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[[Image:Natural gas production world.PNG|thumb|450px|Natural gas extraction by countries in cubic meters per year.]]

'''Natural gas''' is a naturally occurring [[hydrocarbon]] [[gas]] mixture consisting primarily of [[methane]], with up to 20 %<ref>{{cite web|url=http://www.naturalgas.org/overview/background.asp |title=composition of natural gas |publisher=Naturalgas.org |date= |accessdate=2011-02-06}}</ref> of other hydrocarbons as well as impurities in varying amounts such as [[carbon dioxide]]. Natural gas is widely used as an important energy source in many applications including heating buildings, generating electricity, providing heat and power to industry, as fuel for vehicles and as a chemical feedstock in the manufacture of products such as [[plastics]] and other commercially important [[organic compound|organic chemicals]].

Natural gas is found in deep underground natural rock formations or associated with other hydrocarbon reservoirs, in [[coal bed]]s, and as [[methane clathrate]]s. Most natural gas was created over time by two mechanisms: biogenic and thermogenic. Biogenic gas is created by [[methanogen]]ic organisms in [[marsh]]es, [[bog]]s, [[landfill]]s, and shallow sediments. Deeper in the earth, at greater temperature and pressure, thermogenic gas is created from buried organic material.<ref>US Geological Survey, [http://energy.er.usgs.gov/gg/research/petroleum_origins.html Organic origins of petroleum]</ref><ref>US Energy Information Administration[http://www.eia.gov/energyexplained/index.cfm?page=natural_gas_home]</ref>

Before natural gas can be used as a fuel, it must undergo [[natural gas processing|processing]] to clean the gas and remove impurities including water in order to meet the specifications of marketable natural gas. The by-products of processing include [[ethane]], [[propane]], [[butane]]s, [[pentane]]s, and higher molecular weight [[hydrocarbon]]s, [[hydrogen sulphide]] (which may be converted into pure [[sulfur]]), [[carbon dioxide]], [[water vapor]], and sometimes [[helium]] and [[nitrogen]].

Natural gas is often informally referred to simply as '''gas''', especially when compared to other energy sources such as oil or coal.

==Sources==
{{See also|List of natural gas fields|List of countries by natural gas proven reserves|List of countries by natural gas production}}

===Natural gas===
[[File:BarnettShaleDrilling-9323.jpg|thumb|upright|Natural gas [[horizontal drilling|drilling]] [[drilling rig|rig]] in Texas.]]
In the 19th century, natural gas was usually obtained as a byproduct of [[Oil well|producing oil]], since the small, light gas carbon chains came out of solution as the extracted fluids underwent pressure reduction from the [[Petroleum reservoir|reservoir]] to the surface, similar to uncapping a bottle of soda pop where the carbon dioxide [[effervesce]]s. Unwanted natural gas was a disposal problem in the active oil fields. If there was not a market for natural gas near the [[wellhead]] it was virtually valueless since it had to be piped to the end user. In the 19th century and early 20th century, such unwanted gas was usually burned off in the oil fields. Today, unwanted gas (or [[stranded gas reserve|stranded gas]] without a market) associated with oil extraction often is returned to the reservoir with 'injection' wells while awaiting a possible future market or to repressurize the formation, which can enhance extraction rates from other wells. In regions with a high natural gas demand (such as the US), pipelines are constructed when economically feasible to move the gas from the wellsite to the [[end consumer]].

Another possibility is to export the natural gas as a [[LNG|liquid]]. [[Gas-to-liquids]] (GTL) is a developing technology that converts stranded natural gas into [[synthetic gasoline]], diesel, or jet fuel through the [[Fischer-Tropsch]] process developed during World War II by Germany. Such fuel can be transported to users through conventional pipelines and tankers. Proponents claim GTL burns cleaner than comparable petroleum fuels. Most major international oil companies are in an advanced stage of GTL production. A world-scale ({{convert|140000|oilbbl}} a day) [[Pearl GTL|GTL plant in Qatar]] went into production in 2011.

Natural gas can be "associated" (found in [[oil field]]s) or "non-associated" (isolated in [[natural gas field]]s), and is also found in [[coal bed]]s (as [[coalbed methane]]). It sometimes contains significant amounts of [[ethane]], [[propane]], [[butane]], and [[pentane]]—heavier hydrocarbons removed for commercial use prior to the [[methane]] being sold as a consumer fuel or chemical plant feedstock. Non-hydrocarbons such as [[carbon dioxide]], [[nitrogen]], [[helium]] (rarely), and [[hydrogen sulfide]] must also be removed before the natural gas can be transported.<ref>{{cite web|url=http://www.naturalgas.org/overview/background.asp |title=Natural gas overview |publisher=Naturalgas.org |date= |accessdate=2011-02-06}}</ref>

Natural gas is commercially extracted from [[oil field]]s and [[natural gas field]]s. Gas extracted from oil wells is called casinghead gas or associated gas. The natural gas industry is extracting gas from increasingly more challenging [[History of the petroleum industry in Canada (natural gas)#Unconventional gas|resource types]]: [[sour gas]], [[tight gas]], [[shale gas]], and [[coalbed methane]].

The world's largest proven gas reserves are located in [[Russia]], with 4.757{{e|13}} m³ (1.68{{e|15}} cubic feet). With the [[Gazprom]] company, Russia is frequently the world's largest natural gas extractor. Major proven resources (in billion cubic meters) are world 175,400 (2006), Russia 47,570 (2006), Iran 26,370 (2006), Qatar 25,790 (2007), Saudi Arabia 6,568 (2006) and United Arab Emirates 5,823 (2006).

