Unconventional liquid fuels are more polluting than conventional oil. Wholesale development of tar sands, shale oil, kerogen, and other unconventional oil resources will likely doom humanity’s attempt to rein in greenhouse gas emissions and almost certainly tip the world toward climate chaos.
The liquid fuels that can be produced from tar sands, oil shale (or kerogen), shale oil formations, and coal are generally lumped under the term “unconventional oil.” Coal-to-liquids technology has been known for decades—Nazi Germany used it during World War II—but has never been economically competitive with conventional crude oil and is not projected to grow into a major energy source. Tar sands and shale oil, however, have received significant attention and investment in recent years, with promoters claiming that these sources could soon make North America oil-independent.
Tar sands production is already commercially viable (with oil prices over about $60 per barrel) and has increased rapidly over the past decade. Tar sands contain a viscous substance called “bitumen” (similar to very heavy crude oil) tied up in sand or clay. The greatest known reserves are in Alberta, Canada. Typically, tar sands are strip-mined and the bitumen cooked out. Natural gas has been the primary energy source to do this, making the greenhouse gas footprint of tar sands oil far larger than that of conventional oil. The process also causes deforestation and leaves toxic lakes of wastewater slurry. Some of the environmental impacts associated with tar sands may decrease in the future as the industry adopts in situ extraction methods that are claimed to make the environmental impacts comparable to conventional oil operations.
Oil shales are widely distributed around the world but the largest deposits are in the western United States. Roughly two-thirds of known oil shales, containing an estimated 1.7 trillion barrels of oil equivalent, are found in Wyoming, Utah, and Colorado. In oil shales, the hydrocarbons are in the form of kerogen, a precursor to oil that has not been heated long enough by geological processes to become oil or natural gas. Oil shales can be converted to oil and natural gas through a variety of techniques, most of which require heating the rock above 600ºF (315ºC).
Shale oil, also known as “tight oil,” is high-quality light crude that is trapped in rock formations of low permeability. The horizontal drilling and hydraulic fracturing (“fracking”) techniques used for shale gas production have recently been successfully applied to shale oil production, primarily in North Dakota and Texas. Costs are high and from early data it appears that, like shale gas wells, shale oil wells may have fairly low lifetime productivity.
Some estimates put the total resource in tar sands, oil shales, and shale oil at 6 trillion barrels, more than known conventional oil reserves. But extracting oil from these sources has proven to be much more energy-intensive and damaging than conventional oil production, and poses a grave threat to both local ecosystems and the global climate. The enormous technical complications of unconventional oil suggest that it will be extremely challenging to ramp up their production to fully replace declining conventional oil resources at the scale and rate needed.