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Last Updated: February 2009
Next Update: February 2010
Where does natural gas come from?
The most widely accepted theory about how natural gas was created is
that it was formed by the underground decomposition of organic matter
(dead plants and animals). If the organic matter is buried deeply enough,
much of the carbon and hydrogen is converted to methane, the major
component of natural gas. (The chemical formula for methane is CH4--that
is, a molecule of methane has one carbon atom and four hydrogen
atoms.)
Large volumes of methane can be trapped in the subsurface of the Earth
at places where the right geological conditions occurred at the right
times. Such a place is called a reservoir. Reservoirs are made up of porous and permeable rocks that can hold significant amounts of oil and gas within their pore spaces.
What are proved reserves?
Proved reserves of natural gas are estimated quantities
that analyses of geological and engineering data have demonstrated to be
economically recoverable in future years from known reservoirs. Drilling is typically required before reserves can be proved, but drilling is not typically associated with undiscovered resources that are described below.. Produced
natural gas placed in temporary underground storage is not included in
proved reserves.
Proved reserves are added each year with successful exploratory wells and as more is learned about fields where current wells are producing. For this reason those reserves constantly change and should not be considered a finite amount of resources available.
How much natural gas reserves are in the U.S.?
As of December 31, 2007, estimated proved reserves of dry natural gas
in the United States were 237,726 billion cubic feet (Bcf) and U.S. natural gas consumption was 23,242 Bcf in 2007. Dry natural
gas is the gas that remains after the economically liquefiable hydrocarbon
portion has been removed from the produced gas stream at a natural gas
processing plant.
Record-high additions to U.S. dry natural gas proved reserves in 2007 totaled 46.1 trillion cubic feet (Tcf), more than double the 19.5 Tcf of dry natural as actually produced during the year. The dry natural gas reserve additions mostly reflected the rapid development of unconventional gas resources including shale, coalbed methane, and tight low-permeability formations. Many of these unconventional resources are now economic to develop because of the application of advanced technologies like horizontal drilling with hydraulic fracturing. |
| Dry Natural Gas Proved Reserves by Area, 2007 |
click on image to enlarge
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| Source: Energy Information Administration, U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Reserves 2007 Annual Report |
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What are undiscovered recoverable resources?
In addition to proved natural gas reserves, there
are large volumes of natural gas classified as undiscovered recoverable
resources. Those resources are expected to exist because the geologic
settings are favorable. Over half of all onshore undiscovered gas
resources are located in the Alaska and Gulf Coast regions. Over one-third
of all undiscovered gas resources are estimated to be in Federal offshore
areas, primarily near Alaska, in the Gulf of Mexico, and along the
Atlantic Coast.
More information on this subject can be found in the following EIA publications:
 U.S.
Crude Oil, Natural Gas, and Natural Gas Liquids Reserves
Annual Energy Review
Natural Gas - A Fossil Fuel
Natural Gas Annual
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