It is estimated that there are about 900 trillion cubic meters of "unconventional" gas such as [[shale gas]], of which 180 trillion may be recoverable.<ref>[http://www.newscientist.com/article/mg20627641.100-wonderfuel-welcome-to-the-age-of-unconventional-gas.html?full=true "Wonderfuel: Welcome to the age of unconventional gas"] by Helen Knight, ''[[New Scientist]]'', 12 June 2010, pp. 44–7.</ref> In turn, many studies from [[MIT]], [[Black & Veatch]] and the [[United States Department of Energy|DOE]] -- see natural gas -- will account for a larger portion of electricity generation and heat in the future.<ref>Michael Kanellos, Greentechmedia. "[http://www.greentechmedia.com/articles/read/with-natural-gas-will-we-swap-oil-imports-for-gas-imports/ In Natural Gas, U.S. Will Move From Abundance to Imports]". 9 June 2011.</ref>

The world's largest gas field is [[Qatar]]'s offshore [[South Pars / North Dome Gas-Condensate field|North Field]], estimated to have 25 trillion cubic meters<ref>{{cite web|url=http://www.state.gov/r/pa/ei/bgn/5437.htm |title=Background note: Qatar |publisher=State.gov |date=2010-09-22 |accessdate=2011-02-06}}</ref> (9.0{{e|14}}<!--1500 needs reference-->cubic feet) of gas in place—enough to last more than 420 years{{Citation needed|date=January 2011}} at optimum extraction levels. The second largest natural gas field is the [[Asalouyeh|South Pars Gas Field]] in [[Iran]]ian waters in the [[Persian Gulf]]. Located next to Qatar's North Field, it has an estimated reserve of 8 to 14 trillion cubic meters<ref>{{cite web|url=http://www.pseez.ir/gas-en.html|publisher=Pars Special Economic Energy Zone|accessdate=2007-07-17|title=Pars Special Economic Energy Zone}}</ref> {{nowrap|(2.8{{e|14}} to 5.0{{e|14}} cubic feet)}} of gas.

Because natural gas is not a pure product, as the reservoir pressure drops when non-associated gas is extracted from a field under [[Supercritical fluid|supercritical]] (pressure/temperature) conditions, the higher molecular weight components may partially condense upon isothermic depressurizing—an effect called [[retrograde condensation]]. The liquid thus formed may get trapped as the pores of the gas reservoir get deposited. One method to deal with this problem is to re-inject dried gas free of condensate to maintain the underground pressure and to allow re-evaporation and extraction of condensates. More frequently, the liquid condenses at the surface, and one of the tasks of the [[Natural gas processing|gas plant]] is to collect this condensate. The resulting liquid is called natural gas liquid (NGL) and has commercial value.

===Town gas===
[[Town gas]], a synthetically produced mixture of methane and other gases, mainly the highly toxic [[carbon monoxide]], is used in a similar way to natural gas and can be produced by treating [[coal]] chemically. This is an historical technology, not usually economically competitive with other sources of fuel gas today. But there are still some specific cases where it is the best option and it may be so into the future.

Most town "gashouses" located in the eastern US in the late 19th and early 20th centuries were simple by-product [[coke (fuel)|coke]] ovens which heated bituminous coal in air-tight chambers. The gas driven off from the coal was collected and distributed through networks of pipes to residences and other buildings where it was used for cooking and lighting. (Gas heating did not come into widespread use until the last half of the 20th century.) The [[coal tar]] (or [[asphalt]]) that collected in the bottoms of the gashouse ovens was often used for roofing and other water-proofing purposes, and when mixed with sand and gravel was used for paving streets.

===Biogas===
{{main|biogas}}
When methane-rich gases are produced by the [[anaerobic decay]] of non-fossil [[organic compound|organic]] matter ([[biomass]]), these are referred to as biogas (or natural biogas). Sources of biogas include [[swamp]]s, [[marsh]]es, and [[landfill]]s (see [[landfill gas]]), as well as [[sewage]] [[sludge]] and [[manure]]<ref>{{cite web|url=http://www.manure.umn.edu/ |title=Manure Management and Air Quality at the University of Minnesota |publisher=Manure.umn.edu |date= |accessdate=2011-02-06}}</ref> by way of [[anaerobic digester]]s, in addition to [[enteric fermentation]], particularly in [[cattle]].

[[Methanogen|Methanogenic archaea]] are responsible for all biological sources of methane, some in symbiotic relationships with other life forms, including [[termite]]s, [[ruminant]]s, and cultivated crops. Methane released directly into the atmosphere would be considered a [[pollutant]]. However, methane in the atmosphere is oxidized, producing carbon dioxide and water. Methane in the atmosphere has a half life of seven years, meaning that if a tonne of methane were emitted today, 500 kilograms would have broken down to carbon dioxide and water after seven years.

[[Image:U.S. Natural Gas Production 1900-2005.png|left|thumb|350px|U.S. natural gas extraction, 1900–2005. Source: EIA.]]

Other sources of [[methane]], the principal component of natural gas, include [[landfill gas]], biogas, and [[methane hydrate]]. Biogas, and especially landfill gas, are already used in some areas, but their use could be greatly expanded. Landfill gas is a type of biogas, but biogas usually refers to gas produced from organic material that has not been mixed with other waste.

[[Landfill gas]] is created from the decomposition of waste in [[landfill]]s. If the gas is not removed, the pressure may get so high that it works its way to the surface, causing damage to the landfill structure, unpleasant odor, vegetation die-off, and an [[explosion]] hazard. The gas can be vented to the atmosphere, [[gas flare|flared]] or burned to produce [[electricity]] or [[heat]]. Experimental systems were being proposed for use in parts of [[Hertfordshire]], UK, and [[Lyon]] in France.

Once [[water vapor]] is removed, about half of landfill gas is methane. Almost all of the rest is [[carbon dioxide]], but there are also small amounts of [[nitrogen]], [[oxygen]], and [[hydrogen]]. There are usually trace amounts of [[hydrogen sulfide]] and [[siloxane]]s, but their concentration varies widely. Landfill gas cannot be distributed through utility natural gas pipelines unless it is cleaned up to less than 3% {{CO2}}, and a few parts per million {{chem|H|2|S}}, because {{CO2}} and {{chem|H|2|S}} corrode the pipelines.<ref>{{cite web|url=http://www.beg.utexas.edu/energyecon/lng/documents/CEE_Interstate_Natural_Gas_Quality_Specifications_and_Interchangeability.pdf |title=Interstate Natural Gas--Quality Specifications Interchangeability White Paper With Exhibits|format=PDF |date= |accessdate=2011-02-06}}</ref> It is usually more economical to combust the gas on site or within a short distance of the landfill using a dedicated pipeline. Water vapor is often removed, even if the gas is combusted on site. If low temperatures condense water out of the gas, [[siloxanes]] can be lowered as well because they tend to condense out with the water vapor. Other non-methane components may also be removed in order to meet [[emission standard]]s, to prevent fouling of the equipment or for environmental considerations. Co-firing landfill gas with natural gas improves combustion, which lowers emissions.

