From Wikipedia, the free encyclopediaNot to be confused with gasoline, biogas, or liquefied petroleum gas.Natural gas burning on a gas stoveBurning of natural gas coming out of the ground

Natural gas (also called fossil gas, methane gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon dioxide, nitrogen, hydrogen sulfide, and helium are also usually present.^[1] Methane is colorless and odorless, and the second largest greenhouse gas contributor to global climate change after carbon dioxide.^[2] Because natural gas is odorless, odorizers such as mercaptan (which smells like sulfur or rotten eggs) are commonly added to it for safety so that leaks can be readily detected.^[3]

Natural gas is a fossil fuel and non-renewable resource that is formed when layers of organic matter (primarily marine microorganisms)^[4] decompose under anaerobic conditions and are subjected to intense heat and pressure underground over millions of years.^[5] The energy that the decayed organisms originally obtained from the sun via photosynthesis is stored as chemical energy within the molecules of methane and other hydrocarbons.^[6]

天然气(也称为化石气、甲烷气或简称天然气)是一种天然存在的气态碳氢化合物混合物，主要由甲烷和各种少量的其他高级烷烃组成。低水平的微量气体，如二氧化碳、氮、硫化氢和氦通常也存在。[1]甲烷无色无味，是仅次于二氧化碳的导致全球气候变化的第二大温室气体。[2]由于天然气是无味的，为了安全起见，通常会在天然气中添加硫醇(闻起来像硫磺或臭鸡蛋)等增味剂，这样就可以很容易地检测到泄漏。[3]天然气是一种化石燃料和不可再生资源，是有机物层(主要是海洋微生物)[4]在厌氧条件下分解并在地下承受数百万年的高温和高压而形成的[5]。腐烂的生物体最初通过光合作用从太阳获得的能量以化学能的形式储存在甲烷和其他碳氢化合物的分子中。[6]

Natural gas can be burned for heating, cooking,^[7] and electricity generation. It is also used as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals and less commonly used as a fuel for vehicles.

The extraction and consumption of natural gas is a major and growing contributor to climate change.^[8][9][10] Both the gas itself (specifically methane) and carbon dioxide, which is released when natural gas is burned, are greenhouse gases.^[11][12] When burned for heat or electricity, natural gas emits fewer toxic air pollutants, less carbon dioxide, and almost no particulate matter compared to other fossil and biomass fuels.^[13] However, gas venting and unintended fugitive emissions throughout the supply chain can result in natural gas having a similar carbon footprint to other fossil fuels overall.^[14]

Natural gas can be found in underground geological formations, often alongside other fossil fuels like coal and oil (petroleum). Most natural gas has been created through either biogenic or thermogenic processes. Biogenic gas is formed when methanogenic organisms in marshes, bogs, landfills, and shallow sediments anaerobically decompose but are not subjected to high temperatures and pressures. Thermogenic gas takes a much longer period of time to form and is created when organic matter is heated and compressed deep underground.^[15][5]

During petroleum production, natural gas is sometimes flared rather than being collected and used. Before natural gas can be burned as a fuel or used in manufacturing processes, it almost always has to be processed to remove impurities such as water. The byproducts of this processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons. Hydrogen sulfide (which may be converted into pure sulfur), carbon dioxide, water vapor, and sometimes helium and nitrogen must also be removed.

Natural gas is sometimes informally referred to simply as "gas", especially when it is being compared to other energy sources, such as oil, coal or renewables. However, it is not to be confused with gasoline, which is often shortened in colloquial usage to "gas", especially in North America.^[16]

Natural gas is measured in standard cubic meters or standard cubic feet. The density compared to air ranges from 0.58 (16.8 g/mole, 0.71 kg per standard cubic meter) to as high as 0.79 (22.9 g/mole, 0.97 kg per scm), but generally less than 0.64 (18.5 g/mole, 0.78 kg per scm).^[17] For comparison, pure methane (16.0425 g/mole) has a density 0.5539 times that of air (0.678 kg per standard cubic meter).

   天然气可以用于加热、烹饪[7]和发电。它也被用作制造塑料和其他商业上重要的有机化学品的化学原料，不太常用作汽车燃料。天然气的开采和消耗是造成气候变化的一个主要因素，而且越来越重要。[8][9][10]天然气本身(特别是甲烷)和天然气燃烧时释放的二氧化碳都是温室气体。[11][12]与其他化石燃料和生物质燃料相比，天然气燃烧取暖或发电时排放的有毒空气污染物和二氧化碳更少，而且几乎没有颗粒物质。[13]然而，整个供应链中的气体排放和无意的逃逸排放可能导致天然气的碳足迹与其他化石燃料相似。[14]天然气可以在地下地质构造中找到，通常与煤和石油等其他化石燃料一起发现。大多数天然气都是通过生物或热生过程产生的。生物气是由沼泽、沼泽、垃圾填埋场和浅层沉积物中的产甲烷生物厌氧分解形成的，但不受高温和高压的影响。产热气体的形成需要更长的时间，当有机物在地下深处被加热和压缩时就会产生。[15][5]在石油生产过程中，天然气有时是燃烧而不是收集和使用。在天然气作为燃料燃烧或用于制造过程之前，它几乎总是必须经过处理以去除水等杂质。这一过程的副产物包括乙烷、丙烷、丁烷、戊烷和更高分子量的碳氢化合物。硫化氢(可以转化为纯硫)、二氧化碳、水蒸气，有时还必须除去氦和氮。天然气有时被非正式地简称为“天然气”，特别是当它与其他能源(如石油、煤炭或可再生能源)相比时。然而，不要将它与汽油混淆，后者在口语中经常被简称为“gas”，尤其是在北美。[16]天然气的计量单位是标准立方米或标准立方英尺。与空气相比，密度从0.58 (16.8 g/mol, 0.71 kg /标准立方米)到0.79 (22.9 g/mol, 0.97 kg / scm)，但通常小于0.64 (18.5 g/mol, 0.78 kg / scm)。[17]相比之下，纯甲烷(16.0425 g/mol)的密度是空气(0.678 kg /标准立方米)的0.5539倍。

Name[edit]

In the early 1800s, natural gas became known as "natural" to distinguish it from the dominant gas fuel at the time, coal gas.^[18] Unlike coal gas, which is manufactured by heating coal, natural gas can be extracted from the ground in its native gaseous form. When the use of natural gas overtook the use of coal gas in English speaking countries in the 20th century, it was increasingly referred to as simply "gas."^[19] In order to highlight its role in exacerbating the climate crisis, however, many organizations have criticized the continued use of the word "natural" in referring to the gas. These advocates prefer the term "fossil gas" or "methane gas" as better conveying to the public its climate threat.^[20][21][22] A 2020 study of Americans' perceptions of the fuel found that, across political identifications, the term "methane gas" led to better estimates of its harms and risks.^[23]

19世纪初，天然气被称为“天然”，以区别于当时占主导地位的天然气燃料——煤气。[18]与通过加热煤炭生产的煤气不同，天然气可以以天然的气态形式从地下开采出来。20世纪，当英语国家对天然气的使用超过了对煤气的使用时，人们越来越多地将天然气简称为“gas”。[19]然而，为了强调它在加剧气候危机中的作用，许多组织批评继续使用“天然”一词来指代天然气。这些倡导者更喜欢用“化石气体”或“甲烷气体”来更好地向公众传达气候威胁。[20][21][22] 2020年一项关于美国人对这种燃料看法的研究发现，无论政治立场如何，“甲烷气”一词都能让人们更好地估计其危害和风险。[23]

History[edit]

A gas bill from Baltimore, Maryland, 1834, for manufactured coal gas, before the introduction of ground-extracted methane gas.

