The recent increases in petroleum prices have spurred renewed interest in the development of oil shale resources worldwide, including the vast deposits of the Green River Formation in Colorado, Utah and Wyoming.
Oil shale has been a difficult commodity to exploit economically. Since the early 1900s, many attempts have been made to wrest shale oil from the Green River deposits, but with little success. The higher costs of mining oil shale, the lack of a viable technology to economically recover oil from the shale and the cost of environmentally acceptable disposal of waste rock have been limiting factors in developing an oil shale industry.
Shell Oil Co., for one, hopes to resolve these constraints with its in situ retorting technology being field tested in the Piceance Creek Basin in northwestern Colorado. This process involves placing an electrical heating element in a heater hole, which is surrounded by a number of closely spaced production wells (left).
The shale must then be heated for several years to reach a temperature at which the organic matter decomposes into hydrocarbons for recovery by the production wells.
One major advantage of this method is that the inert mineral fraction, which amounts to 75-85 percent by weight of the raw oil shale, remains in place. The in situ process may not require mine workings or large surface plant facilities to crush and retort the shale, and it avoids the necessity of removing overburden and waste shale to dumps with its consequent environmental problems.
However, factors that need to be determined prior to in situ commercial production are:
- The cost of the energy required to heat the oil shale.
- The amount of surface area that will be disturbed.
- The disposal of produced water.
- The potential for groundwater pollution.
In addition, protection or recovery of potentially valuable sodium carbonate minerals commingled with oil shale -- including nahcolite (NaHCO3) and dawsonite [NaAlCO3(OH)2] -- in the deeper part of the Piceance Creek Basin must be considered.
The U.S. government has tasked the Bureau of Land Management (BLM) with augmenting a research and development program for the Green River oil shale deposits on federal lands in Colorado, Utah and Wyoming.
Twenty nominations for 160-acre RD&D (Research, Development and Demonstration) tracts on federal oil shale lands were initially received by the BLM in 2005. Ten were in Colorado, nine in Utah and one in Wyoming. Major energy companies submitted most of the nominations, and a majority of the Colorado nominations were for testing in situ technologies.
A team consisting of personnel from the Department of Energy, appropriate agencies of the three states and the BLM ranked the 20 nominations by their merits. The results were forwarded for final approval by the Department of the Interior (DOI). The DOI will announce the results this spring after completing a comprehensive Environmental Impact Statement.
Panoramic view of a room-and-pillar oil shale mine in northeastern Estonia. The thickness of the mined oil shale (kukersite) is about 2.5 meters. Oil shale is also mined by open pit at several nearby localities.
Photo taken in 2005 courtesy of Heikki Bauert, Tallinn, Estonia
Relatively small oil shale industries are operating in Europe, South America and Asia.
The largest is in Estonia, where high-grade marine oil shale (kukersite) of Ordovician age has been mined for many years. About 12 million metric tons of oil shale is mined yearly in several underground and open pit mines. About 85 percent is burned as fuel in several large electric power plants in northeastern Estonia and the remainder is retorted for shale oil, which is used in the manufacture of fuels and petrochemicals.
Although the Estonian oil shale industry has been a major source of airborne and water pollution in the past, burning the shale in new circulating bed combustors that are being installed in two electric power plants has significantly reduced air pollutants.
In Brazil, oil shale in the marine Permian Iratí Formation, mined by open pit near the town of Sáo Mateus do Sul in the state of Paraná, is retorted for shale oil, liquefied petroleum gas, sulfur and fuel gas.
Shale oil is produced from Tertiary shale of lacustrine origin at Fushun in the province of Liaoning, China. Until 2005, Australia was producing shale oil from the Stuart oil shale, a lacustrine deposit of Tertiary age, in eastern Queensland. The shale was retorted in an Alberta Tacuik Processor, a horizontal retort. Over a million barrels of low sulfur shale oil have been produced and marketed.
The operation is currently closed for economic evaluation.
Although these oil shale operations represent only a small fraction of the world fossil energy market, potential resources of oil shale are huge. In 2003, an inventory of the world’s resources by the U.S. Geological Survey (included 39 countries) was estimated to be about 3.3 trillion in-place barrels of shale oil, but the ultimate resource is undoubtedly much larger.
An estimated l.7 trillion barrels are in the Green River deposits in Colorado, Utah and Wyoming, of which one trillion barrels are in Colorado. How much of the Green River resource is recoverable using today’s mining and retorting technologies has yet to be determined, but likely it will exceed several hundred billion barrels.
Another potential resource of shale oil in the United States is the Devonian-Mississippian marine black shales of Kentucky, Indiana, Ohio, Alabama and Tennessee. The best of these shales contains an estimated 189 billion barrels in near-surface beds amenable to open-pit mining.
The world is thus well endowed with oil shale resources. The question is: Can shale oil be recovered economically to compete with petroleum?
Estimates of the lead-time to construct a 50,000 barrel-per-day oil shale plant are in the range of 10 to 20 years. If world petroleum production peaks within the coming decade, it would be advantageous for the government and industry to move soon on a plan of action. The Department of Energy and some major oil companies have taken steps in planning for an oil shale industry, and the BLM has started leasing research and development sites in the western states.
Historically, energy sources have moved from wood to coal to oil and gas. Possibly shale oil will become the bridge between the impending shortage of petroleum in coming years and a transition to hydrogen and renewable energy sources.
(Dyni and Johnson are both with the U.S. Geological Survey, Denver. All trade, product and firm names are used for descriptive purposes only and does not imply U.S. government endorsement.)