Gas generated in [[sewage treatment]] plants is commonly used to generate electricity. For example, the Hyperion sewage plant in Los Angeles burns {{convert|8|e6cuft|m3}} of gas per day to generate power<ref>{{cite web|url=http://www.lasewers.org/treatment_plants/hyperion/index.htm |title=LA Sewers |publisher=LA Sewers |date= |accessdate=2011-02-06}}</ref> New York City utilizes gas to run equipment in the sewage plants, to generate electricity, and in boilers.<ref>{{cite web|url=http://www.nyc.gov/html/dep/pdf/wwsystem.pdf |title=WastewaterInsides-05 |format=PDF |date= |accessdate=2011-02-06}}</ref> Using sewage gas to make electricity is not limited to large cities. The city of [[Bakersfield, California]], uses [[cogeneration]] at its sewer plants.<ref>{{cite web|url=http://www.parsons.com/projects/Pages/bakersfield-wwtp-3.aspx |title=Bakersfield Wastewater Treatment Plant 3 |publisher=Parsons.com |date=2009-12-05 |accessdate=2011-02-06}}</ref> California has 242 sewage wastewater treatment plants, 74 of which have installed anaerobic digesters. The total biopower generation from the 74 plants is about 66 MW.<ref>http://www.energy.ca.gov/2010publications/CEC-500-2010-007/CEC-500-2010-007.PDF</ref>

[[Biogas]] is usually produced using [[agricultural waste]] materials, such as otherwise unusable parts of plants and [[manure]]. Biogas can also be produced by separating [[organic material]]s from waste that otherwise goes to landfills. This method is more efficient than just capturing the landfill gas it produces. Using materials that would otherwise generate no income, or even cost money to get rid of, improves the profitability and energy balance of biogas production.

[[Anaerobic lagoon]]s produce biogas from manure, while biogas reactors can be used for manure or plant parts. Like landfill gas, biogas is mostly methane and carbon dioxide, with small amounts of nitrogen, oxygen and hydrogen. However, with the exception of pesticides, there are usually lower levels of contaminants.

[[Image:NaturalGasProcessingPlant.jpg|thumb|The McMahon natural gas processing plant in [[Taylor, British Columbia]], [[Canada]].<ref>http://www.naturalgas.org/images/McMahon-Plnt.jpg on http://www.naturalgas.org/naturalgas/processing_ng.asp</ref>]]

===Crystallized natural gas — hydrates===
Huge quantities of natural gas (primarily methane) exist in the form of [[methane clathrate|hydrates]] under sediment on offshore continental shelves and on land in arctic regions that experience [[permafrost]], such as those in [[Siberia]]. Hydrates require a combination of high pressure and low temperature to form. However, {{As of|2010|lc=on}} no technology has been developed yet to extract natural gas economically from hydrates.

In 2010, using current technology, the cost of extracting natural gas from crystallized natural gas is estimated to 100–200% the cost of extracting natural gas from conventional sources, and even higher from offshore deposits.<ref>{{cite web|author=By Steve Hargreaves, staff writer |url=http://money.cnn.com/2010/03/09/news/economy/nat_gas_crystals/index.htm |title=Fortune Magazine – Frozen Natural Gas in Indian Ocean |publisher=Money.cnn.com |date=2010-03-09 |accessdate=2011-02-06}}</ref>

==Natural gas processing==
{{Main|Natural gas processing}}

The image below is a schematic [[Process flow diagram|block flow diagram]] of a typical natural gas processing plant. It shows the various unit processes used to convert raw natural gas into sales gas pipelined to the end user markets.

The block flow diagram also shows how processing of the raw natural gas yields byproduct sulfur, byproduct ethane, and natural gas liquids (NGL) propane, butanes and natural gasoline (denoted as [[pentanes]] +).<ref>{{cite web|url=http://www.eia.doe.gov/pub/oil_gas/natural_gas/feature_articles/2006/ngprocess/ngprocess.pdf |title=Natural Gas Processing: The Crucial Link Between Natural Gas Production and Its Transportation to Market |format=PDF |date= |accessdate=2011-02-06}}</ref><ref>{{cite web|url=http://www.uop.com/gasprocessing/6070.html |title='&#39;Example Gas Plant'&#39; |publisher=Uop.com |date= |accessdate=2011-02-06}}</ref><ref>{{cite web|url=http://www.axens.net/upload/presentations/fichier/axens_gpagcc_2004v2.pdf |title='&#39;From Purification to Liquefaction Gas Processing'&#39; |format=PDF |date= |accessdate=2011-02-06}}</ref><ref>[http://www.spe.org/specma/binary/files/5804785Syn10682.pdf ''Feed-Gas Treatment Design for the Pearl GTL Project'']{{dead link|date=February 2011}}</ref><ref>[http://lnglicensing.conocophillips.com/NR/rdonlyres/B78B6727-E5F4-4505-B9C3-96CC94D7B30D/7357/AICHELNGNGLIntegrationPaper.pdf ''Benefits of integrating NGL extraction and LNG liquefaction'']{{dead link|date=February 2011}}</ref>

[[Image:NatGasProcessing.svg|frame|center|Schematic flow diagram of a typical natural gas processing plant.]]

==Depletion==
See main article, [[Gas depletion]]

==Uses==
===Power generation===
Natural gas is a major source of [[electricity generation]] through the use of [[gas turbine]]s and [[steam turbine]]s. Most grid [[peaking power plant]]s and some off-grid [[engine-generator]]s use natural gas. Particularly high efficiencies can be achieved through combining gas turbines with a steam turbine in [[combined cycle]] mode. Natural gas burns more cleanly than other [[hydrocarbon fuel]]s, such as oil and coal, and produces less carbon dioxide per unit of energy released. For an equivalent amount of heat, burning natural gas produces about 30% less [[carbon dioxide]] than burning [[petroleum]] and about 45% less than burning [[coal]].<ref name=gasdotorg>{{cite web|url=http://www.naturalgas.org/environment/naturalgas.asp#greenhouse/ |title=Natural Gas and the Environment |publisher=Naturalgas.org |date= |accessdate=2011-02-06}}</ref> Combined cycle power generation using natural gas is thus the cleanest source of power available using hydrocarbon fuels, and this technology is widely used wherever gas can be obtained at a reasonable cost. [[Fuel cell]] technology may eventually provide cleaner options for converting natural gas into electricity, but as yet it is not price-competitive.

