Close your eyes and imagine a tar pit. What comes to mind? For many of us it's a black, molasseslike lake with preserved saber-toothed tigers.
Tar pits are better known as oil sands, tar sands and bituminous sands, and they aren't only of interest to scientists -- they're also of great interest to energy companies. But just like the name suggests, this black gold doesn't gush from a geyser; it's actually in the sand itself.
Oil sands are a mixture of roughly 90 percent clay, sand and water, with 10 percent bitumen [source: Grist]. The dark, sticky sands look similar to topsoil, are viscous when warm and freeze as solid as concrete in cold temperatures. But calling them "tar" pits or "tar" sands is misleading -- the thick black substance isn't tar, but rather bitumen. Bitumen is composed of a mixture of hydrocarbons. It's petroleum that exists naturally in a solid or semisolid state, but unlike conventional petroleum, which is in natural liquid form, bitumen needs to be separated from the sand before it can be used.
More than 2 trillion barrels of the world's petroleum lies in oil sands, though most will never be dug and processed because it's too deep [source: Grist]. Oil sands are found worldwide, from Canada to Venezuela and, as you might imagine, in the Middle East. Alberta, Canada, has a booming oil-sand industry -- as many 1 million barrels of synthetic oil are produced there every day, 40 percent of which comes from oil sands [source: Oil Shale & Tar Sands Programmatic EIS Information Center].
It's estimated that Alberta may have as much as 300 billion barrels of recoverable oil, as well as exponentially more that can't be tapped until the development of new technologies for retrieval. That volume means that Canada is one of the largest oil producers in the world, second to Saudi Arabia [source: Wired].
How do you go about straining oil from sand? Next we'll look at how bitumen is extracted, processed and transformed into some surprising products you use every day.
Squeezing Oil From Sand
Most bitumen is refined for use in gasoline, jet fuel and home heating oil, but petroleum also makes its way into more than 3,000 products you might not expect: ballpoint pens, lipstick, flying discs, even T-shirts. Before it can be used for anything, though, it first needs to be extracted from the sand and then processed.
There are a few different ways to mine bitumen.
Shallow reserves, which make up about 20 percent of oil sands, are recovered through surface mining, which is mining through open pits [source: Grist]. The process of surface mining differs a bit from company to company but generally includes conditioning, separation and froth treatment.
Conditioning starts the process of separating sand and bitumen and breaks apart any large pieces of oil sands. The oil sand is mixed with warm water -- called a slurry -- and transported by pipeline to an extraction facility. Here, the slurry is put through a separation process where sand sinks to the bottom and impure bitumen froth rises to the top. The froth is steamed, deaerated and diluted with naphtha to remove any lingering solids and promote flow. Diluted bitumen is processed in inclined plate settlers (IPS) and centrifuges -- both methods further clean the bitumen. And after all that, extraction is finished.
Deeply deposited bitumen reserves aren't reachable through open-pit digging and are recovered using in situ techniques, the most successful known as SAG-D. SAG-D is steam-assisted gravity drainage, a method that involves injecting steam into wells within the oil sand. The intense temperature and pressure separate the bitumen and water from the sand, and the bitumen -- rendered soft with the heat -- surfaces while the sand stays put. Other in situ techniques include toe to heel air injection (THAI), a relatively new process that combines both vertical and horizontal air injections into underground wells, and a vapor extraction process (VAPEX), similar to SAG-D but with a solvent injections instead of steam.
Refined bitumen is then ready to be transported and upgraded into synthetic crude oil and other petroleum products.
Recovering bitumen and transforming it into synthetic crude oil is dirty work, literally and environmentally. The mining and processing needed to produce a single barrel of upgraded synthetic crude oil uses between 2 to 4 barrels of water, an amount of natural gas equal to what's needed to heat a home for four days [source: Worldwatch Institute]. Rendering a single barrel also destroys 4 tons of earth [source: Worldwatch Institute]. Additionally, oil-sand extraction and processing operations are responsible for 4 percent of Canada's greenhouse gas emissions, emissions that are expected to triple by 2020 [source: The Press-Enterprise]. Mining also puts rivers and forests (including Canada's boreal forest, one of the world's largest intact ecosystems) at risk. As if that's not enough to worry about, two Canadian toxic dumps for tailings, the heavy metal-rich waste created during the separation process, can be seen from space [source: Worldwatch Institute].
Canada, for instance, is trying to deal with these environmental ramifications of rendering oil sands by requiring oil companies to refill old pit mines and plant trees. Efforts to lower fossil-fuel dependency, however, would lessen the need for energy-intensive, low-yield mining and minimize the blights that result from extraction.
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More Great Links
- "About Tar Sands." Oil Shale & Tar Sands Programmatic EIS Information Center. U.S. Department of the Interior, Bureau of Land Management. http://ostseis.anl.gov/guide/tarsands/index.cfm
- Clark, K.A. "Separation of Bitumen from Bituminous Sands." Nature. http://www.nature.com/nature/journal/v127/n3197/abs/127199a0.html
- Gillies, Rob. "Oil sands create environmental concerns." The Press-Enterprise. 2008. http://www.pe.com/business/local/stories/PE_Biz_S_canadaoil24.2d60439.html
- Goffman, Ethan. "Environmental Refugees: How Many, How Bad?" Discovery Guides. CSA. 2006. http://www.csa.com/discoveryguides/refugee/review.php
- Herro, Alana. "Oil Sands: The Costs of Alberta's 'Black Gold'." Worldwatch Institute. 2006. http://www.worldwatch.org/node/4222
- Koerner, Brendan I. "The Trillion-Barrel Tar Pit." Wired. 2004. http://www.wired.com/wired/archive/12.07/oil.html
- Mullins, Justin. "Invention: Oil-sands digester." New Scientist. 2008. http://technology.newscientist.com/article/dn14750-invention-oilsands-digester.html
- Oil Sands Discovery Center. http://www.oilsandsdiscovery.com/
- "The Oil Sands of Alberta." 60 Minutes. CBS News. 2006. http://www.cbsnews.com/stories/2006/01/20/60minutes/main1225184.shtml
- Romm, Joseph. "'Time' for tar sands." Grist. 2008. http://gristmill.grist.org/story/2008/5/27/135238/695