Natural gas can come out of the ground and cause a long-burning fire. In ancient Greece, the gas flames at Mount Chimaera contributed to the legend of the fire-breathing creature Chimera. In ancient China, gas resulting from the drilling for brines was first used by about 400 BC.^[24] The Chinese transported gas seeping from the ground in crude pipelines of bamboo to where it was used to boil salt water to extract the salt in the Ziliujing District of Sichuan.^[25][26]

Natural gas was not widely used before the development of long distance pipelines in the early twentieth century. Before that, most use was near to the source of the well, and the predominant gas for fuel and lighting during the industrial revolution was manufactured coal gas.^[27]

The history of natural gas in the United States begins with localized use. In the seventeenth century, French missionaries witnessed the American Indians setting fire to natural gas seeps around lake Erie, and scattered observations of these seeps were made by European-descended settlers throughout the eastern seaboard through the 1700s.^[28] In 1821, William Hart dug the first commercial natural gas well in the United States at Fredonia, New York, United States, which led in 1858 to the formation of the Fredonia Gas Light Company.^[29] Further such ventures followed near wells in other states, until technological innovations allowed the growth of major long distance pipelines from the 1920s onward.^[28]By 2009, 66,000 km³ (16,000 cu mi) (or 8%) had been used out of the total 850,000 km³ (200,000 cu mi) of estimated remaining recoverable reserves of natural gas.^[30]

1834年，马里兰州巴尔的摩市的煤气费账单，当时还没有引入地面提取的甲烷气体。天然气会从地下冒出来，引起长时间燃烧的大火。在古希腊，奇美拉山的气体火焰促成了喷火生物奇美拉的传说。在古代中国，大约在公元前400年，人们首次使用钻探盐水产生的天然气。[24]中国人用粗制的竹子管道将地下渗出的天然气输送到四川自流井地区，在那里用竹子煮沸盐水提取盐。[25][26]在20世纪初长距离管道发展之前，天然气没有得到广泛使用。在此之前，大部分使用都是在靠近井源的地方，在工业革命期间，主要用于燃料和照明的气体是人造煤气。[27]美国天然气的历史始于局部使用。17世纪，法国传教士目睹了美洲印第安人在伊利湖周围的天然气渗漏处放火，18世纪整个东部沿海地区的欧洲后裔定居者对这些渗漏处进行了零星的观察。[28]1821年，威廉·哈特在美国纽约州弗雷多尼亚挖出了美国第一口商业天然气井，这导致了1858年弗雷多尼亚煤气灯公司的成立。[29]其他州的油井附近也出现了类似的企业，直到20世纪20年代以来，技术创新允许主要长距离管道的发展。[28]到2009年，估计剩余天然气可采储量为850,000 km3 (200,000 cu mi)，其中66,000 km3 (16,000 cu mi)(或8%)已被使用

Sources[edit]

See also: List of natural gas fields, List of countries by natural gas proven reserves, and List of countries by natural gas production

Natural gas[edit]

Natural gas drilling rig in Texas, US

In the 19th century, natural gas was primarily obtained as a by-product of producing oil. The small, light gas carbon chains came out of solution as the extracted fluids underwent pressure reduction from the reservoir to the surface, similar to uncapping a soft drink bottle where the carbon dioxide effervesces. 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 and 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 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.^[31][32] Unwanted gas (or stranded gas without a market) is often returned to the reservoir with 'injection' wells while awaiting a possible future market or to re-pressurize the formation, which can enhance oil extraction rates from other wells. In regions with a high natural gas demand (such as the US), pipelines are constructed when it is economically feasible to transport gas from a wellsite to an end consumer.

In addition to transporting gas via pipelines for use in power generation, other end uses for natural gas include export as 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.^[33] In 2011, Royal Dutch Shell's 140,000 barrels (22,000 m³) per day F–T plant went into operation in Qatar.^[34]

Natural gas can be "associated" (found in oil fields), or "non-associated" (isolated in natural gas fields), and is also found in coal beds (as coalbed methane).^[35] 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.^[36]

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 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 km³)^[37] and Energy Information Administration (47,800 km³),^[38][39] as well as the Organization of Petroleum Exporting Countries (48,700 km³).^[40] Contrarily, BP credits Russia with only 32,900 km³,^[41] which would place it in second, slightly behind Iran (33,100 to 33,800 km³, depending on the source).

在19世纪，天然气主要是通过生产石油的副产品而获得的。小而轻的天然气碳链在从储层到地表的压力降低过程中脱溶出来，类似于打开汽水瓶时二氧化碳冒泡的现象。这种气体通常被视为副产品、危险因素和在活跃的油田中处理的问题。在相对昂贵的管道和储气设施建成以将气体输送到消费者市场之前，生产的大量气体无法使用。

直到20世纪初期，大多数与石油相关的天然气要么被简单地释放，要么在油田中被燃烧掉。通气和生产明火在现代仍然有所实践，但全球范围内正在努力淘汰它们，并用其他商业可行和有用的替代方法替代它们。不需要的天然气（或没有市场的滞留天然气）通常会通过“注入”井被返回到储层中，以等待可能的未来市场或重新增压形成，从而可以提高其他井的油提取率。在需求天然气高的地区（如美国），当从井场运送天然气到最终用户在经济上可行时，会修建管道。

除了通过管道运输天然气用于发电之外，天然气的其他用途包括出口为液化天然气（LNG）或通过气体到液体（GTL）技术将天然气转化为其他液体产品。GTL技术可以将天然气转化为汽油、柴油或喷气燃料等液体产品。已经开发了各种GTL技术，包括费舍尔-特普什（F–T）、甲醇制汽油（MTG）和合成气制汽油加（STG+）。F–T生产合成原油，可以进一步精炼成成品，而MTG可以从天然气中生产合成汽油。STG+可以通过单循环过程直接从天然气中生产滴定汽油、柴油、喷气燃料和芳香烃化学品。2011年，荷兰皇家壳牌公司在卡塔尔投产了每天14万桶（22,000立方米）的F–T工厂。

天然气可以是“伴生的”（在油田中发现），也可以是“非伴生的”（孤立在天然气田中），还可以在煤层中发现（作为煤层气）。它有时包含大量的乙烷、丙烷、丁烷和戊烷——这些较重的烃类在将甲烷作为消费者燃料或化工厂原料出售之前会被去除。天然气还必须去除非烃类，如二氧化碳、氮气、氦气（很少）、硫化氢，然后才能进行输送。

从油井提取的天然气被称为套管头气（无论是否真正通过环空和套管头出口产出），或称为伴生气。天然气行业正在从具有挑战性的非常规资源类型中提取越来越多的气体，包括酸性气体、致密气体、页岩气和煤层气。

关于哪个国家拥有最大的已探明天然气储量存在一些分歧。认为俄罗斯拥有远远最大的已探明储量的来源包括美国中央情报局（47,600 km3）、能源信息管理局（47,800 km3）以及石油输出国组织（48,700 km3）。相反，英国石油公司（BP）只认为俄罗斯有32,900 km3，这将使其位于第二位，略微落后于伊朗（根据不同来源，伊朗的储量为33,100到33,800 km3不等）。

Countries by natural gas proven reserves (2014), based on data from The World Factbook

It is estimated that there are about 900,000 km³ of "unconventional" gas such as shale gas, of which 180,000 km³ may be recoverable.^[42] 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.^{[43][better source needed]}

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 51,000 cubic kilometers (12,000 cu mi) of natural gas and 50 billion barrels (7.9 billion cubic meters) of 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 (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 gas plant is to collect this condensate. The resulting liquid is called natural gas liquid (NGL) and has commercial value.