===Domestic use===
{{Globalize/US|date=December 2010}}
Natural gas dispensed from a simple stovetop can generate heat in excess of 2000°F (1093°C) making it a powerful domestic cooking and heating fuel.<ref>{{Cite book
|title=Nature's curiosity shop
|last=Zimmerman
|first=Barry E.
|authorlink=
|last2=Zimmerman
|first2=David J.
|editorn-last=
|editorn-first=
|edition=
|volume=
|year=1995
|origyear=
|page=28
|pages=
|publisher=Contemporary books
|place=Lincolnwood (Chicago), IL
|url=
|accessdate=
|isbn=978-0809236565
|oclc=
}}</ref> In much of the developed world it is supplied to homes via pipes where it is used for many purposes including natural gas-powered ranges and ovens, natural gas-heated [[clothes dryer]]s, [[HVAC|heating]]/[[air conditioning|cooling]], and [[central heating]]. Home or other building heating may include boilers, [[furnace]]s, and [[water heater]]s. [[Compressed natural gas]] (CNG) is used in [[rural]] homes without connections to [[plumbing|pipe]]d-in [[public utility]] services, or with portable [[Grill (cooking)|grill]]s. Natural gas is also supplied by independent natural gas suppliers through [[Natural Gas Choice]] programs throughout the United States. However, due to CNG being less economical than [[Liquefied petroleum gas|LPG]], LPG (propane) is the dominant source of rural gas.

[[Image:WMATA 3006.jpg|thumb|A [[Washington, D.C.]] [[Metrobus (Washington, D.C.)|Metrobus]], which runs on natural gas.]]

===Transportation===
CNG is a cleaner alternative to other [[automobile]] fuels such as [[gasoline]] (petrol) and [[Diesel fuel|diesel]]. As of 2008 there were 9.6 million [[natural gas vehicle]]s worldwide, led by [[Pakistan]] (2.0 million), [[Argentina]] (1.7 million), [[Brazil]] (1.6 million), [[Iran]] (1.0 million), and [[India]] (650,000).<ref>{{cite web|url=http://www.iangv.org/tools-resources/statistics.html|title=Natural Gas Vehicle Statistics|publisher=International Association for Natural Gas Vehicles|date= |accessdate=2009-10-19}}</ref><ref name="GreenCar">{{cite web|url=http://www.greencarcongress.com/2009/10/forecast-17m-natural-gas-vehicles-worldwide-by-2015.html#more|title=Forecast: 17M Natural Gas Vehicles Worldwide by 2015|author=Pike Research|date=2009-10-19|publisher=[[Green Car Congress]]|accessdate=2009-10-19}}</ref> The energy efficiency is generally equal to that of gasoline engines, but lower compared with modern diesel engines. Gasoline/petrol vehicles converted to run on natural gas suffer because of the low [[compression ratio]] of their engines, resulting in a cropping of delivered power while running on natural gas (10%–15%). CNG-specific engines, however, use a higher compression ratio due to this fuel's higher [[octane number]] of 120–130.<ref>[http://www.imrt.ethz.ch/research/engine/CNG/cev Clean Engine Vehicle]{{dead link|date=February 2011}}, Measurement and Control Laboratory</ref>

===Fertilizers===
Natural gas is a major feedstock for the production of [[ammonia]], via the [[Haber process]], for use in [[fertilizer]] production.

===Aviation===
[[Russia]]n aircraft manufacturer [[Tupolev]] is currently running a development program to produce LNG- and [[hydrogen]]-powered aircraft.<ref>{{cite web|url=http://www.tupolev.ru/English/Show.asp?SectionID=82&Page=1 |title=PSC Tupolev – Development of Cryogenic Fuel Aircraft |publisher=Tupolev.ru |date= |accessdate=2011-02-06}}</ref> The program has been running since the mid-1970s, and seeks to develop LNG and hydrogen variants of the [[Tupolev Tu-204|Tu-204]] and [[Tupolev Tu-334|Tu-334]] passenger aircraft, and also the [[Tupolev Tu-330|Tu-330]] cargo aircraft. It claims that at current market prices, an LNG-powered aircraft would cost 5,000 [[rouble]]s (~ $218/ £112) less to operate per ton, roughly equivalent to 60%, with considerable reductions to [[carbon monoxide]], [[hydrocarbon]] and [[nitrogen oxide]] emissions.

The advantages of liquid methane as a jet engine fuel are that it has more specific energy than the standard [[kerosene]] mixes do and that its low temperature can help cool the air which the engine compresses for greater volumetric efficiency, in effect replacing an [[intercooler]]. Alternatively, it can be used to lower the temperature of the exhaust.

===Hydrogen===
Natural gas can be used to produce [[hydrogen]], with one common method being the [[hydrogen reformer]]. Hydrogen has many applications: it is a primary feedstock for the chemical industry, a hydrogenating agent, an important commodity for oil refineries, and the fuel source in [[hydrogen vehicle]]s.

===Other===
Natural gas is also used in the manufacture of [[textile|fabric]]s, [[glass]], [[steel]], [[plastic]]s, [[paint]], and other products.

==Storage and transport==
[[Image:Polyethylene gas main.jpg|thumb|upright|[[Polyethylene]] plastic [[Gas main|main]] being placed in a [[trench]].]]

Because of its low density, it is not easy to store natural gas or transport by vehicle. Natural gas [[pipeline transport|pipelines]] are impractical across [[ocean]]s. Many [[List of natural gas pipelines#North America|existing pipelines in America]] are close to reaching their capacity, prompting some politicians representing northern states to speak of potential shortages. In [[Europe]], the gas pipeline network is already dense in the West.<ref>[http://www.gie.eu.com/ Gas Infrasturcture Europe]. Retrieved 18 June. 2009.</ref> New pipelines are planned or under construction in Eastern Europe and between gas fields in [[Russia]], [[Near East]] and [[Northern Africa]] and Western Europe. See also [[List of natural gas pipelines]].

