{{Short description|Unintended escape of methane from containment}} [[File:TKM TROPOMI Methane.png|thumb|Methane plume over Turkmenistan, 2020 image from the [[Sentinel-5 Precursor]] satellite]] A '''methane leak''' is a significant [[natural gas]] leak. The term is used for a class of [[methane emissions]], which can come from an industrial facility or pipeline.
Satellite data enables the identification of '''super-emitter events''' (synonymous with ultra-emitters, see "Mitigation of Ultra-Emitters") that produce '''methane plumes'''. Over 1,000 methane leaks of this type were found worldwide in 2022.<ref name="G0323">{{cite news |last1=Carrington |first1=Damian |title=Revealed: 1,000 super-emitting methane leaks risk triggering climate tipping points |url=https://www.theguardian.com/environment/2023/mar/06/revealed-1000-super-emitting-methane-leaks-risk-triggering-climate-tipping-points |work=The Guardian |date=6 March 2023}}</ref> As with other [[gas leak]]s, a leak of [[methane]] is a safety hazard: [[coalbed methane]] in the form of [[fugitive gas emission]] has always been a danger to miners.<ref>{{Cite web |last=US EPA |first=OAR |date=2015-12-08 |title=About Coal Mine Methane |url=https://www.epa.gov/cmop/about-coal-mine-methane |access-date=2025-04-14 |website=[[United States Environmental Protection Agency]] |language=en}}</ref> Methane leaks also have a serious environmental impact. Natural gas contain methane, [[ethane]], and other gases, which from the safety and environmental point of view raise major issues with atmospheric composition and human health.
As a [[greenhouse gas]] and [[climate change]] contributor, methane ranks second, following [[carbon dioxide]].<ref>{{Cite web |title=Methane {{!}} Vital Signs |url=https://climate.nasa.gov/vital-signs/methane/?intent=121 |access-date=2025-04-14 |website=Climate Change: Vital Signs of the Planet |language=en}}</ref> [[Fossil fuel]] exploration, transportation and production is responsible for about 40% of human-caused methane emissions.<ref name="G0323" /> Smaller leaks than can be spotted from space comprise [[long tail]] of emissions. They can be identified from planes flying at {{convert|900|meters}}.<ref>{{cite web |title=In Plane Sight: How to measure methane leaks |url=https://www.climateinvestment.com/news/in-plane-sight-how-to-measure-methane-leaks |website=Climate Investment |date=30 November 2021}}</ref> According to [[Fatih Birol]] of the [[International Energy Agency]], "Methane emissions are still far too high, especially as methane cuts are among the cheapest options to limit near-term global warming".<ref name="G0323"/>
==Examples of methane leaks== Individual methane leaks are reported as specific events with a large quantity of gas released. An example followed the [[2022 Nord Stream pipeline sabotage]]. Following early reports that the escape might exceed 10<sup>5</sup> tonnes, The [[International Methane Emissions Observatory]] of the [[United Nations Environment Programme]] analyzed the release. In February 2023 it put the mass of methane gas in the range 7.5 to 23.0 × 10<sup>4</sup> [[tonne]]s. In terms of overall [[Greenhouse gas emissions|human-made]] methane emissions, these figures are under 0.1% of the annual total.<ref>{{cite news |last1=McVeigh |first1=Karen |last2=Oltermann |first2=Philip |title=Nord Stream gas leaks may be biggest ever, with warning of 'large climate risk' |url=https://www.theguardian.com/environment/2022/sep/28/nord-stream-methane-gas-leaks-may-be-biggest-ever-with-warning-large-climate-risk |work=The Guardian |date=28 September 2022}}</ref><ref>{{cite web |title=UNEP finds Nord Stream gas leak may be the highest methane emission event, but still a drop in the ocean |url=https://www.unep.org/technical-highlight/unep-finds-nord-stream-gas-leak-may-be-highest-methane-emission-event-still |website=UNEP - UN Environment Programme |language=en |date=20 February 2023}}</ref>