按照2014年的数据来看，各国的天然气已探明储量如下：

据估计，约有900,000立方千米的“非常规”天然气储量，如页岩气，其中可能有180,000立方千米可以被开采。与此同时，来自麻省理工学院、布莱克和维奇以及美国能源部的许多研究预测，未来天然气将占据更大比例的电力生成和供热领域。

世界上最大的天然气田是位于伊朗和卡塔尔之间的离岸南帕斯/北圆顶气-凝析气田。据估计，它拥有51,000立方千米的天然气和50亿桶（7.9亿立方米）的天然气凝析油。

由于天然气不是一种纯产品，当从非伴生气体田采出超临界（压力/温度）条件下的气体时，随着储层压力的降低，较高分子量的组分可能会部分冷凝成等温减压时所称的逆向冷凝效应。因此形成的液体可能会被困在气体储层的孔隙中，导致储层逐渐枯竭。解决这个问题的一种方法是重新注入不含凝析物的干燥天然气，以维持地下压力，并允许凝析物重新蒸发和提取。更常见的情况是液体在地表冷凝，而天然气厂的任务之一就是收集这种凝析物。由此产生的液体称为天然气液体（NGL），具有商业价值。

Shale gas[edit]

The location of shale gas compared to other types of gas depositsMain article: Shale gas

Shale gas is natural gas produced from shale. Because shale has matrix permeability 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.^[44] Because of increased shale gas production the United States was in 2014 the number one natural gas producer in the world.^[45] 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."^[46]

Following the increased production in the United States, shale gas exploration is beginning in countries such as Poland, China, and South Africa.^[47][48][49] 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 m³ per day.^[50] In late 2020, China National Petroleum Corporation claimed daily production of 20 million cubic meters of gas from its Changning-Weiyuan demonstration zone.^{[51][unreliable source?]}

页岩气是从页岩中产出的天然气。由于页岩的基质渗透性太低，无法以经济数量的天然气流动，因此页岩气井依赖于裂缝来允许天然气流动。早期的页岩气井依赖于自然裂缝，通过这些裂缝气体流动；而几乎所有现代的页岩气井都需要通过水力压裂来人工创建裂缝，以允许气体流动。自2000年以来，页岩气已成为美国和加拿大的主要天然气来源[44]。由于页岩气产量的增加，2014年美国成为世界上第一大天然气生产国[45]。美国的页岩气产量被描述为“页岩气革命”和“21世纪的重大事件之一”[46]。

在美国产量增加之后，波兰、中国和南非等国家开始进行页岩气勘探[47][48][49]。中国的地质学家已确定四川盆地是页岩气钻探的有希望的目标，因为该地的页岩与在美国已经被证明具有生产潜力的页岩相似。来自Wei-201井的产量在每天10,000至20,000立方米之间[50]。2020年底，中国石油天然气集团公司声称其长宁-威远示范区每天生产2000万立方米的天然气[51][不可靠的消息来源？

^{Town gas}

Main article: 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 hydrocarbons, 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 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 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[edit]

Huge quantities of natural gas (primarily methane) exist in the form of 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.^[52]

主要文章：制造燃气的历史 城市煤气是一种由煤炭的破坏性干馏制备的易燃气体燃料。它包含各种热值气体，包括氢气、一氧化碳、甲烷和其他挥发性碳氢化合物，还含有少量非热值气体，如二氧化碳和氮气，用法类似于天然气。这是一项历史性技术，通常在今天与其他燃气来源不具备经济竞争力。

19世纪末和20世纪初，位于美国东部的大多数城市“煤气厂”都是简单的副产品焦炉，它们在密封的炉室中加热沥青煤。从煤炭中挥发出来的煤气被收集并通过管道网络分配到住宅和其他建筑物，用于烹饪和照明（直到20世纪下半叶，燃气供暖并不普及）。在煤气厂炉底收集的焦油（或沥青）通常用于屋顶和其他防水用途，与沙子和砾石混合后用于铺设街道。

结晶天然气 - 珍冰 大量的天然气（主要是甲烷）以珍冰的形式存在于沉积物下的海上大陆架和北极地区的陆地，那里有永久冻土，比如西伯利亚等地。珍冰需要高压和低温的结合才能形成。

2013年，日本石油、天然气和金属国家公司（JOGMEC）宣布，他们从甲烷珍冰中恢复了商业上相关数量的天然气[52]。

Processing[edit]

Main article: Natural gas processingNatural gas processing plant in Aderklaa, Lower Austria

The image below is a schematic 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 +).^{[53][54][55][56]}

Schematic flow diagram of a typical natural gas processing plant

Demand[edit]

See also: Gas depletionNatural gas extraction by countries in cubic meters per year around 2013

The examples and perspective in this section deal primarily with US and do not represent a worldwide view of the subject. You may improve this section, discuss the issue on the talk page, or create a new section, as appropriate. (October 2022) (Learn how and when to remove this template message)

As of mid-2020, natural gas production in the US had peaked three times, with current levels exceeding both previous peaks. It reached 24.1 trillion cubic feet per year in 1973, followed by a decline, and reached 24.5 trillion cubic feet in 2001. After a brief drop, withdrawals increased nearly every year since 2006 (owing to the shale gas boom), with 2017 production at 33.4 trillion cubic feet and 2019 production at 40.7 trillion cubic feet. After the third peak in December 2019, extraction continued to fall from March onward due to decreased demand caused by the COVID-19 pandemic in the US.^[57]

The 2021 global energy crisis was driven by a global surge in demand as the world quit the economic recession caused by COVID-19, particularly due to strong energy demand in Asia.^[58]

Storage and transport[edit]

See also: List of natural gas pipelinesPolyethylene plastic main being placed in a trenchConstruction close to high pressure gas transmission pipelines is discouraged, often with standing warning signs.^[59]

This section needs to be updated. The reason given is: change in transport from Russia. Please help update this article to reflect recent events or newly available information. (May 2022)

Because of its low density, it is not easy to store natural gas or to transport it by vehicle. Natural gas pipelines are impractical across oceans, since the gas needs to be cooled down and compressed, as the friction in the pipeline causes the gas to heat up. Many existing pipelines in the US are close to reaching their capacity, prompting some politicians representing northern states to speak of potential shortages. The large trade cost implies that natural gas markets are globally much less integrated, causing significant price differences across countries. In Western Europe, the gas pipeline network is already dense.^{[60][better source needed][full citation needed]} New pipelines are planned or under construction between Western Europe and the Near East or Northern Africa.^[61]

Whenever gas is bought or sold at custody transfer points, rules and agreements are made regarding the gas quality. These may include the maximum allowable concentration of CO
2, H
2S and H
2O. Usually sales quality gas that has been treated to remove contamination is traded on a "dry gas" basis and is required to be commercially free from objectionable odours, materials, and dust or other solid or liquid matter, waxes, gums and gum forming constituents, which might damage or adversely affect operation of equipment downstream of the custody transfer point.