[[LNG carrier]]s transport [[liquefied natural gas]] (LNG) across oceans, while [[tank truck]]s can carry liquefied or [[compressed natural gas]] (CNG) over shorter distances. Sea transport using [[CNG carrier]] ships that are now under development may be competitive with LNG transport in specific conditions.

Gas is turned into liquid at a [[liquefaction of gases|liquefaction]] plant, and is returned to gas form at [[gasification|regasification]] plant at the [[LNG terminal|terminal]]. Shipborne regasification equipment is also used. LNG is the preferred form for long distance, high volume transportation of natural gas, whereas pipeline is preferred for transport for distances up to 4,000&nbsp;km over land and approximately half that distance offshore.

CNG is transported at high pressure, typically above 200 [[bar (unit)|bars]]. Compressors and decompression equipment are less capital intensive and may be economical in smaller unit sizes than liquefaction/regasification plants. Natural gas trucks and carriers may transport natural gas directly to end-users, or to distribution points such as pipelines.

[[Image:Manlove gas storage facility crop.jpg|thumb|left|[[Peoples Gas]] Manlove Field [[natural gas storage]] area in [[Newcomb Township, Champaign County, Illinois]]. In the foreground (left) is one of the numerous wells for the underground storage area, with an LNG plant, and above ground storage tanks are in the background (right).]]

In the past, the natural gas which was recovered in the course of recovering [[petroleum]] could not be profitably sold, and was simply burned at the oil field in a process known as [[gas flare|flaring]]. Flaring is now illegal in many countries.<ref>{{cite book|last=Hyne|first=Norman J. |title=Dictionary of petroleum exploration, drilling & production|publisher=PennWell Books|location=pg. 190|year=1991|page=625|isbn=0878143521}}</ref> Additionally, companies now recognize that gas may be sold to consumers in the form of LNG or CNG, or through other transportation methods. The gas is now re-[[Wiktionary:inject|inject]]ed into the formation for later recovery. The re-injection also assists oil pumping by keeping underground pressures higher.

A "master gas system" was invented in [[Saudi Arabia]] in the late 1970s, ending any necessity for flaring. Satellite observation, however, shows that flaring<ref>{{cite web|url=http://www.ethanzuckerman.com/blog/wp-content/2007/11/flares.jpg |title=Satellite observation of flares in the world |date= |accessdate=2011-02-06}}</ref> and venting<ref>Satellite observation of [[Methane#Methane in Earth's atmosphere|methane in earth's atmosphere]]</ref> are still practiced in some gas-extracting countries.

Natural gas is used to generate electricity and heat for [[desalination]]. Similarly, some landfills that also discharge methane gases have been set up to capture the methane and generate electricity.

Natural gas is often stored underground inside depleted gas reservoirs from previous gas wells, [[salt domes]], or in tanks as [[liquefied natural gas]]. The gas is injected in a time of low demand and extracted when demand picks up. Storage nearby end users helps to meet volatile demands, but such storage may not always be practicable.

With 15 countries accounting for 84% of the worldwide extraction, access to natural gas has become an important issue in international politics, and countries vie for control of pipelines.<ref>{{cite web|url=http://www.imi-online.de/2007.php3?id=1589 |title=The Contours of the New Cold War |publisher=Imi-online.de |date= |accessdate=2011-02-06}}</ref> In the first decade of the 21st century, [[Gazprom]], the state-owned energy company in Russia, engaged in disputes with [[Ukraine]] and [[Belarus]] over the price of natural gas, which have created concerns that gas deliveries to parts of Europe could be cut off for political reasons.<ref>{{cite web|url=http://www.npr.org/templates/story/story.php?storyId=99026745 |title=Gazprom and Russian Foreign Policy |publisher=Npr.org |date= |accessdate=2011-02-06}}</ref>

[[FLNG|Floating Liquefied Natural Gas (FLNG)]] is an innovative technology designed to enable the development of offshore gas resources that would otherwise remain untapped because due to environmental or economic factors it is nonviable to develop them via a land-based LNG operation. FLNG technology also provides a number of environmental and economic advantages:

* Environmental – Because all processing is done at the gas field, there is no requirement for long pipelines to shore, compression units to pump the gas to shore, dredging and jetty construction, and onshore construction of an LNG processing plant, which significantly reduces the environmental footprint.<ref>[http://www.seaaoc.com/news-old/shell-receives-green-light-for-prelude-flng Shell receives green light for Prelude FLNG — SEAAOC 2011<!-- Bot generated title -->]</ref> Avoiding construction also helps preserve marine and coastal environments. In addition, environmental disturbance will be minimised during decommissioning because the facility can easily be disconnected and removed before being refurbished and re-deployed elsewhere.

* Economic – Where pumping gas to shore can be prohibitively expensive, FLNG makes development economically viable. As a result, it will open up new business opportunities for countries to develop offshore gas fields that would otherwise remain stranded, such as those offshore East Africa.<ref>[http://www.visiongain.com/Report/568/The-Floating-Liquefied-Natural-Gas-(FLNG)-Market-2011-2021 The Floating Liquefied Natural Gas (FLNG) Market 2011-2021 - Report - Energy - visiongain<!-- Bot generated title -->]</ref>

Many gas and oil companies are considering the economic and environmental benefits of [[FLNG|Floating Liquefied Natural Gas (FLNG)]]. However, for the time being, the only FLNG facility now in development is being built by Shell,<ref>[http://www.platts.com/weblog/oilblog/2011/03/31/shell_australia.html Shell Australia upbeat on Prelude LNG; focus now turns to Timor - The Barrel<!-- Bot generated title -->]</ref> due for completion around 2017.<ref>[http://www.ft.com/cms/s/0/9ccaed4a-82ba-11e0-b97c-00144feabdc0.html#axzz1NADgzzOH FT.com / Companies / Oil & Gas - Shell’s floating LNG plant given green light<!-- Bot generated title -->]</ref>

