Geology Reference
In-Depth Information
Unconventional oil
is oil acquired by means other than drilling a traditional
borehole in the ground. It includes oil shale, oil sands (tar sands), heavy oil, oil
synthetically produced from coal or natural gas, natural gas liquids, and lease con-
densate (a liquid byproduct of natural gas extraction at the well, or “lease,” site).
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Thanks to horizontal drilling and hydrofracking, shale oil production has grown
to provide 29 percent of total crude oil production the United States, and 40 percent
of total US natural gas production, according to the US government's Energy In-
formation Administration (EIA).
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In a 2013 study of 41 countries, the EIA raised its estimates of global shale oil
and shale gas reserves. According to the new report, 10 percent (or some 345 billi-
on barrels) of the world's recoverable crude oil resources, and 32 percent (or 7,299
trillion cubic feet) of global natural gas resources, are found in shale formations.
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(These estimates remain uncertain until more data become available.) More than
half of the shale oil resources outside the United States are concentrated in four
countries: Russia, China, Argentina, and Libya. More than half of the shale gas out-
side of the United States is found in China, Argentina, Algeria, Canada, and Mex-
ico. For now, the United States and Canada are the only nations producing shale oil
and gas in commercial quantities.
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Unconventional fuels tend to be more difficult to reach, more expensive to pro-
duce, and more polluting than conventional fossil fuels. These factors have made
them a target of environmentalists. But as conventional supplies become depleted,
unconventional fuels will prove increasingly important.
Shale gas is natural gas that is trapped in minute deposits embedded in shale rock
formations (much the way small air pockets form in a loaf of bread as it bakes).
Shales are fine-grained sedimentary rocks. There are different kinds of shale, but
the most common is “black shale,” which formed in deep water and without any
form of oxygen present. Shale gas is usually accessed through a combination of
vertical and horizontal drilling, and hydrofracking.
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About 33,000 natural gas wells are drilled in the United States annually, and
today nine out of ten of them use fracking.
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The recent boom in shale gas has been phenomenal. As recently as 2000, shale
gas provided only 1 percent of the natural gas produced in America. By 2010 it was