LNG carrier ships transport liquefied natural gas (LNG) across oceans, while tank trucks can carry LNG or compressed natural gas (CNG) over shorter distances.^[62] Sea transport using CNG carrier ships that are now under development may be competitive with LNG transport in specific conditions.^{[citation needed]}

Gas is turned into liquid at a liquefaction plant, and is returned to gas form at regasification plant at the 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 km (2,500 mi) over land and approximately half that distance offshore.

CNG is transported at high pressure, typically above 200 bars (20,000 kPa; 2,900 psi). 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.

由于其密度低，不容易储存天然气或用车辆运输。跨越海洋的天然气管道是不切实际的，因为天然气需要冷却和压缩，因为管道中的摩擦会导致天然气升温。美国许多现有的管道已接近达到其容量，这促使一些代表北方各州的政界人士谈到了潜在的短缺。巨大的贸易成本意味着全球天然气市场的整合程度要低得多，导致各国之间的价格差异很大。在西欧，天然气管道网络已经很密集。[60][需要更好的来源][需要完整的引用]西欧和近东或北非之间的新管道正在计划或正在建设中。[61]每当天然气在托管转移点买卖时，就会制定有关天然气质量的规则和协议。这些可能包括co2、h2s和h2o的最大允许浓度。通常，经过处理以去除污染的销售优质气体以“干气”为基础进行交易，并要求商业上不含令人反感的气味、物质、灰尘或其他固体或液体物质、蜡、树胶和树胶形成成分，这些物质可能会损坏或对保管转移点下游设备的操作产生不利影响。LNG运输船跨洋运输液化天然气(LNG)，而油罐车可以在较短的距离上运输LNG或压缩天然气(CNG)。[62]目前正在开发的使用CNG运输船的海上运输在特定条件下可能与液化天然气运输具有竞争力。[引证需要]气体在液化厂转化为液体，并在终端的再气化厂返回为气体形式。还使用船载再气化设备。液化天然气是长距离、大批量天然气运输的首选形式，而管道运输则是陆地上长达4,000公里(2,500英里)的运输方式，海上运输距离约为管道运输距离的一半。CNG在高压下运输，通常在200巴(20,000 kPa)以上;2900 psi)。与液化/再气化装置相比，压缩机和减压设备的资本密集程度较低，在较小的装置尺寸下可能更经济。天然气卡车和运输船可以将天然气直接运输到最终用户，或者运输到分销点，如管道。

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 flaring. Flaring is now illegal in many countries.^[63] Additionally, higher demand in the last 20–30 years has made production of gas associated with oil economically viable. As a further option, the gas is now sometimes re-injected into the formation for enhanced oil recovery by pressure maintenance as well as miscible or immiscible flooding. Conservation, re-injection, or flaring of natural gas associated with oil is primarily dependent on proximity to markets (pipelines), and regulatory restrictions.

Natural gas can be indirectly exported through the absorption in other physical output. A recent study suggests that the expansion of shale gas production in the US has caused prices to drop relative to other countries. This has caused a boom in energy intensive manufacturing sector exports, whereby the average dollar unit of US manufacturing exports has almost tripled its energy content between 1996 and 2012.^[64]

A "master gas system" was invented in Saudi Arabia in the late 1970s, ending any necessity for flaring. Satellite and nearby infra-red camera observations, however, shows that flaring^{[65][66][67][68]} and venting^[69] are still happening in some 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 [references about geological storage needed]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.^[70] 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.^[71] The United States is preparing to export natural gas.^[72]

美国伊利诺斯州尚佩恩县Newcomb镇的Manlove气田天然气储存区。前景(左)是地下储存区的众多井之一，其中有一个液化天然气工厂，背景(右)是地上储罐。在过去，在石油回收过程中回收的天然气不能出售获利，而只是在油田燃烧，这一过程被称为燃烧。现在，在许多国家，燃除天然气是非法的。[63]此外，过去20-30年的高需求使得与石油相关的天然气生产在经济上可行。作为进一步的选择，现在有时将气体重新注入地层，通过维持压力以及混相或非混相驱来提高采收率。与石油相关的天然气的保护、回注或燃烧主要取决于是否靠近市场(管道)和监管限制。天然气可以通过其他实物产出的吸收间接出口。最近的一项研究表明，美国页岩气产量的扩大导致价格相对于其他国家有所下降。这导致了能源密集型制造业出口的繁荣，美国制造业出口的平均美元单位在1996年至2012年间几乎增加了两倍的能源含量。[64]20世纪70年代末，沙特阿拉伯发明了一种“主天然气系统”，结束了任何燃除的必要性。然而，卫星和附近的红外相机观测显示，在一些国家，燃烧[65][66][67][68]和喷吐[69]仍在发生。天然气被用来为海水淡化发电和供热。同样，一些也排放甲烷气体的垃圾填埋场已经建立起来，以捕获甲烷并发电。天然气通常储存在地下[关于需要的地质储存的参考资料]，储存在以前的气井、盐丘开采的枯竭气藏中，或作为液化天然气储存在储罐中。天然气在需求低的时候注入，在需求上升的时候提取。终端用户附近的存储有助于满足不稳定的需求，但这种存储可能并不总是可行的。15个国家占全球天然气开采量的84%，获得天然气已成为国际政治中的一个重要问题，各国争夺对管道的控制权。[70]在21世纪的第一个十年，俄罗斯国有能源公司俄罗斯天然气工业股份公司(Gazprom)与乌克兰和白俄罗斯在天然气价格上发生了纠纷，这让人们担心，由于政治原因，向欧洲部分地区输送的天然气可能会被切断。[71]美国正准备出口天然气。[72]

Floating liquefied natural gas[edit]

Floating liquefied natural gas (FLNG) is an innovative technology designed to enable the development of offshore gas resources that would otherwise remain untapped due to environmental or economic factors which currently make them impractical to develop 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.^[73] 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.^[74]

Many gas and oil companies are considering the economic and environmental benefits of floating liquefied natural gas (FLNG). There are currently projects underway to construct five FLNG facilities. Petronas is close to completion on their FLNG-1^[75] at Daewoo Shipbuilding and Marine Engineering and are underway on their FLNG-2 project^[76] at Samsung Heavy Industries. Shell Prelude is due to start production 2017.^[77] The Browse LNG project will commence FEED in 2019.^[78]

浮式液化天然气(FLNG)是一项创新技术，旨在开发海上天然气资源，否则由于环境或经济因素，这些资源目前无法通过陆上液化天然气作业进行开发。FLNG技术还提供了许多环境和经济优势:环境-因为所有的处理都在气田完成，不需要长管道到岸上，不需要压缩装置将天然气泵到岸上，不需要疏浚和码头建设，也不需要在岸上建造液化天然气加工厂，这大大减少了环境足迹。[73]避免施工也有助于保护海洋和沿海环境。此外，在退役期间，环境干扰将最小化，因为在翻新和重新部署之前，设施可以很容易地断开连接并移除。经济-在将天然气输送到岸上的成本过高的情况下，FLNG使开发在经济上可行。因此，它将为开发近海天然气田的国家开辟新的商业机会，否则这些气田将继续搁浅，例如东非近海气田。[74]许多天然气和石油公司都在考虑浮式液化天然气(FLNG)的经济和环境效益。目前正在进行建设五个FLNG设施的项目。马来西亚国家石油公司(Petronas)在大宇造船海洋的FLNG-1项目(75)即将完工，在三星重工业的FLNG-2项目(76)也正在进行中。壳牌Prelude计划于2017年投产。[77]Browse液化天然气项目将于2019年启动FEED。[78]

Uses[edit]

Natural gas is primarily used in the northern hemisphere. North America and Europe are major consumers.