==Environmental effects==
{{See also|Environmental issues with energy}}

===CO<sub>2</sub> emissions===
Natural gas is often described as the cleanest fossil [[fuel]], producing less carbon dioxide per [[joule]] delivered than either coal or oil<ref name=gasdotorg/> and far fewer pollutants than other hydrocarbon fuels{{Citation needed|date=November 2011}}. However, in absolute terms, it does contribute substantially to global [[carbon emission]]s, and this contribution is projected to grow. According to the [[IPCC Fourth Assessment Report]] (Working Group III Report, chapter 4), in 2004, natural gas produced about 5.3 billion tons a year of CO<sub>2</sub> emissions, while coal and oil produced 10.6 and 10.2 billion tons respectively (figure 4.4). According to an updated version of the [[Special Report on Emissions Scenarios#B2|SRES B2]] [[emissions scenario]], however, by the year 2030, natural gas would be the source of 11 billion tons a year, with coal and oil now 8.4 and 17.2 billion respectively because demand is increasing 1.9% a year.<ref>http://www.ipcc.ch/ipccreports/ar4-wg3.htm</ref> ([[List of countries by carbon dioxide emissions|Total global emissions]] for 2004 were estimated at over 27,200 million tons.)

In addition, natural gas itself is a [[greenhouse gas]] more potent than carbon dioxide. Although natural gas is released into the atmosphere in much smaller quantities, methane is oxidized in the atmosphere, and hence natural gas affects the atmosphere for approximately 12 years, compared to CO<sub>2</sub>, which is already oxidized, and has effect for 100 to 500 years. Natural gas is composed mainly of methane, which has a [[radiative forcing]] twenty times greater than carbon dioxide. Based on such composition, a ton of methane in the atmosphere traps as much radiation as 20 tons of carbon dioxide; however, it remains in the atmosphere for 8–40 times less time. Carbon dioxide still receives the lion's share of attention concerning greenhouse gases because it is released in much larger amounts. Still, it is inevitable when natural gas is used on a large scale that some of it will leak into the atmosphere. (Coal methane not captured by [[coal bed methane extraction]] techniques is simply lost into the atmosphere. Current estimates by the EPA place global emissions of methane at {{convert|3|e12cuft|km3}} annually,<ref>{{cite news|url=http://www.nytimes.com/2009/10/15/business/energy-environment/15degrees.html?_r=2&hpw |title=Curbing Emissions by Sealing Gas Leaks |publisher=nytimes.com |date=2009-10-15 |accessdate=2011-02-06}}</ref> or 3.2% of global production.<ref>{{cite web|url=http://www.wolframalpha.com/input/?i=world+natural+gas+production |title=Wolfram Alpha query: "World Natural Gas Production" |publisher=Wolframalpha.com |date= |accessdate=2011-02-06}}</ref> Direct emissions of methane represented 14.3% of all global anthropogenic greenhouse gas emissions in 2004.<ref>{{cite web|url=http://www.epa.gov/climatechange/economics/international.html |title=US EPA: Climate Economics |publisher=Epa.gov |date=2006-06-28 |accessdate=2011-02-06}}</ref>

===Other pollutants===
Natural gas produces far lower amounts of [[sulfur dioxide]] and [[nitrous oxide]]s than any other hydrocarbon fuel (fossil fuels).<ref>http://www.nbr.org/downloads/pdfs/eta/PES_2011_Herberg.pdf Natural Gas in Asia: History and Prospects by Mikkal Herberg (written for 2011 Pacific Energy Summit</ref> [[Carbon dioxide]] produced is 117,000 ppm vs 208,000 for burning coal. [[Carbon monoxide]] produced is 40 ppm vs 208 for burning coal{{Citation needed|date=August 2011}}. [[Nitrogen oxide]]s produced is 92 ppm vs 457 for burning coal. Sulfur dioxide is 1 ppm vs 2,591 for burning coal. [[Mercury (element)|Mercury]] is 0 vs .016 for burning coal.<ref>{{cite web|url=http://www.global-greenhouse-warming.com/gas-vs-coal.html |title="Gas vs Coal" |publisher=Global-greenhouse-warming.com |date= |accessdate=2011-02-06}}</ref> Particulates are also a major contribution to global warming. Natural gas has 7ppm vs coal's 2,744ppm.<ref>{{cite web|url=http://www.physicalgeography.net/fundamentals/7h.html |title='&#39;Fundamentals of Physical Geography (2nd Edition)'&#39;, "Chapter 7: Introduction to the Atmosphere," (h). "The Greenhouse Effect" |publisher=Physicalgeography.net |date= |accessdate=2011-02-06}}</ref> Natural gas also has [[Radon]], from 5 to 200,000 [[Becquerels]] per cubic meter. <ref>{{cite web|url=http://world-nuclear.org/info/inf30.html |title='Naturally Occurring Radioactive Materials' |publisher='World Nuclear Association' |date= |accessdate=2012-01-31}}</ref>

===Extraction===
The practice of hydraulic fracturing, the process of using a combination of chemicals ranging from harmless to toxic to force natural gas to the surface from reservoirs with low permeability, has come under scrutiny internationally due to concerns about environmental and health safety, and has been suspended or banned in some countries. See also: [[Hydraulic_fracturing#Environmental_Concerns|''Environmental concerns with hydraulic fracturing'']]

==Safety concerns==
[[Image:Gas pipeline odourant injection facility.JPG|thumb|A pipeline odorant injection station]]

===Production===
In [[mining|mine]]s, where methane seeping from rock formations has no odor, [[sensor]]s are used, and mining apparatus such as the [[Davy lamp]] has been specifically developed to avoid ignition sources.

Some gas fields yield [[sour gas]] containing [[hydrogen sulfide]] (H<sub>2</sub>S). This untreated gas is [[toxic]]. [[Amine gas treating]], an industrial scale process which removes [[acidic]] [[gas]]eous components, is often used to remove hydrogen sulfide from natural gas.<ref>{{cite web|url=http://www.naturalgas.org/naturalgas/processing_ng.asp |title=Processing Natural Gas |publisher=NaturalGas.org |date= |accessdate=2011-02-06}}</ref>

Extraction of natural gas (or oil) leads to decrease in pressure in the [[oil reservoir|reservoir]]. Such decrease in pressure in turn may result in [[subsidence]], sinking of the ground above. Subsidence may affect ecosystems, waterways, sewer and water supply systems, foundations, and so on.

