Editing Natural gas (section)

==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 [[drilling rig]] in Texas, US]]
In the 19th century, natural gas was primarily obtained as a by-product of [[Oil well|producing oil]]. 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 soft drink bottle where the carbon dioxide [[effervesce]]s. The gas was often viewed as a by-product, a hazard, and a disposal problem in active oil fields. The large volumes produced could not be used until relatively expensive [[pipeline transport|pipeline]] and [[natural gas storage|storage]] facilities were constructed to deliver the gas to consumer markets.

Until the early part of the 20th century, most natural gas associated with oil was either simply released or [[Gas flare|burned off]] at oil fields. [[Gas venting]] and [[production flaring]] are still practised in modern times, but efforts are ongoing around the world to retire them, and to replace them with other commercially viable and useful alternatives.<ref>{{Cite web |title=Global Gas Flaring Reduction Partnership |url=https://sustainabledevelopment.un.org/partnership/?p=1532 |access-date=2019-12-29 |publisher=[[United Nations]]}}</ref><ref>{{Cite web |title=UN Climate Initiatives Platform - Zero Routine Flaring by 2030 |url=http://climateinitiativesplatform.org/index.php/Zero_Routine_Flaring_by_2030 |access-date=2019-12-29 |publisher=[[United Nations]]}}</ref>

In addition to transporting gas via pipelines for use in power generation, other end uses for natural gas include export as [[LNG|liquefied natural gas]] (LNG) or conversion of natural gas into other liquid products via [[gas to liquids]] (GTL) technologies. GTL technologies can convert natural gas into liquids products such as gasoline, diesel or jet fuel. A variety of GTL technologies have been developed, including [[Fischer–Tropsch]] (F–T), methanol to gasoline (MTG) and [[syngas to gasoline plus]] (STG+). F–T produces a synthetic crude that can be further refined into finished products, while MTG can produce synthetic gasoline from natural gas. STG+ can produce drop-in gasoline, diesel, jet fuel and aromatic chemicals directly from natural gas via a single-loop process.<ref name="STG+">{{Cite web |date=February 2013 |title=Introduction to STG+ Technology |url=http://www.primusge.com/press-room/white-papers/ |access-date=2013-03-05 |website=Primus Green Energy}}</ref> In 2011, [[Royal Dutch Shell|Royal Dutch Shell's]] {{convert|140000|oilbbl|m3|sp=us}} per day F–T plant went into operation in [[Qatar]].<ref>{{Cite web |date=2011-06-13 |title=First cargo of Pearl GTL products ship from Qatar |url=http://www.shell.com/media/news-and-media-releases/2011/first-cargo-pearl.html |access-date=2017-11-19 |website=Shell Global}}</ref>

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]]).<ref>{{Cite web |title=Extraction |url=http://www.naturalgas.org/naturalgas/extraction.asp |archive-url=https://web.archive.org/web/20130708145258/http://www.naturalgas.org/naturalgas/extraction.asp |archive-date=2013-07-08 |publisher=NaturalGas.org}}</ref> It sometimes contains a significant amount 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 |title=Natural gas overview |url=http://www.naturalgas.org/overview/background.asp |url-status=dead |archive-url=https://web.archive.org/web/20110101063224/http://naturalgas.org/overview/background.asp |archive-date=2011-01-01 |access-date=2011-02-06 |publisher=Naturalgas.org}}</ref>

Natural gas extracted from oil wells is called casinghead gas (whether or not truly produced up the annulus and through a casinghead outlet) or associated gas. The [[natural gas industry]] is extracting an increasing quantity of gas from challenging, [[Unconventional (oil & gas) reservoir|unconventional]] [[History of the petroleum industry in Canada (natural gas)#Unconventional gas|resource types]]: [[sour gas]], [[tight gas]], [[shale gas]], and [[coalbed methane]].