Often well head gases require removal of various hydrocarbon molecules contained within the gas. Some of these gases include heptane, pentane, propane and other hydrocarbons with molecular weights above methane (CH
4). The natural gas transmission lines extend to the natural gas processing plant or unit which removes the higher-molecular weight hydrocarbons to produce natural gas with energy content between 35–39 megajoules per cubic metre (950–1,050 British thermal units per cubic foot). The processed natural gas may then be used for residential, commercial and industrial uses.

Mid-stream natural gas[edit]

Natural gas flowing in the distribution lines is called mid-stream natural gas and is often used to power engines which rotate compressors. These compressors are required in the transmission line to pressurize and repressurize the mid-stream natural gas as the gas travels. Typically, natural gas powered engines require 35–39 MJ/m³ (950–1,050 BTU/cu ft) natural gas to operate at the rotational name plate specifications.^[79] Several methods are used to remove these higher molecular weighted gases for use by the natural gas engine. A few technologies are as follows:

天然气主要在北半球使用。北美和欧洲是主要的消费者。井口气体通常需要去除气体中含有的各种碳氢化合物分子。其中一些气体包括庚烷、戊烷、丙烷和其他分子量高于甲烷(ch4)的碳氢化合物。天然气输油管延伸到天然气加工厂或装置，这些工厂或装置可以去除较高分子量的碳氢化合物，生产能量含量在35-39兆焦耳/立方米(950 - 1050英热单位/立方英尺)之间的天然气。经过处理的天然气可用于住宅、商业和工业用途。中游天然气在输电线中流动的天然气被称为中游天然气，通常用来为带动压缩机的发动机提供动力。这些压缩机需要在输电线中对中游天然气进行加压和再加压。通常，天然气动力发动机需要35-39 MJ/m3 (950-1,050 BTU/立方英尺)的天然气来运行旋转铭牌规格。[79]有几种方法用于去除这些高分子量气体，供天然气发动机使用。以下是一些技术:

• Joule–Thomson skid

• Cryogenic or chiller system

• Chemical enzymology system^[79]

Power generation[edit]

This section is an excerpt from Gas-fired power plant.[edit]A cogeneration plant in BerlinShare of electricity production from gasA gas-fired power plant, sometimes referred to as gas-fired power station or natural gas power plant, is a thermal power station that burns natural gas to generate electricity. Gas-fired power plants generate almost a quarter of world electricity and are significant sources of greenhouse gas emissions.^[80] However, they can provide seasonal, dispatchable energy generation to compensate for variable renewable energy deficits, where hydropower or interconnectors are not available.

Domestic use[edit]

Manhole for domestic gas supply, London, UK

In the USA, over one-third of households (>40 million homes) cook with gas.^[2] Natural gas dispensed in a residential setting can generate temperatures in excess of 1,100 °C (2,000 °F) making it a powerful domestic cooking and heating fuel.^[81] Stanford scientists estimated that gas stoves emit 0.8–1.3% of the gas they use as unburned methane and that total U.S. stove emissions are 28.1 gigagrams of methane.^[2] In much of the developed world it is supplied through pipes to homes, where it is used for many purposes including ranges and ovens, heating/cooling, outdoor and portable grills, and central heating.^[82] Heaters in homes and other buildings may include boilers, furnaces, and water heaters. Both North America and Europe are major consumers of natural gas.

Domestic appliances, furnaces, and boilers use low pressure, usually with a standard preassure around 1.7 kilopascals (0.25 psi) over atmospheric preassure. The pressures in the supply lines vary, either the standard utilization pressure (UP) mentioned above or elevated pressure (EP), which may be anywhere from 7 to 800 kilopascals (1 to 120 psi) over atmospheric preassure. Systems using EP have a regulator at the service entrance to step down to UP.^[83]

Natural Gas Piping Systems inside buildings are often designed with pressures of 14 to 34 kilopascals (2 to 5 psi), and have downstream pressure regulators to reduce pressure as needed. In the United States the maximum allowable operating pressure for natural gas piping systems within a building is based on NFPA 54: National Fuel Gas Code,^[84] except when approved by the Public Safety Authority or when insurance companies have more stringent requirements.

Generally, natural gas system pressures are not allowed to exceed 5 psi (34 kPa) unless all of the following conditions are met:

• The AHJ will allow a higher pressure.

• The distribution pipe is welded. (Note: 2. Some jurisdictions may also require that welded joints be radiographed to verify continuity).

• The pipes are closed for protection and placed in a ventilated area that does not allow gas accumulation.

• The pipe is installed in the areas used for industrial processes, research, storage or mechanical equipment rooms.

Generally, a maximum liquefied petroleum gas pressure of 20 psi (140 kPa) is allowed, provided the building is used specifically for industrial or research purposes and is constructed in accordance with NFPA 58: Liquefied Petroleum Gas Code, Chapter 7.^[85]

A seismic earthquake valve operating at a pressure of 55 psig (3.7 bar) can stop the flow of natural gas into the site wide natural gas distribution piping network (that runs (outdoors underground, above building roofs, and or within the upper supports of a canopy roof). Seismic earthquake valves are designed for use at a maximum of 60 psig.^[86][87]

In Australia, natural gas is transported from gas processing facilities to regulator stations via Transmission pipelines. Gas is then regulated down to distributed pressures and the gas is distributed around a gas network via gas mains. Small branches from the network, called services, connect individual domestic dwellings, or multi-dwelling buildings to the network. The networks typically range in pressures from 7 kPa (low pressure) to 515 kPa (high pressure). Gas is then regulated down to 1.1 kPa or 2.75 kPa, before being metered and passed to the consumer for domestic use.^[88] Natural gas mains are made from a variety of materials: historically cast iron, though more modern mains are made from steel or polyethylene.

In some states in the USA natural gas can be supplied by independent natural gas wholesalers/suppliers using existing pipeline owners' infrastructure through Natural Gas Choice programs.

LPG (liquefied petroleum gas) typically fuels outdoor and portable grills. Although, compressed natural gas (CNG) is sparsely available for similar applications in the USA in rural areas underserved by the existing pipeline system and distribution network of the less expensive and more abundant LPG (liquefied petroleum gas).