Another ecosystem effect results from the noise of the process. This can change the composition of animal life in the area, and have consequences for plants as well in that animals disperse seeds and pollen.

Releasing the gas from low-permeability reservoirs is accomplished by a process called [[hydraulic fracturing]] or "hydrofracking". To allow the natural gas to flow out of the shale, oil operators force 1 to {{convert|9|e6USgal|m3}} of water mixed with a variety of chemicals through the wellbore casing into the shale. The high pressure water breaks up or "fracks" the shale, which releases the trapped gas. Sand is added to the water as a proppant to keep the fractures in the shale open, thus enabling the gas to flow into the casing and then to the surface. The chemicals are added to the frack fluid to reduce friction and combat corrosion. During the extracting life of a gas well, other low concentrations of other chemical substances may be used, such as biocides to eliminate fouling, scale and corrosion inhibitors, oxygen scavengers to remove a source of corrosion, and acids to clean the perforations in the pipe.

Dealing with fracking fluid can be a challenge. Along with the gas, 30% to 70% of the chemically-laced frack fluid, or flow back, returns to the surface. Additionally, a significant amount of salt and other minerals, once a part of the rock layers that were under prehistoric seas, may be incorporated in the flow back as they dissolve in the frack fluid.

===Use===
In order to assist in detecting [[leak]]s, a minute amount of [[aroma compound|odorant]] is added to the otherwise colorless and almost odorless gas used by consumers. The odor has been compared to the smell of rotten eggs, due to the added [[Butanethiol|butyl mercaptan]]. Sometimes a related compound, [[tetrahydrothiophene|thiophane]] may be used in the mixture. Situations in which an odorant that is added to natural gas can be detected by analytical instrumentation, but cannot be properly detected by an observer with a normal sense of smell, have occurred in the natural gas industry. This is caused by odor masking, when one odorant overpowers the sensation of another. As of 2011, the industry is conducting research on the causes of odor masking. <ref> [http://nvlpubs.nist.gov/nistpubs/jres/116/6/V116.N06.A05.pdf “Findings and Recommendations From the Joint NIST—AGA Workshop on Odor Masking”]. Nancy Rawson, Ali Quraishi, Thomas J. Bruno. Journal of Research of the National Institute of Standards and Technology, Vol. 116, No. 6, Pgs. 839-848. Nov-Dec 2011.</ref>

[[File:Fire engines in Kiev, Ukraine.JPG|thumb|Gas network emergency vehicle responding to a major fire in [[Kiev]], [[Ukraine]]]]
Explosions caused by natural [[gas leak]]s occur a few times each year. Individual homes, small businesses and other structures are most frequently affected when an internal leak builds up gas inside the structure. Frequently, the blast will be enough to significantly damage a building but leave it standing. In these cases, the people inside tend to have minor to moderate injuries. Occasionally, the gas can collect in high enough quantities to cause a deadly explosion, disintegrating one or more buildings in the process. The gas usually dissipates readily outdoors, but can sometimes collect in dangerous quantities if flow rates are high enough. However, considering the tens of millions of structures that use the fuel, the individual risk of using natural gas is very low.

Natural gas heating systems are a minor source of [[carbon monoxide]] deaths in the United States. According to the US Consumer Product Safety Commission (2008), 56% of unintentional deaths from non-fire CO poisoning were associated with engine-driven tools like gas-powered generators and lawn mowers. Natural gas heating systems accounted for 4% of these deaths. Improvements in natural gas furnace designs have greatly reduced CO poisoning concerns. [[Carbon monoxide detector|Detectors]] are also available that warn of carbon monoxide and/or explosive gas (methane, propane, etc.).

==Energy content, statistics, and pricing==
{{Main|Natural gas prices}}
{{see also|Billion cubic metres of natural gas}}
[[Image:Henry hub NG prices.svg|thumb|right|300px|[[Natural gas prices]] at the [[Henry Hub]] in US dollars per million BTUs ($/mmbtu) for 2000–2010.]]
Quantities of natural gas are measured in [[normal cubic meter]]s (corresponding to 0 °C at 101.325 [[atmosphere (unit)|kPa]]) or in [[standard cubic feet]] (corresponding to {{convert|60|°F|°C|abbr=on}} and 14.73 [[pounds per square inch|psia]]).
The [[higher heating value|gross heat of combustion]] of one cubic meter of commercial quality natural gas is around 39&nbsp;[[joule|megajoule]]s (≈10.8&nbsp;[[kWh]]), but this can vary by several percent. This comes to about 49&nbsp;[[joule|megajoule]]s (≈13.5&nbsp;[[kWh]]) for one kg of natural gas (assuming 0.8&nbsp;kg/m^3, an approximate value).{{cn|date=December 2011}}

The price of natural gas varies greatly depending on location and type of consumer. In 2007, a price of $7 per {{convert|1000|cuft|m3}} was typical in the United States. The typical caloric value of natural gas is roughly 1,000 [[British thermal unit]]s (BTU) per cubic foot, depending on gas composition. This corresponds to around $7 per million BTU, or around $7 per [[gigajoule]]. In April 2008, the wholesale price was $10 per {{convert|1000|cuft|m3}} ($10/MMBTU).<ref>{{cite web|author=James L. Williams |url=http://www.wtrg.com/daily/gasprice.html |title=Graph of Natural Gas Futures Prices – NYMEX |publisher=Wtrg.com |date=1998-10-02 |accessdate=2011-02-06}}</ref> The residential price varies from 50% to 300% more than the wholesale price. At the end of 2007, this was $12–$16 per {{convert|1000|cuft|m3|abbr=on}}.<ref>{{cite web|url=http://tonto.eia.doe.gov/dnav/ng/ng_pri_sum_dcu_nus_m.htm |title=Natural Gas Prices published by the US government |publisher=Tonto.eia.doe.gov |date= |accessdate=2011-02-06}}</ref> Natural gas in the United States is traded as a [[futures contract]] on the [[New York Mercantile Exchange]]. Each contract is for 10,000 MMBTU (~10,550 [[gigajoule]]s), or 10 billion BTU. Thus, if the price of gas is $10 per million BTUs on the NYMEX, the contract is worth $100,000.

