by: Paul Kando
The 72 tank-car train that derailed in the middle of picturesque Lac Megantic, Quebec, killing 47 and destroying the town center, carried shale oil from North Dakota to New Brunswick. There is an oil boom in North Dakota, one of our "new sources of domestic crude".
Of course shale oil is not new. It was first extracted by the Syrian physician Masawaih al-Mardini in the 10th century. The first extraction patent was granted by the British Crown in 1684. Modern industrial extraction started in France in 1838 and by late 19th century, shale oil recovery plants operated in the U.S., Australia, Canada, and Brazil. The 1920s discovery of pumpable crude in Texas and the Middle East brought to a halt most shale oil production but, as part of the Synthetic Liquid Fuels Program, the US restarted it in 1944. Limited production ended again when oil prices fell in the 1980s, with the last U.S. oil-shale retort closing in 1991. U.S. production restarted again in 2003, and the Energy Policy Act of 2005 authorized the extraction of oil shale and tar sands on federal lands.
The reason for this bumpy ride is the high cost of recovery, in terms of both money and energy. Oil shale must be decomposed before the kerogen it contains can be converted into a petroleum-like synthetic crude. The process usually consists of pyrolysis, hydrogenation, and sometimes cracking.
Pyrolysis thermochemically decomposes organic matter at elevated temperatures, in the absence of oxygen or any halogen (a group of five chemically related elements: fluorine, chlorine, bromine, iodine, and astatine). It results in an irreversible, simultaneous change of chemical composition and physical phase.
Hydrogenation is a chemical reaction that adds hydrogen to an organic compound . The hydrogenated compound is said to become more 'saturated' - a term familiar from health concerns associated with hydrogenating unsaturated dietary fats to produce saturated fats and trans-fats.
Cracking breaks down complex organic molecules like kerogen and heavy hydrocarbons into simpler molecules like light hydrocarbons, by breaking the carbon-to-carbon bonds. In short, hydrocarbon cracking breaks long-chain hydrocarbons into short ones.
Oil shale can be processed in a number of ways, both conventionally (ex situ) and in situ. In the former, kerogen-bearing rock is mined, crushed and then retorted (the processing vessel is called a retort). Processed in situ, the rock is fractured ("fracked") and retorted in place. The oil is recovered by pumping. Different methods produce shale oil with different properties.
In the oldest, most common extraction method, oil shale is heated until the kerogen decomposes into shale oil vapors and combustible oil shale gas. The vapors and gas are cooled and the shale oil condenses. What's left is spent oil shale consisting of minerals and char, a carbon-rich residue. Burning the char produces oil shale ash, which can be used in cement or brick manufacture. Depending on the oil shale, there may be other valuable byproducts, such as waxes, ammonia, sulfur , aromatic compounds, pitch and asphalt.
Pyrolyzing the shale requires energy, usually coming from another fossil fuel, like natural gas, oil, or coal. Electricity, radio waves, microwaves, and reactive fluids have been also used experimentally. The heat contained in hot spent shale and ash may be used to pre-heat raw oil shale. Gas and char byproducts may be burned for energy as well. In above ground processing, the mined shale must be crushed into smaller pieces, to increase the surface area for better extraction.
The temperature at which decomposition occurs depends on the time-scale of the process. In above ground processes it begins at 570°F, but proceeds faster and more completely at higher temperatures. The greatest oil yield occurs between 900 and 970°F. Above 1,110°F the limestone and dolomite in the mined rock decompose as well, causing large carbon dioxide emissions, not to mention the additional energy use. Therefore lower process temperatures are preferred. A modern below ground (in situ) process may take several months of heating, with decomposition achieved at temperatures as low as 480°F. Hydrogenation and thermal dissolution extract oil using hydrogen-donor compounds and/or solvents applied at elevated temperatures and pressures, increasing oil output by cracking the dissolved organic matter.
Shale oil yield is not very impressive: About 1/6th of the Green River Formation (Utah, Wyoming, Colorado), which is said to hold "more oil than the rest of the world put together", yields 25 to 100 gallons of oil per ton of rock processed. Another 1/3 yields only 10 to 25 gallons per ton, the rest less. Not surprisingly energy invested in shale oil for energy returned (EROEI) is nothing to crow about. Depending on how energy from the extraction process itself is utilized, it ranges from 1:2.1 to 1:16, with an average of around 1:4. Waste disposal is a problem, as are excessive water use, waste water management, water and air pollution -- none of which factor in the above EROEI numbers (nor are spills, train explosions and other sundry events). Compare with solar PV at 1:6.9, wind 1:18, and wave power at 1:15 - without the problems.
There exists no economically viable way yet known to extract and process oil
shale for commercial purposes observed a 2011 report by the U.S. Bureau of Land
Management (Federal register 21003-21005). Food for thought.