Sunday, December 28, 2008
Opinions differ about what role oil will play in the energy future of the United States and what role oil shale should have. Should oil shale be developed and, if so, when and how? Many geologists, engineers, physicists, chemists and others have been studying oil shale and its potential for years and have established some basic facts.
The oil shale (technically marlstone) was deposited in a large lake or lakes that existed in western Colorado, eastern Utah and southwestern Wyoming during the Miocene epoch about 15 million years ago.
Clay, sand and silt were washed into the lake from surrounding highlands, and prolific organic material lived and died in the lake.
These deposits, called the Green River Formation, were covered by younger deposits and later exposed by erosion.
Importantly, the oil shale was not covered by a great enough thickness of sediment to create the heat and pressure necessary to generate conventional crude oil. The hydrocarbon produced is called kerogen.
The heat to liquefy the kerogen and release it from the rock must be supplied by some process devised by humans.
The processes that have been attempted on an experimental basis can be lumped together as (1) mining the shale, crushing it and heating it in a retort and (2) heating the shale underground, in situ, and pumping the released oil to the surface.
Engineers and geologists have invested a great deal of time in developing these methods, and chemists have studied the properties of the oil and the most efficient ways to get it out of the rock.
Mining the shale would leave a lot of spent rock to be disposed of (an average ton of rock contains about 30 gallons of oil, and there are 42 gallons to a barrel of oil).
Shell Oil has been a leader in developing new technologies in oil shale extraction in recent years.
Much of the information discussed here is from an October 2007 article in Fortune magazine detailing Shells method called the In Situ Conversion Process or ICP.
The in situ method being used in Shell Oils experimental tract involves drilling a well through the oil shale layer (about 2,000 feet) and lowering heated rods that will eventually heat the shale to 650 degrees Farenheit to release the oil.
It may take about a year for the shale to reach the necessary temperature. Once the oil is freed from the rock, it is pumped to the surface much like in a conventional oil well.
Shell recovered 1,700 barrels of light, high-quality oil from a 30-foot by 40-foot test area using this method. In a commercial-sized tract, an ice barrier would have to be formed around the tract to prevent contamination of the surrounding ground water.
According to a Rand Corp. estimate, a power plant would have to be constructed that would consume 5 million tons of coal per year to produce 100,000 barrels of oil per day.
However, Shell says it could obtain the needed energy from the natural gas produced by the process.
The shale for a retort could be obtained from an open pit mine that would be 2,000 feet deep. It is estimated that three barrels of water would be needed to process one barrel of oil and that about a million barrels of oil could be produced from an acre.
Several companies were players in the development of shale oil during the 1960s and 1970s, including Tosco, Union Oil, Paraho, Occidental and others.
Some of these companies produced some oil from their projects, proving it can be done.
Union Oil, for example, produced a total of 13,000 barrels of shale oil from processing 1,200 tons of rock per day at its facility on Parachute Creek.
A pipeline would then be needed to get the resource to market. Because the oil is a heavier grade and has some different chemical properties than most conventional crude oil, it would have to be heated to keep it liquid.
So it seems that getting enough shale oil on the market to be a significant part of the energy supply will not be a simple matter.
Jack Roadifer holds a doctorate in geology from the University of Arizona. He also worked as an oil company geologist for seven years and taught geology at Mesa State College for 31 years. He is now retired and a volunteer at the Math & Science Center and at the Mesa County Public Library.
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