Editing Natural gas (section)

===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.