在美国，超过三分之一的家庭（超过4000万户）使用天然气进行烹饪[2]。在家庭环境中使用的天然气可以产生超过1100摄氏度（2000华氏度）的温度，使其成为一种强大的家用烹饪和供暖燃料[81]。斯坦福科学家估计，燃气灶释放出0.8-1.3%的未燃烧甲烷，美国总的灶具排放量为28.1千克/千克甲烷[2]。在发达国家的大部分地区，天然气通过管道供应到住宅，用途广泛，包括灶具和烤箱、供暖/冷却、户外和便携式烧烤以及中央供暖[82]。家庭和其他建筑物中的加热器可能包括锅炉、炉子和热水器。北美和欧洲都是天然气的主要消费国。

家用电器、炉子和锅炉通常使用低压，通常标准压力为大气压以上1.7千帕斯卡（0.25 psi）。供应管道中的压力各不相同，可以是上述标准利用压力（UP）或升高的压力（EP），EP可以从大气压以上7到800千帕斯卡（1到120 psi）不等。使用EP的系统在服务入口处有一个调压器，以降低到UP[83]。

建筑物内的天然气管道系统通常设计为14至34千帕斯卡（2至5 psi）的压力，并具有下游的压力调节器，根据需要降低压力。在美国，建筑物内的天然气管道系统的最大允许操作压力是基于NFPA 54：国家燃气代码[84]，除非得到公共安全当局批准或保险公司有更严格的要求。

通常情况下，天然气系统的压力不得超过5 psi（34 kPa），除非满足以下所有条件：

当地权威机构允许更高的压力。

分配管道是焊接的。（注意：2. 一些地区可能还要求焊接接头进行射线检查以验证连续性）。

管道被封闭以保护，并放置在不允许气体积聚的通风区域。

管道安装在用于工业过程、研究、储存或机械设备房间的区域中。

通常情况下，允许的液化石油气最大压力为20 psi（140 kPa），前提是建筑物专门用于工业或研究目的，并按照NFPA 58：液化石油气代码第7章的要求建造[85]。

在地震地区，工作压力为55 psig（3.7 bar）的地震阀可以阻止天然气流入整个现场天然气分配管网（位于户外地下、建筑物屋顶上方或天篷屋顶的上部支撑内）。地震阀设计用于最大60 psig的情况[86][87]。

在澳大利亚，天然气从气体处理设施通过输气管道运输到调压站。然后将气体调节到分布压力，并通过气体主干分布到气体网络中。网络通常在7千帕（低压）到515千帕（高压）的压力范围内运行。然后将气体调节到1.1千帕或2.75千帕，然后进行计量，并供给消费者进行家庭用途[88]。天然气主干可以由各种材料制成：历史上是铸铁，但现代化的主干通常由钢或聚乙烯制成。

在美国的某些州，独立的天然气批发商/供应商可以通过现有的管道业主基础设施通过天然气选择计划供应天然气。

液化石油气（LPG）通常用于户外和便携式烧烤。然而，在美国的一些偏远地区，由于现有管道系统和分销网络较廉价且更丰富的液化石油气（LPG），压缩天然气（CNG）在类似的应用中供应非常有限。

A Washington, D.C. Metrobus, which runs on natural gas

Transportation[edit]

CNG is a cleaner and also cheaper alternative to other automobile fuels such as gasoline (petrol).^[89] By the end of 2014, there were over 20 million natural gas vehicles worldwide, led by Iran (3.5 million), China (3.3 million), Pakistan (2.8 million), Argentina (2.5 million), India (1.8 million), and Brazil (1.8 million).^[90] 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.^[91]

Besides use in road vehicles, CNG can also be used in aircraft.^[92] Compressed natural gas has been used in some aircraft like the Aviat Aircraft Husky 200 CNG^[93] and the Chromarat VX-1 KittyHawk^[94]

LNG is also being used in aircraft. Russian aircraft manufacturer Tupolev for instance is running a development program to produce LNG- and hydrogen-powered aircraft.^[95] The program has been running since the mid-1970s, and seeks to develop LNG and hydrogen variants of the Tu-204 and Tu-334 passenger aircraft, and also the Tu-330 cargo aircraft. Depending on the current market price for jet fuel and LNG, fuel for an LNG-powered aircraft could cost 5,000 rubles (US$100) less per tonne, roughly 60%, with considerable reductions to carbon monoxide, hydrocarbon and nitrogen oxide emissions.^{[citation needed]}

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.^{[citation needed]}

与汽油等其他汽车燃料相比，压缩天然气是一种更清洁、更便宜的替代品。[89]截至2014年底，全球天然气汽车保有量超过2000万辆，其中伊朗(350万辆)、中国(330万辆)、巴基斯坦(280万辆)、阿根廷(250万辆)、印度(180万辆)和巴西(180万辆)位居前列。[90]能源效率一般与汽油发动机相当，但与现代柴油发动机相比要低一些。改用天然气的汽油/汽油车由于其发动机的压缩比较低而受到影响，导致在使用天然气时输出功率下降(10-15%)。然而，cng专用发动机使用更高的压缩比，因为这种燃料的辛烷值更高，为120-130。[91]除了用于道路车辆，CNG也可用于飞机。[92]压缩天然气已经在一些飞机上使用，如Aviat aircraft Husky 200 CNG[93]和Chromarat VX-1 KittyHawk[94]，液化天然气也被用于飞机上。例如，俄罗斯飞机制造商图波列夫公司正在开展一项开发计划，生产液化天然气和氢动力飞机。[95]该项目自20世纪70年代中期以来一直在运行，旨在开发Tu-204和Tu-334客机的LNG和氢气改型，以及Tu-330货机。根据目前航空燃料和液化天然气的市场价格，液化天然气动力飞机的燃料每吨可节省5000卢布(100美元)，约占60%，一氧化碳、碳氢化合物和氮氧化物的排放量大幅减少。液态甲烷作为喷气发动机燃料的优点是它比标准的煤油混合物具有更多的比能，而且它的低温可以帮助冷却发动机压缩的空气，以获得更高的容积效率，实际上取代了中间冷却器。或者，它可以用来降低排气的温度。[引文需要]

Fertilizers[edit]

See also: 2007–2008 world food price crisis

Natural gas is a major feedstock for the production of ammonia, via the Haber process, for use in fertilizer production.^[82][96] The development of synthetic nitrogen fertilizer has significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use.^[97][98]

Hydrogen[edit]

See also: Industrial gas

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 vehicles.

Animal and fish feed[edit]

Protein rich animal and fish feed is produced by feeding natural gas to Methylococcus capsulatus bacteria on commercial scale.^{[99][100][101]}

Olefins(alkenes)[edit]

Natural gas components(alkanes) can be converted into olefins(alkenes) or other chemical synthesis. Ethane by oxidative dehydrogenation converts to ethylene, which can be further converted to ethylene oxide, ethylene glycol, acetaldehyde or other olefins. Propane by oxidative hydrogenation converts to propylene or can be oxidized to acrylic acid and acrylonitrile.

Other[edit]

Natural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, synthetic oil, and other products.^[102]

Fuel for industrial heating and desiccation processes.

Raw material for large-scale fuel production using gas-to-liquid (GTL) process (e.g. to produce sulphur-and aromatic-free diesel with low-emission combustion).

