Geotechnical information is essential to the planning of any surface mining operation. This information includes data on rock strength and characterization of the discontinuities such as faults, fractures, or bedding planes within the oil sand and surrounding rocks.
In open pit planning, geotechnical information is necessary to select the proper mining equipment and design the pit slopes. For instance, if a rock is very hard, it would not be suited for bucket-wheel excavators or draglines without first blasting the material. A geotechnical study for an oil sand project is usually undertaken by a geotechnical group with specific expertise in this area. The first information that must be gathered is the geology of the deposit and its surrounding rocks. Separate units within the oil sand and overlying rocks should be identified for strength testing. Once the separate, identifiable units are recognized, samples for strength tests can be taken during the exploration drilling. These samples should be of unsplit core and be two to three times the core diameter in length. The tests to be performed on these samples should include a uniaxial compressive strength and triaxial shear test to determine the intact rock strength. The strength tests should be performed in at least two directions, parallel and perpendicular to the bedding.
Other important data characterizing the setting of an oil sand deposit include rock mass discontinuities such as the joints, faults, and bedding planes within a deposit. The techniques for obtaining data on these features include geologic mapping and fracture mapping where surface exposures are available and collection of Rock Quality Determination (RQD) data from drill core.
SUMMARY
Tar sands deposits constitute a hydrocarbon resource that far exceeds the world’s resources of conventional oil. The most economical means of exploiting the near surface part of this resource is through surface mining. The exploration techniques described in this section should provide the information on the grade and geometry of the deposit as well as the hydrological and geotechnical conditions that are necessary to plan a successful tar sands surface mine.
2.9 Oil Shale Exploration and Geology R.W. Elayer, I.P. Dorling, and P.W. McKie
INTRODUCTION
Oil shale, long known as a potential source of energy, is found in many countries. The largest known deposits occur in the United States, primarily in Colorado, Utah, and Wyoming.
Even though numerous occurrences of oil shale are known, interest in their development has been, until recently, insufficient to support the thorough exploration and appraisal of known deposits or to encourage the search for additional deposits. However, during the past few years, a great deal of oil shale exploration and assessment work has been performed in the western United States, Australia, Morocco, and Brazil, with a view to commercial development.
In the past, oil shale has been commercially mined and used directly as a fuel, or processed into liquid fuels, in many parts of the world including Scotland, France, Sweden, South Africa, Australia, the Soviet Union, China, Brazil, and the United States. At the present time (1985), oil shale is being commercially mined and processed in only two countries. In the Soviet Union, (Estonia), oil shale is used directly as a fuel to generate electricity, and in the People’s Republic of China (Fushun and Maoning), oil shale is used to produce liquid fuel and gas. Large open pit oil shale projects have been planned in Brazil, Morocco, and Australia while development of a commercial sized underground oil shale mining and processing operation is already underway in Colorado.
Definition of Oil Shale
Oil shale, in a strict sense, is a misnomer, since it does not contain oil and it is not
necessarily a shale, as defined geologically. According to ASTM (1985), oil shale can be defined as a sedimentary rock containing insoluble organic matter that upon heating yields an oil similar to petroleum. Shale oil is the organic liquid obtained from the retorting of oil shale.
Oil shales are diverse in composition, lithologic association and genesis, and range in color from light shades of brown, green or red to dark brown, gray or black. Claystone, marlstone, siltstone, impure limestone, and black shale most often contain enough insoluble organic material to be classified as oil shale. Three general categories of oil shale are known: carbonate-rich shale, siliceous shale; and cannel or coaly shale.
Individual deposits of oil shale yield shale oil in greatly varying amounts. Some yield more than 38 L (10 gal) of shale oil per ton and others yield more than 380 L (100 gal) of shale oil per ton.
World Occurrence of Oil Shale
The world occurrences, geology, and resources of oil shale are well documented by Duncan and Swanson (1965). Oil shale deposits are found in every continent of the world, however, information on their quality, thickness, and extent is varied. The principal known deposits throughout the world are shown in Fig. 2.9.1.
Figure 2.9.1.
