Geoscience Reference
In-Depth Information
Tailing pond
Mine
Tailing pond
Athabasca River
Tailing pond
(a)
(b)
Figure 20.28 Millennium pit mine in Alberta, Canada. (a) The Millennium mine is a gargantuan open-pit mine that is used to access
oil sands. This mine produced over 300,000 barrels of oil per day in 2012. (b) ASTER image of the Millennium mine from NASA's Terra
satellite in 2007. Note the large size of the mine, the tailing pond where waste is stored, and its close proximity to the Athabasca River.
The United States currently imports about 2 million barrels a
day from this source. The semi-solid oil in Canada is extracted
either by open-pit mining at the Earth's surface (Figure 20.28)
or by injecting steam into the oil-bearing sands at depth. This
infusion of hot water through the wellbore liquefies the semi-
solid bitumen so that it can be brought to the surface in the
well. Several other methods have also been used to extract oil
from these deposits, including injection of a hydrocarbon sol-
vent to separate the oil from the sand.
In the United States unconventional oil resources are typi-
cally associated with shale rock units generally referred to as
oil shales . Recall from Chapter 12 that shale consists domi-
nantly of lithified clays that accumulated in calm coastal bays
and lagoons (Figure 12.12). According to the United States
Geological Survey, the contiguous United States contains
abundant shale deposits that hold vast quantities of oil and
natural gas. Each of these areas is called a shale play that is
controlled by a unique set of geological circumstances within
the area and is a favorable site for exploration. Such plays are
named after the host shale in which the fossil-fuel reserves
are contained, including the Marcellus in the northeast, the
Antrim in Michigan, the Bakken in the northern Great Plains,
the Mancos in the Rocky Mountains, and the Monterey/Santos
in California, to name a few (Figure 20.27). Although these
shale plays are known more for the amount of natural gas they
contain (the Marcellus Shale holds approximately 410 trillion
cubic feet of natural gas, for example), many hold significant
oil reserves. For example, the Bakken Shale is believed to
contain about 4 billion barrels of oil, but may contain more.
On the Pacific coast, the Monterey/Santos play is estimated to
hold about 15 billion barrels of oil.
Oil from shale plays is extracted with a method called
hydraulic fracturing (or fracking ). In a fracking operation, wa-
ter, sand, and various chemicals are injected down the well bore
into the oil-bearing strata. When it reaches that level, it creates
fractures in the rock that permit the oil (as well as natural gas)
to escape and flow out of the well (Figure 20.29a). In contrast
to conventional wells, fracking permits horizontal drilling into
rocks, which extends the reach of the mining operation. Frack-
ing is widely popular at the present time, with over 40,000 wells
installed nationwide between 2011 and 2013. The Bakken play
in North Dakota has experienced such explosive growth that
the artificial lights associated with operations there can now be
seen from space (Figure 20.29b). As a result, production of U.S.
oil rose from about 100,000 barrels of oil per day in 2003 to
2 million barrels per day in 2012.
Is the Environment Threatened
by Fracking?
Given our nation's current dependence on oil to fuel large parts
of our economy, many people are understandably excited about
the potential these unconventional sources have in enhancing
our supply needs. The development of these resources also
shows much promise for reducing our dependence on oil from
unstable countries and enhancing our overall energy security.
Shale play A geographic area, dominated by shale bedrock,
that is targeted for exploration due to favorable geological con-
ditions that suggest high potential to yield an economic quan-
tity of oil or natural gas.
Hydraulic fracturing Fracturing of rock at depth by the injec-
tion of fluids to release oil and natural gas contained within
shale beds.
 
 
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