===European Union===
As one of the world's largest importers of natural gas, the EU is a major player on the international gas market.

Gas prices for end users vary greatly across the EU.<ref>[http://www.energy.eu/#Domestic EU Gas Prices]</ref> A single European energy market, one of the key objectives of the European Union, should level the prices of gas in all EU member states.

===United States===
In [[United States customary units|US units]], one [[standard cubic foot]] of natural gas produces around 1,028&nbsp;[[British thermal unit]]s (BTU). The actual heating value when the water formed does not condense is the [[lower heating value|net heat of combustion]] and can be as much as 10% less.<ref>[http://www.webcitation.org/5nhzCic1h Heat value definitions]. WSU website. Retrieved 2008-05-19.</ref>

In the United States, retail sales are often in units of [[therm]]s (th); 1 therm = 100,000&nbsp;BTU. [[Gas meter]]s measure the volume of gas used, and this is converted to therms by multiplying the volume by the energy content of the gas used during that period, which varies slightly over time. Wholesale transactions are generally done in [[decatherm]]s (Dth), or in thousand decatherms (MDth), or in million decatherms (MMDth). A million decatherms is roughly a billion cubic feet of natural gas. Gas sales to domestic consumers may be in units of 100 standard cubic feet ([[Standard cubic foot|Ccf]]).

As of 2009, the Potential Gas Committee estimated that the United States has total future recoverable natural gas resources approximately 100 times greater than current annual consumption.<ref>Potential Gas Committee, [http://www.aga.org/Newsroom/news-releases/2009/Pages/NewReportFindsUnprecedented.aspx ''Potential Gas Committee reports unprecedented increase in magnitude of U.S. natural gas resource base''], 18 June 2009. Retrieved 2011-06-25.</ref>

===Canada===
Canada uses [[metric units|metric]] measure for internal trade of petrochemical products. Consequently, natural gas is sold by the [[Joule#Gigajoule|Gigajoule]], a measure approximately equal to 1/2 of a barrel (250lbs) of oil, or 1 million BTUs, or 1000 cu ft of gas, or 28cu metres of gas.

===Elsewhere===
In the rest of the world, natural gas is sold in [[Joule#Gigajoule|Gigajoule]] retail units. LNG ([[liquefied natural gas]]) and LPG ([[liquefied petroleum gas]]) are traded in metric tons or mmBTU as spot deliveries. Long term natural gas distribution contracts are signed in cubic metres, and LNG contracts are in metric tonnes (1,000kg). The LNG and LPG is transported by specialized [[LNG carrier|transport ships]], as the gas is liquified at [[cryogenic]] temperatures. The specification of each LNG/LPG cargo will usually contain the energy content, but this information is in general not available to the public.

In the Russian Federation, [[Gazprom]] sold approximately 250 billion cubic metres of natural gas in 2008.

==See also==
{{Portal box|Sustainable development|Energy}}
{{div col|colwidth=20em}}
*[[Associated petroleum gas]]
*[[Drip gas]]
*[[Energy development]]
*[[Gas oil ratio]]
*[[Giant oil and gas fields]]
*[[Hydraulic fracturing]]
*[[Natural gas by country]]
*[[Peak gas]]
*[[Renewable natural gas]]
*[[World energy resources and consumption]]
{{div col end}}

==References==
{{Reflist|30em}}

{{DEFAULTSORT:Natural Gas}}
[[Category:Natural gas| ]]
[[Category:Fuel gas]]

[[af:Aardgas]]
[[ar:غاز طبيعي]]
[[an:Gas natural]]
[[bn:প্রাকৃতিক গ্যাস]]
[[be:Прыродны газ]]
[[be-x-old:Прыродны газ]]
[[bs:Zemni plin]]
[[bg:Природен газ]]
[[ca:Gas natural]]
[[cs:Zemní plyn]]
[[cy:Nwy naturiol]]
[[da:Naturgas]]
[[de:Erdgas]]
[[et:Maagaas]]
[[el:Φυσικό αέριο]]
[[es:Gas natural]]
[[eo:Tergaso]]
[[eu:Gas natural]]
[[fa:گاز طبیعی]]
[[fr:Gaz naturel]]
[[fy:Ierdgas]]
[[ga:Gás nádúrtha]]
[[gl:Gas natural]]
[[ko:천연 가스]]
[[hi:प्राकृतिक गैस]]
[[hr:Prirodni plin]]
[[id:Gas alam]]
[[is:Jarðgas]]
[[it:Gas naturale]]
[[he:גז טבעי]]
[[jv:Gas bumi]]
[[ka:ბუნებრივი აირი]]
[[sw:Gesi asilia]]
[[ku:Erdgaz]]
[[lv:Dabasgāze]]
[[lt:Gamtinės dujos]]
[[lmo:Gass natüral]]
[[hu:Földgáz]]
[[mk:Земен гас]]
[[mr:नैसर्गिक वायू]]
[[ms:Gas asli]]
[[mn:Байгалийн хий]]
[[nl:Aardgas]]
[[nds-nl:Eerdgas]]
[[ja:天然ガス]]
[[no:Naturgass]]
[[nn:Naturgass]]
[[pl:Gaz ziemny]]
[[pt:Gás natural]]
[[ro:Gaz natural]]
[[qu:Allpa wapsi]]
[[ru:Природный газ]]
[[rue:Земный ґаз]]
[[sq:Gazi natyror]]
[[simple:Natural gas]]
[[sk:Zemný plyn]]
[[sl:Zemeljski plin]]
[[sr:Zemni gas]]
[[sh:Zemni gas]]
[[fi:Maakaasu]]
[[sv:Naturgas]]
[[ta:இயற்கை எரிவளி]]
[[te:సహజ వాయువు]]
[[th:แก๊สธรรมชาติ]]
[[tr:Doğal gaz]]
[[uk:Природний газ]]
[[vi:Khí thiên nhiên]]
[[zh-yue:天然氣]]
[[zh:天然气]]

Revision as of 16:26, 25 April 2012

HORSES!:)

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