There is some disagreement on which country has the largest proven gas reserves. Sources that consider that Russia has by far the largest proven reserves include the US [[Central Intelligence Agency]] (47,600&nbsp;km<sup>3</sup>)<ref>{{Cite encyclopedia |title=Natural Gas – Proved Reserves |encyclopedia=The World Factbook |publisher=Central Intelligence Agency |url=https://www.cia.gov/library/publications/the-world-factbook/rankorder/2253rank.html |access-date=2013-12-01 |archive-url=https://web.archive.org/web/20170307234405/https://www.cia.gov/library/publications/the-world-factbook/rankorder/2253rank.html |archive-date=2017-03-07 |url-status=dead}}</ref> and [[Energy Information Administration]] (47,800&nbsp;km<sup>3</sup>),<ref>US Energy Information Administration, International statistics, accessed 1 December 2013.</ref><ref>{{Cite web |title=U.S. Crude Oil, Natural Gas, and Natural Gas Proved Reserves, Year-end 2017 |url=https://www.eia.gov/naturalgas/crudeoilreserves/ |access-date=2019-08-26 |website=www.eia.gov}}</ref> as well as the [[Organization of Petroleum Exporting Countries]] (48,700&nbsp;km<sup>3</sup>).<ref>{{Cite web |title=Table 3.2 – World Proven Natural Gas Reserves by Country |url=http://www.opec.org/library/Annual%20Statistical%20Bulletin/interactive/current/FileZ/XL/T32.HTM |url-status=dead |archive-url=https://web.archive.org/web/20180227183441/http://www.opec.org/library/Annual%20Statistical%20Bulletin/interactive/current/FileZ/XL/T32.HTM |archive-date=2018-02-27 |access-date=2013-12-01 |publisher=OPEC}}</ref> Contrarily, [[BP]] credits Russia with only 32,900&nbsp;km<sup>3</sup>,<ref>{{Cite web |title=BP Statistical Review of World Energy June 2013 |url=http://www.bp.com/content/dam/bp/pdf/statistical-review/statistical_review_of_world_energy_2013.pdf |archive-url=https://web.archive.org/web/20131204120328/http://www.bp.com/content/dam/bp/pdf/statistical-review/statistical_review_of_world_energy_2013.pdf |archive-date=2013-12-04 |website=BP}}</ref> which would place it in second, slightly behind Iran (33,100 to 33,800&nbsp;km<sup>3</sup>, depending on the source).
[[File:Countries by Natural Gas Proven Reserves (2014).svg|thumb|upright=2|Countries by [[List of countries by natural gas proven reserves|natural gas proven reserves]] (2014), based on data from The World Factbook]]

It is estimated that there are about 900,000&nbsp;km<sup>3</sup> of "unconventional" gas such as shale gas, of which 180,000&nbsp;km<sup>3</sup> may be recoverable.<ref>{{Cite web |last=Helen Knight |date=2010-06-12 |title=Wonderfuel: Welcome to the age of unconventional gas |url=https://www.newscientist.com/article/mg20627641.100-wonderfuel-welcome-to-the-age-of-unconventional-gas.html?full=true |url-access=subscription |website=[[New Scientist]] |pages=44–47}}</ref> In turn, many studies from [[MIT]], [[Black & Veatch]] and the [[US Department of Energy]] predict that natural gas will account for a larger portion of electricity generation and heat in the future.<ref>{{Cite web |last=Michael Kanellos |date=2011-06-09 |title=In Natural Gas, U.S. Will Move From Abundance to Imports |url=http://www.greentechmedia.com/articles/read/with-natural-gas-will-we-swap-oil-imports-for-gas-imports/ |website=Greentech Media}}</ref>{{Better source needed|reason=The current source is too old|date=October 2022}}

The world's largest gas field is the offshore [[South Pars/North Dome Gas-Condensate field]], shared between Iran and Qatar. It is estimated to have {{convert|51000|km3|mi3|sp=us}} of natural gas and {{convert|50|e9oilbbl|e9m3|abbr=off|sp=us}} of [[Natural-gas condensate|natural gas condensates]].

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 depleted. 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.

===Shale gas===
[[File:GasDepositDiagram.jpg|thumb|upright=2.0|The location of [[shale gas]] compared to other types of gas deposits]]
{{main|Shale gas}}

Shale gas is natural gas produced from [[shale]]. Because shale's matrix permeability is too low to allow gas to flow in economical quantities, shale gas wells depend on fractures to allow the gas to flow. Early shale gas wells depended on natural fractures through which gas flowed; almost all shale gas wells today require fractures artificially created by [[hydraulic fracturing]]. Since 2000, shale gas has become a major source of natural gas in the United States and Canada.<ref>{{Cite web |last=Mouawad |first=Jad |date=2009-06-17 |title=Estimate places natural gas reserves 35% higher |url=https://www.nytimes.com/2009/06/18/business/energy-environment/18gas.html |access-date=2009-10-25 |website=The New York Times}}</ref> Because of increased shale gas production the United States was in 2014 the number one natural gas producer in the world.<ref>{{Cite web |last=Morris Beschloss |date=2014-09-02 |title=U.S. Now World's Leading Natural Gas Producer |url=http://www.desertsun.com/story/money/industries/morrisbeschlosseconomics/2014/09/02/u-s-now-worlds-leading-natural-gas-producer/14976767/ |access-date=2014-11-04 |website=Desert Sun}}</ref> The production of shale gas in the United States has been described as a "shale gas revolution" and as "one of the landmark events in the 21st century."<ref>{{Cite journal |last1=Wang |first1=Qiang |last2=Chen |first2=Xi |last3=Jha |first3=Awadhesh N. |last4=Rogers |first4=Howard |date=February 2014 |title=Natural gas from shale formation – The evolution, evidences and challenges of shale gas revolution in United States |journal=Renewable and Sustainable Energy Reviews |volume=30 |pages=1–28 |doi=10.1016/j.rser.2013.08.065|bibcode=2014RSERv..30....1W }}</ref>

