Chesapeake Energy natural-gas well site near Burlington, Pa.
plays a key role in our nation’s clean energy future. The U.S. has vast
reserves of natural gas that are commercially viable as a result of
advances in horizontal drilling and hydraulic fracturing technologies
enabling greater access to gas in shale formations. Responsible
development of America's shale gas resources offers important economic,
energy security, and environmental benefits.
Although we’ve known for many years that natural gas was trapped in hard
dense deposits of shale formed from ancient sea basins millions of years
ago, we did not have the technology to access these resources economically
until recently. As a result, previously uneconomic natural gas resources
are now available for exploration and development. In the last five years,
natural gas reserves grew 30 percent and in the last few years alone we
have increased onshore natural gas production by more than 20 percent –
an accomplishment that most energy experts thought impossible a few years
ago. Shale gas “plays” are found throughout the Mountain West, the
South and throughout the Northeast’s Appalachian Basin. These plays are
geographic areas where companies are actively looking for natural gas in
shale rock. The Barnett core in Texas, for example, is 5,000 square miles
and provides 6 percent of U.S. natural gas. The Marcellus fairway that
blankets Pennsylvania, New York, Ohio and West Virginia covers ten times
the square miles of the Barnett, but has only recently started to be
What is shale gas and why
is it important?
Shale gas refers to natural
gas that is trapped within shale formations. Shales are fine-grained
sedimentary rocks that can be rich sources of petroleum and natural gas.
Over the past decade, the combination of horizontal drilling and hydraulic
fracturing has allowed access to large volumes of shale gas that were
previously uneconomical to produce. The production of natural gas from
shale formations has rejuvenated the natural gas industry in the United
Does the U.S. Have
Abundant Shale Gas Resources?
Of the natural gas consumed
in the United States in 2009, 87% was produced domestically; thus, the
supply of natural gas is not as dependent on foreign producers as is the
supply of crude oil, and the delivery system is less subject to
interruption. The availability of large quantities of shale gas will
further allow the United States to consume a predominantly domestic supply
the EIA Annual Energy Outlook 2011, the United States possesses 2,543
trillion cubic feet (Tcf) of potential natural gas resources. Natural gas
from shale resources, considered uneconomical just a few years ago,
accounts for 862 Tcf of this resource estimate, more than double the
estimate published last year. At the 2010 rate of U.S. consumption (about
24.1 Tcf per year), 2,543 Tcf of natural gas is enough to supply over 100
years of use. Shale gas resource and production estimates increased
significantly between the 2010 and 2011 Outlook reports and are likely to
increase further in the future.
Where is Shale Gas Found?
Shale gas is found in shale
"plays," which are shale formations containing significant
accumulations of natural gas and which share similar geologic and
geographic properties. A decade of production has come from the Barnett
Shale play in Texas. Experience and information gained from developing the
Barnett Shale have improved the efficiency of shale gas development around
the country. Another important play is the Marcellus Shale in the eastern
United States. Surveyors and geologists identify suitable well locations
in areas with potential for economical gas production by using both
surface-level observation techniques and computer-generated maps of the
Global Shale Plays
Hydraulic fracturing is a technology that was developed in
the 1940s and has since helped produce more than 600 trillion cubic feet
of natural gas and 7 billion barrels of oil.
(commonly called “fracking” or “hydrofracking”) is a technique in
which water, chemicals, and sand are pumped into the well to unlock the
hydrocarbons trapped in shale formations by opening cracks (fractures) in
the rock and allowing natural gas to flow from the shale into the well.
When used in conjunction with horizontal drilling, hydraulic fracturing
enables gas producers to extract shale gas at reasonable cost. Without
these techniques, natural gas does not flow to the well rapidly, and
commercial quantities cannot be produced from shale.
How is Shale Gas
Production Different from Conventional Gas Production?
Conventional gas reservoirs
are created when natural gas migrates toward the Earth's surface from an
organic-rich source formation into highly permeable reservoir rock, where
it is trapped by an overlying layer of impermeable rock. In contrast,
shale gas resources form within the organic-rich shale source rock. The
low permeability of the shale greatly inhibits the gas from migrating to
more permeable reservoir rocks. Without horizontal drilling and hydraulic
fracturing, shale gas production would not be economically feasible
because the natural gas would not flow from the formation at high enough
rates to justify the cost of drilling.
