The term refers to a form of sandstone which contains sand, clay and water and is saturated with a dense viscous form of petroleum that is similar to bitumen or tar. Extraction of the heavy oil from the sandstone formation requires substantial amounts of energy. More conventional forms of oil are extracted simply by sinking a well into a reservoir of oil below the ground. This oil naturally flows into the pipe and is pumped to the surface. The bitumen is heavier and requires either strip mining (not usually available because of the depth of the tar deposits) or injecting steam, hot water or solvents into the well to make the petroleum flow. This later, more common method requires a lot of water and energy (for heating and pumping) to extract the oil.
The use of substantial volumes of water and solvents in tar sand extraction makes it similar to fracking for shale gas. Both are considered by many as producing more adverse environmental impacts, so-called hard-to-get fossil fuel, than other forms of fossil fuel. Also because the tar sand oil is so thick, it has to be diluted, often with lighter fractions of oil, in order to transport it through pipelines.
Some further ideas to explore on Global Warming Potential:
Compare gas from fracking, oil from tar sands, and conventional oil from on-shore oil wells and determine which form of energy produces the most Greenhouse Gases through its entire life cycle – from extracting the fossil fuel to refining it to using it?
Why is the European Union evaluating the levels of GHG emissions associated with the extraction and use of oil from tar sands?
“About Tar Sands,” U.S. Department of the Interior, Bureau of Land Management (BLM)
Robert Kunzig, “The Canadian Oil Boom,” National Geographic, March 2009
Tar Sands Action