Environmental effects[edit]

See also: Environmental impact of the energy industry

Greenhouse effect and natural gas release[edit]

See also: Greenhouse effect, Atmospheric methane, Gas venting, and Fugitive gas emissionsThe warming influence (called radiative forcing) of long-lived greenhouse gases has increased substantially in the last 40 years, with carbon dioxide and methane being the dominant drivers of global warming.^[103]

Human activity is responsible for about 60% of all methane emissions and for most of the resulting increase in atmospheric methane.^{[104][105][106]} Natural gas is intentionally released or is otherwise known to leak during the extraction, storage, transportation, and distribution of fossil fuels. Globally, methane accounts for an estimated 33% of anthropogenic greenhouse gas warming.^[107] The decomposition of municipal solid waste (a source of landfill gas) and wastewater account for an additional 18% of such emissions. These estimates include substantial uncertainties^[108] which should be reduced in the near future with improved satellite measurements, such as those planned for MethaneSAT.^[12]

After release to the atmosphere, methane is removed by gradual oxidation to carbon dioxide and water by hydroxyl radicals (OH−
) formed in the troposphere or stratosphere, giving the overall chemical reaction CH
4 + 2O
2 → CO
2 + 2H
2O.^[109][110] While the lifetime of atmospheric methane is relatively short when compared to carbon dioxide,^[111] with a half-life of about 7 years, it is more efficient at trapping heat in the atmosphere, so that a given quantity of methane has 84 times the global-warming potential of carbon dioxide over a 20-year period and 28 times over a 100-year period. Natural gas is thus a potent greenhouse gas due to the strong radiative forcing of methane in the short term, and the continuing effects of carbon dioxide in the longer term.^[106]

Targeted efforts to reduce warming quickly by reducing anthropogenic methane emissions is a climate change mitigation strategy supported by the Global Methane Initiative.^[107]

Greenhouse gas emissions[edit]

When refined and burned, natural gas can produce 25–30% less carbon dioxide per joule delivered than oil, and 40–45% less than coal.^[112] It can also produce potentially fewer toxic pollutants than other hydrocarbon fuels.^[112][113] However, compared to other major fossil fuels, natural gas causes more emissions in relative terms during the production and transportation of the fuel, meaning that the life cycle greenhouse gas emissions are about 50% higher than the direct emissions from the site of consumption.^[114][115]

In terms of the warming effect over 100 years, natural gas production and use comprises about one fifth of human greenhouse gas emissions, and this contribution is growing rapidly. Globally, natural gas use emitted about 7.8 billion tons of CO
2 in 2020 (including flaring), while coal and oil use emitted 14.4 and 12 billion tons, respectively.^[116] The IEA estimates the energy sector (oil, natural gas, coal and bioenergy) to be responsible for about 40% of human methane emissions.^[117] According to the IPCC Sixth Assessment Report, natural gas consumption grew by 15% between 2015 and 2019, compared to a 5% increase in oil and oil product consumption.^[118]

The continued financing and construction of new gas pipelines indicates that huge emissions of fossil greenhouse gases could be locked-in for 40 to 50 years into the future.^[119] In the U.S. state of Texas alone, five new long-distance gas pipelines have been under construction, with the first entering service in 2019,^[120] and the others scheduled to come online during 2020–2022.^[121]: 23

Installation bans[edit]

To reduce its greenhouse emissions, the Netherlands is subsidizing a transition away from natural gas for all homes in the country by 2050. In Amsterdam, no new residential gas accounts have been allowed since 2018, and all homes in the city are expected to be converted by 2040 to use the excess heat from adjacent industrial buildings and operations.^[122] Some cities in the United States have started prohibiting gas hookups for new houses, with state laws passed and under consideration to either require electrification or prohibit local requirements.^[123] New gas appliance hookups are banned in New York State^[124] and the Australian Capital Territory.^[125] Additionally, the state of Victoria in Australia is set to implement a ban on new natural gas hookups starting from January 1, 2024, as part of its gas substitution roadmap.^[126]

The UK government is also experimenting with alternative home heating technologies to meet its climate goals.^[127] To preserve their businesses, natural gas utilities in the United States have been lobbying for laws preventing local electrification ordinances, and are promoting renewable natural gas and hydrogen fuel.^[128]

Other pollutants[edit]

Although natural gas produces far lower amounts of sulfur dioxide and nitrogen oxides (NOx) than other fossil fuels,^[113] NOx from burning natural gas in homes can be a health hazard.^[129]

Radionuclides[edit]

Natural gas extraction also produces radioactive isotopes of polonium (Po-210), lead (Pb-210) and radon (Rn-220). Radon is a gas with initial activity from 5 to 200,000 becquerels per cubic meter of gas. It decays rapidly to Pb-210 which can build up as a thin film in gas extraction equipment.^[130]

Safety concerns[edit]

A pipeline odorant injection station

The natural gas extraction workforce face unique health and safety challenges.^[131][132]

Production[edit]

Some gas fields yield sour gas containing hydrogen sulfide (H
2S), a toxic compound when inhaled. Amine gas treating, an industrial scale process which removes acidic gaseous components, is often used to remove hydrogen sulfide from natural gas.^[133]

Extraction of natural gas (or oil) leads to decrease in pressure in the 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.^[134]

Fracking[edit]

Main article: Environmental impact of hydraulic fracturing

Releasing natural gas from subsurface porous rock formations may be accomplished by a process called hydraulic fracturing or "fracking". Since the first commercial hydraulic fracturing operation in 1949, approximately one million wells have been hydraulically fractured in the United States.^[135] The production of natural gas from hydraulically fractured wells has used the technological developments of directional and horizontal drilling, which improved access to natural gas in tight rock formations.^[136] Strong growth in the production of unconventional gas from hydraulically fractured wells occurred between 2000 and 2012.^[137]

In hydraulic fracturing, well operators force water mixed with a variety of chemicals through the wellbore casing into the rock. The high pressure water breaks up or "fracks" the rock, which releases gas from the rock formation. Sand and other particles are added to the water as a proppant to keep the fractures in the rock open, thus enabling the gas to flow into the casing and then to the surface. Chemicals are added to the fluid to perform such functions as reducing friction and inhibiting corrosion. After the "frack", oil or gas is extracted and 30–70% of the frack fluid, i.e. the mixture of water, chemicals, sand, etc., flows back to the surface. Many gas-bearing formations also contain water, which will flow up the wellbore to the surface along with the gas, in both hydraulically fractured and non-hydraulically fractured wells. This produced water often has a high content of salt and other dissolved minerals that occur in the formation.^[138]

The volume of water used to hydraulically fracture wells varies according to the hydraulic fracturing technique. In the United States, the average volume of water used per hydraulic fracture has been reported as nearly 7,375 gallons for vertical oil and gas wells prior to 1953, nearly 197,000 gallons for vertical oil and gas wells between 2000 and 2010, and nearly 3 million gallons for horizontal gas wells between 2000 and 2010.^[139]

Determining which fracking technique is appropriate for well productivity depends largely on the properties of the reservoir rock from which to extract oil or gas. If the rock is characterized by low-permeability – which refers to its ability to let substances, i.e. gas, pass through it, then the rock may be considered a source of tight gas.^[140] Fracking for shale gas, which is currently also known as a source of unconventional gas, involves drilling a borehole vertically until it reaches a lateral shale rock formation, at which point the drill turns to follow the rock for hundreds or thousands of feet horizontally.^[141] In contrast, conventional oil and gas sources are characterized by higher rock permeability, which naturally enables the flow of oil or gas into the wellbore with less intensive hydraulic fracturing techniques than the production of tight gas has required.^[142][143] The decades in development of drilling technology for conventional and unconventional oil and gas production have not only improved access to natural gas in low-permeability reservoir rocks, but also posed significant adverse impacts on environmental and public health.^{[144][145][146][147]}