The process of bringing a well to completion is generally
short-lived, taking a few months for a single well, after which the well
can be in production for 20 to 40 years. The process for a single
horizontal well typically includes four to eight weeks to prepare the site
for drilling, four or five weeks of rig work, including casing and
cementing and moving all associated auxiliary equipment off the well site
before fracturing operations commence, and two to five days for the entire
multi-stage fracturing operation.
Typically, steel pipe known as surface casing is cemented
into place at the uppermost portion of a well for the explicit purpose of
protecting the groundwater. The depth of the surface casing is generally
determined based on groundwater protection, among other factors. As the
well is drilled deeper, additional casing is installed to isolate the
formation(s) from which oil or natural gas is to be produced, which
further protects groundwater from the producing formations in the well.
Casing and cementing are critical parts of the well construction that not
only protect any water zones but are also important to successful oil or
natural gas production from hydrocarbon bearing zones.
Water is an
essential component of deep shale gas development during both the drilling
and hydraulic fracturing, or fracking, processes.
On the average
5 million gallons of water is needed to drill and fracture a typical deep
shale gas well is equivalent to the amount of water consumed by:
York City in approximately seven minutes
megawatt coal-fired power plant in 12 hours
golf course in 25 days
of corn in a season
What Are the Environmental
Issues Associated with Shale Gas?
contaminate water from spills or accidents.
Requires millions of
gallons of water, which can deplete local water supplies.
The processes may leave
behind waste containing concentrations of naturally-occurring
radioactive material (NORM) from the surrounding soils and rocks. Once
exposed or concentrated by human activity, this naturally-occurring
material becomes Technologically-Enhanced NORM or TENORM. Radioactive
materials are not necessarily present in the soils at every well or
drilling site. However in some areas of the country, such as the upper
Midwest or Gulf Coast states, the soils are more like to contain
Natural gas is
cleaner-burning than coal or oil. The combustion of natural gas emits
significantly lower levels of carbon dioxide (CO2), nitrogen
oxides, and sulfur dioxide than does the combustion of coal or oil. When
used in efficient combined-cycle power plants, natural gas combustion can
emit less than half as much CO2 as coal combustion, per unit of
However, there are some
potential environmental concerns that are also associated with the
production of shale gas. The fracturing of wells requires large amounts of
water. In some areas of the country, significant use of water for shale
gas production may affect the availability of water for other uses, and
can affect aquatic habitats.
Second, if mismanaged,
hydraulic fracturing fluid — which may contain potentially hazardous
chemicals — can be released by spills, leaks, or various other exposure
pathways. Any such releases can contaminate surrounding areas.
open fractures and allows gas / fluids to flow more freely to the
up perforation intervals of cement and drilling mud prior to
fracturing fluid injection, and provides accessible path to
acid (HCl, 3% to 28%) or muriatic acid
the viscosity of the fluid in order to release proppant into
fractures and enhance the recovery of the fracturing fluid.
growth of organisms that could produce gases (particularly hydrogen
sulfide) that could contaminate methane gas. Also prevents the
growth of bacteria which can reduce the ability of the fluid to
carry proppant into the fractures.
/ pH Adjusting Agent
and controls the pH of the fluid in order to maximize the
effectiveness of other additives such as crosslinkers.
or potassium carbonate; acetic acid
Stabilizer / Control
swelling and migration of formation clays which could block pore
spaces thereby reducing permeability.
rust formation on steel tubing, well casings, tools, and tanks (used
only in fracturing fluids that contain acid).
ammonium bisulfate for Oxygen Scavengers
fluid viscosity is increased using phosphate esters combined with
metals. The metals are referred to as crosslinking agents. The
increased fracturing fluid viscosity allows the fluid to carry more
proppant into the fractures.
hydroxide; borate salts
fracture fluids to be injected at optimum rates and pressures by
Finally, fracturing also
produces large amounts of wastewater, which may contain dissolved
chemicals and other contaminants that require treatment before disposal or
reuse. Because of the quantities of water used and the complexities
inherent in treating some of the wastewater components, treatment and
disposal is an important and challenging issue.
Credit: Energy Information
Administration, U.S. Department of Energy,CIA, American Gas Association,Chesapeake
compiled from The British Antarctic Study, NASA, Environment Canada,
UNEP, EPA and other sources as stated and credited Researched by Charles
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