The most important and largest known oil shale deposits of the world are found in the western United States. These deposits are located in Colorado, Utah, and Wyoming, and comprise some of the highest grade resources known. Other important deposits in the United States are found in Indiana, Kentucky, Illinois, Iowa, Michigan, Montana, Nevada, New York, Ohio, Oklahoma, Tennessee, Texas, and Alaska.
Many organic-rich shale deposits are known to exist in Canada, although little data are available concerning them. One of the most important Canadian resources is found in New Brunswick. Other deposits occur in Newfoundland, Nova Scotia, the Northwest Territories, Ontario, Quebec, and the Yukon.
Potentially large deposits of oil shale are known to exist in South America, particularly in Brazil. Smaller deposits are also known to occur in Argentina, Chile and Uruguay. Several large deposits of oil shale occur in Africa, notably in South Africa, Morocco, and Zaire. The Moroccans have been actively working on development of their Timahdit and Tarfaya deposits.
In Asia, the largest and most extensive known oil shale deposits are found in the People’s Republic of China and the Soviet Union. About 180 “commercial” oil shale deposits occur in China, distributed in 21 provinces (Duncan and Swanson, 1965). The most important resources are located in Manchuria, Heilingkiang, Kwantung, and Sinkiang provinces. Many deposits of oil shale are reported in Siberia, particularly in Kazakhstan, Kuznetsk, and in northeast Siberia.
Elsewhere throughout Asia, rich but small deposits of oil shale are located in western Thailand, eastern Burma, and northwest Turkey. Extensive deposits also exist in Israel, Jordan, and Syria. Many small, high-grade oil shale deposits are found in Australia and New Zealand. In particular, oil shale is widely distributed in New South Wales, Queensland, and Tasmania.
The oil shale deposits of Europe are extensive and widely distributed. Some of the most important occur in Scotland and Estonia, France, Spain, Sweden, Austria, Bulgaria, Czechoslovakia, Italy, Germany, Switzerland, Yugoslavia, and Portugal. Detailed data
are available concerning many European oil shale occurrences, particularly about those in Scotland, France, Estonia, Spain, and Sweden, which have been commercially developed during the past 130 years.
Oil Shale Geology
The world’s known oil shale deposits range in age from Cambrian to Recent. The oldest deposits include those found in northern Europe, northern Asia, and east-central North America, while some of the youngest are found in the Green River formation of the western United States, and in China.
Three major depositional environments in which oil shale was formed have been identified. These are large lakes (lacustrine environment); shallow seas (continental platform or shelf environment), and small lakes, streams, and lagoons (coal-forming swamp environment). In these environments, oil shale was deposited from water containing a prolific quantity of flora and fauna, in conditions that precluded oxidation of the organic material which accumulated on the bottom of the depositional structures. Oil shales formed in a large lacustrine environment include, most importantly, those of the Green River formation (Eocene in age) found in Colorado, Utah, and Wyoming; the Paraiba River Valley deposit (Pliocene) of southern Brazil; the Albert Shale (Mississippian) of New Brunswick, Canada; and the Aleksinac deposit in Yugoslavia. Such deposits form some of the highest grade, thickest, and most extensive oil shale resources in the world. They are predominantly calcareous and often interspersed with volcanic tuffs, clastic sediments, and carbonate rocks.
Those oil shale deposits which were formed in a shallow sea or continental platform/shelf environment, include the marine black shales of northern Siberia and northern Europe (Cambrian); the high-grade kukersite deposits (Ordovician) of Estonia; the Devonian black shales of the eastern and central United States; the Permian shales of Brazil, Uruguay and Argentina; and the Jurassic black shales of Europe and eastern Asia. These deposits are predominantly siliceous in character and extend over large areas. They are associated with limestone, chert, sandstone, and phosphatic nodules. Oil shales which were formed in small lakes and found associated with coal-bearing rocks include the thick, extensive, and high-grade deposits of Fushun (Tertiary) in Manchuria, China and those of late Carboniferous age in Kazakhstan in the Soviet Union. These deposits overlie, or are associated with, coal seams.
Oil Shale Resources
Duncan and Swanson (1965) compiled an order-of-magnitude estimate of the world’s oil shale resources (see Table 2.9.1). Since this estimate was compiled, considerable work has been performed on oil shale deposits in many areas of the world. Known oil shale resources in Australia and Brazil, for example, have been considerably increased due to recent exploration.