The US EPA has acknowledged that toxic, carcinogenic chemicals, i.e. benzene and ethylbenzene, have been used as gelling agents in water and chemical mixtures for high volume horizontal fracturing (HVHF).^[148] Following the hydraulic fracture in HVHF, the water, chemicals, and frack fluid that return to the well's surface, called flowback or produced water, may contain radioactive materials, heavy metals, natural salts, and hydrocarbons which exist naturally in shale rock formations.^[149] Fracking chemicals, radioactive materials, heavy metals, and salts that are removed from the HVHF well by well operators are so difficult to remove from the water they are mixed with, and would so heavily pollute the water cycle, that most of the flowback is either recycled into other fracking operations or injected into deep underground wells, eliminating the water that HVHF required from the hydrologic cycle.^[150]

Historically low gas prices have delayed the nuclear renaissance, as well as the development of solar thermal energy.^[151]

Added odor[edit]

Natural gas in its native state is colorless and almost odorless. In order to assist consumers in detecting leaks, an odorizer with a scent similar to rotten eggs, tert-Butylthiol (t-butyl mercaptan), is added. Sometimes a related compound, 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.^{[152][needs update]}

Risk of explosion[edit]

Gas network emergency vehicle responding to a major fire in Kyiv, Ukraine

Explosions caused by natural gas leaks 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. Leaks often result from excavation work, such as when contractors dig and strike pipelines, sometimes without knowing any damage resulted. Frequently, the blast is powerful 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, destroying one or more buildings in the process. Many building codes now forbid the installation of gas pipes inside cavity walls or below floor boards to mitigate against this risk. Gas usually dissipates readily outdoors, but can sometimes collect in dangerous quantities if flow rates are high enough.^[153] However, considering the tens of millions of structures that use the fuel, the individual risk of using natural gas is low.

Risk of carbon monoxide inhalation[edit]

Natural gas heating systems may cause carbon monoxide poisoning if unvented or poorly vented. Improvements in natural gas furnace designs have greatly reduced CO poisoning concerns. Detectors are also available that warn of carbon monoxide or explosive gases such as methane and propane.^[154]

Energy content, statistics, and pricing[edit]

Main article: Natural gas pricesSee also: Billion cubic metres of natural gasComparison of natural gas prices in Japan, United Kingdom, and United States, 2007–2011

This section needs to be updated. Please help update this article to reflect recent events or newly available information. (October 2022)

Quantities of natural gas are measured in standard cubic meters (cubic meter of gas at temperature 15 °C (59 °F) and pressure 101.325 kPa (14.6959 psi)) or standard cubic feet (cubic foot of gas at temperature 60.0 °F and pressure 14.73 psi (101.6 kPa)), 1 standard cubic meter = 35.301 standard cubic feet. The gross heat of combustion of commercial quality natural gas is around 39 MJ/m³ (0.31 kWh/cu ft), but this can vary by several percent. This is about 50 to 54 MJ/kg depending on the density.^[155][156] For comparison, the heat of combustion of pure methane is 37.7 MJ per standard cubic metre, or 55.5 MJ/kg.

Except in the European Union, the U.S., and Canada, natural gas is sold in gigajoule retail units. LNG (liquefied natural gas) and LPG (liquefied petroleum gas) are traded in metric tonnes (1,000 kg) or million BTU as spot deliveries. Long term natural gas distribution contracts are signed in cubic meters, and LNG contracts are in metric tonnes. The LNG and LPG is transported by specialized 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. The European Union aimed to cut its gas dependency on Russia by two-thirds in 2022.^[157]

In August 2015, possibly the largest natural gas discovery in history was made and notified by an Italian gas company ENI. The energy company indicated that it has unearthed a "supergiant" gas field in the Mediterranean Sea covering about 40 square miles (100 km²). This was named the Zohr gas field and could hold a potential 30 trillion cubic feet (850 billion cubic meters) of natural gas. ENI said that the energy is about 5.5 billion barrels of oil equivalent [BOE] (3.4×10¹⁰ GJ). The Zohr field was found in the deep waters off the northern coast of Egypt and ENI claims that it will be the largest ever in the Mediterranean and even the world.^[158]

European Union[edit]

Gas prices for end users vary greatly across the EU.^[159] A single European energy market, one of the key objectives of the EU, should level the prices of gas in all EU member states. Moreover, it would help to resolve supply and global warming issues,^[160] as well as strengthen relations with other Mediterranean countries and foster investments in the region.^[161] Qatar has been asked by the US to supply emergency gas to the EU in case of supply disruptions in the Russo-Ukrainian crisis.^[162]

United States[edit]

US Natural Gas Marketed Production 1900 to 2012 (US EIA data)Trends in the top five natural gas-producing countries (US EIA data)

In US units, one standard cubic foot (28 L) of natural gas produces around 1,028 British thermal units (1,085 kJ). The actual heating value when the water formed does not condense is the net heat of combustion and can be as much as 10% less.^[163]

In the United States, retail sales are often in units of therms (th); 1 therm = 100,000 BTU. Gas sales to domestic consumers are often in units of 100 standard cubic feet (scf). Gas meters 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. The typical annual consumption of a single family residence is 1,000 therms or one Residential Customer Equivalent (RCE). Wholesale transactions are generally done in decatherms (Dth), thousand decatherms (MDth), or million decatherms (MMDth). A million decatherms is a trillion BTU, roughly a billion cubic feet of natural gas.

The price of natural gas varies greatly depending on location and type of consumer. The typical caloric value of natural gas is roughly 1,000 BTU per cubic foot, depending on gas composition. Natural gas in the United States is traded as a futures contract on the New York Mercantile Exchange. Each contract is for 10,000 million BTU or 10 billion BTU (10,551 GJ). Thus, if the price of gas is $10/million BTU on the NYMEX, the contract is worth $100,000.

Canada[edit]

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Canada uses metric measure for internal trade of petrochemical products. Consequently, natural gas is sold by the gigajoule (GJ), cubic meter (m³) or thousand cubic meters (E3m3). Distribution infrastructure and meters almost always meter volume (cubic foot or cubic meter). Some jurisdictions, such as Saskatchewan, sell gas by volume only. Other jurisdictions, such as Alberta, gas is sold by the energy content (GJ). In these areas, almost all meters for residential and small commercial customers measure volume (m³ or ft³), and billing statements include a multiplier to convert the volume to energy content of the local gas supply.

A gigajoule (GJ) is a measure approximately equal to 80 litres (0.5 barrels) of oil, or 28 m³ or 1,000 cu ft or 1 million BTUs of gas. The energy content of gas supply in Canada can vary from 37 to 43 MJ/m³ (990 to 1,150 BTU/cu ft) depending on gas supply and processing between the wellhead and the customer.

Adsorbed natural gas (ANG)[edit]

Natural gas may be stored by adsorbing it to the porous solids called sorbents. The optimal condition for methane storage is at room temperature and atmospheric pressure. Pressures up to 4 MPa (about 40 times atmospheric pressure) will yield greater storage capacity. The most common sorbent used for ANG is activated carbon (AC), primarily in three forms: Activated Carbon Fiber (ACF), Powdered Activated Carbon (PAC), and activated carbon monolith.^[164]

See also[edit]

• Energy portal

• Renewable energy portal

• Associated petroleum gas

• Energy transition

• Gas/oil ratio

• Natural gas by country

• Peak gas

• Power-to-gas

• Renewable natural gas

• Strategic natural gas reserve

• World energy supply and consumption

References[edit]

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