other problems include the disposing 

 of the spent shale and the revegetating of the spent 

 shale if it is disposed of on the surface. 