Following the increased production in the United States, shale gas exploration is beginning in countries such as Poland, China, and South Africa.<ref>{{Cite news |year=2012 |title=Poland Seeks to Boost Shale Gas Industry |work=Financial Times |url=http://www.ft.com/intl/cms/s/0/76c6ec14-17ad-11e2-9530-00144feabdc0.html#axzz29foGuSzc |url-status=live |url-access=subscription |access-date=2012-10-18 |archive-url=https://ghostarchive.org/archive/VA3Os |archive-date=2022-12-10}}</ref><ref>{{Cite web |last=Catherine T. Yang |date=2012-08-09 |title=China Drills into Shale Gas, Targeting Huge Reserves Amid Challenges |url=http://news.nationalgeographic.com/news/energy/2012/08/120808-china-shale-gas/ |archive-url=https://web.archive.org/web/20120810174014/http://news.nationalgeographic.com/news/energy/2012/08/120808-china-shale-gas/ |url-status=dead |archive-date=10 August 2012 |access-date=2012-10-18 |website=National Geographic}}</ref><ref>{{Cite news |last1=Franz Wild |last2=Andres R. Martinez |date=2012-09-07 |title=South Africa Allows Exploration of Shale Gas Resources |work=Bloomberg.com |url=https://www.bloomberg.com/news/2012-09-07/south-africa-allows-exploration-of-shale-gas-resources.html |url-access=subscription |access-date=2012-10-18}}</ref> Chinese geologists have identified the [[Sichuan Basin]] as a promising target for shale gas drilling, because of the similarity of shales to those that have proven productive in the United States. Production from the Wei-201 well is between 10,000 and 20,000 m<sup>3</sup> per day.<ref>{{Cite journal |last1=Zou |first1=Caineng |last2=Dong |first2=Dazhong |last3=Wang |first3=Shejiao |last4=Li |first4=Jianzhong |last5=Li |first5=Xinjing |last6=Wang |first6=Yuman |last7=Li |first7=Denghua |last8=Cheng |first8=Keming |date=December 2010 |title=Geological characteristics and resource potential of shale gas in China |journal=Petroleum Exploration and Development |volume=37 |issue=6 |pages=641–653 |doi=10.1016/S1876-3804(11)60001-3 |bibcode=2010PEDO...37..641Z |doi-access=free}}</ref> In late 2020, China National Petroleum Corporation claimed daily production of 20 million cubic meters of gas from its Changning-Weiyuan demonstration zone.<ref>{{Cite news |date=2020-10-13 |title=Shale gas production soars in SW China base |publisher=China Daily Information Co |agency=ChinaDaily.com.cn |url=https://www.chinadaily.com.cn/a/202010/13/WS5f852220a31024ad0ba7e5bd.html |access-date=2020-12-02}}</ref>{{Unreliable source?|date=November 2021}}

===Town gas===
{{Main|History of manufactured fuel gases}}

[[Town gas]] is a flammable gaseous fuel made by the destructive distillation of [[coal]]. It contains a variety of calorific gases including [[hydrogen]], [[carbon monoxide]], [[methane]], and other volatile [[hydrocarbon]]s, together with small quantities of non-calorific gases such as [[carbon dioxide]] and [[nitrogen]], and was used in a similar way to natural gas. This is a historical technology and is not usually economically competitive with other sources of fuel gas today.

Most town "gashouses" located in the eastern US in the late 19th and early 20th centuries were simple by-product [[coke (fuel)|coke]] ovens that 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 [[Bitumen|asphalt]]) that collected in the bottoms of the gashouse ovens was often used for roofing and other waterproofing purposes, and when mixed with sand and gravel was used for paving streets.

===Crystallized natural gas – clathrates===
Huge quantities of natural gas (primarily methane) exist in the form of [[methane clathrate|clathrates]] 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.

In 2013, Japan Oil, Gas and Metals National Corporation (JOGMEC) announced that they had recovered commercially relevant quantities of natural gas from methane hydrate.<ref>{{Cite web |last=Tabuchi |first=Hiroko |author-link=Hiroko Tabuchi |date=2013-03-12 |title=An Energy Coup for Japan: 'Flammable Ice' |url=https://www.nytimes.com/2013/03/13/business/global/japan-says-it-is-first-to-tap-methane-hydrate-deposit.html |website=The New York Times}}</ref>