Satellite data detection has shown that methane super emitter sites in [[Turkmenistan]], [[USA]] and [[Russia]] are responsible for the biggest number of events from fossil fuel facilities. Estimated emissions from oil and gas ultra-emitters rank highest for Turkmenistan with 1.3 megatons (Mt) of methane per year, followed by Russia, the United States, [[Iran]], Kazakhstan, and [[Algeria]].<ref name=":0">{{Cite journal |last1=Lauvaux |first1=T. |last2=Giron |first2=C. |last3=Mazzolini |first3=M. |last4=d'Aspremont |first4=A. |last5=Duren |first5=R. |last6=Cusworth |first6=D. |last7=Shindell |first7=D. |last8=Ciais |first8=P. |date=2022-02-04 |title=Global assessment of oil and gas methane ultra-emitters |url=https://www.science.org/doi/10.1126/science.abj4351 |journal=Science |volume=375 |issue=6580 |pages=557–561 |doi=10.1126/science.abj4351|pmid=35113691 |arxiv=2105.06387 |bibcode=2022Sci...375..557L }}</ref> Equipment failures are normally responsible for the releases, which can last for weeks.<ref name="UNEP">{{cite news |title=How secretive methane leaks are driving climate change |url=https://www.unep.org/news-and-stories/story/how-secretive-methane-leaks-are-driving-climate-change |work=UNEP |date=19 July 2022 |language=en}}</ref>
The [[Aliso Canyon gas leak]] of 2015 has been quantified as at least 1.09 × 10<sup>5</sup> tonnes of methane.<ref>{{cite web |title=Aliso Canyon Natural Gas Leak, California Air Resources Board |url=https://ww2.arb.ca.gov/our-work/programs/aliso-canyon-natural-gas-leak/about |website=ww2.arb.ca.gov}}</ref> Satellite data for the [[Raspadskaya coal mine]], [[Kemerovo Oblast]], Russia indicated in 2022 an hourly methane leakage rate of 87 tonnes;<ref>{{cite news |last1=Fountain |first1=Henry |title=One Site, 95 Tons of Methane an Hour |url=https://www.nytimes.com/2022/06/14/climate/methane-emissions-russia-coal-mine.html |work=The New York Times |date=14 June 2022}}</ref> this compares to 60 tonnes per hour of natural gas leaking from the Aliso Canyon incident, considered among the worst recorded leak events.<ref>{{cite news |last1=Milman |first1=Oliver |title=LA gas leak: worst in US history spewed as much pollution as 600,000 cars |url=https://www.theguardian.com/environment/2016/feb/26/los-angeles-aliso-canyon-gas-leak-methane-largest-us-history |work=The Guardian |date=26 February 2016}}</ref>
[[Spain]]'s [[Technical University of Valencia]], in a study published in 2022, found that a super emitter event at a gas and oil platform in the [[Gulf of Mexico]] released around 4 × 10<sup>4</sup> tonnes of [[methane]] during a 17-day time period in December 2021 (hourly rate around 98 tonnes).<ref>{{cite web |title=Methane emissions detected over offshore platform in the Gulf of Mexico |url=https://www.esa.int/Applications/Observing_the_Earth/Methane_emissions_detected_over_offshore_platform_in_the_Gulf_of_Mexico |website=www.esa.int |language=en}}</ref> Another major event in 2022 was a leak of 427 tonnes an hour in August, near Turkmenistan's [[Caspian Coastal Pipeline|Caspian coast]] and a major pipeline.<ref name="UNEP"/>
== Mitigation of Ultra-Emitters == Ultra-emitters of methane are characterized by producing more than 25 tons/hour of CH<sub>4</sub> from oil and gas activities, and are in the top 1% of methane emitters in the world.<ref name=":0" /> Reducing emissions from these sites can be done by enforcing leak detection and by reducing venting during routine maintenance.<ref name=":0" />
Ultra-emitters are common and particularly large in Russia, Iran, and Kazakhstan, representing 10-20% of annual reported emissions across the globe.<ref name=":0" /> The U.S. is found to house 5% of annual worldwide emissions, but this number excludes emissions from drilling in the Permian basin, which accounts for 10% of U.S. natural gas production.<ref name=":0" /> Drilling in the Permian basin creates about 2.7 Mt a year of emissions, which is 35% of U.S. oil and gas production emissions.<ref name=":0" />
Spending for mitigation of ultra-emitters is funded by the [[International Energy Agency|International Energy Agency (IEA)]], [[United States Environmental Protection Agency|Environmental Protection Agency (EPA)]], and [[International Institute for Applied Systems Analysis|International Institute for Applied Systems Analysis (IIASA)]].<ref name=":0" /> Emissions from ultra-emitters are expected to be more cost-effective to mitigate than average-sized sources due to efficiency and leak efforts.<ref name=":0" />
== Leakage from Abandoned Oil and Gas Wells == The geographic area of Lubbock has been a site of ongoing emissions research to assess the extent and environmental implications of methane leakage from abandoned wells.<ref name=":1">{{Cite journal |last1=Opara |first1=Stanley U. |last2=Okere |first2=Chinedu J. |date=2024-07-01 |title=A review of methane leakage from abandoned oil and gas wells: A case study in Lubbock, Texas, within the Permian Basin |url=https://linkinghub.elsevier.com/retrieve/pii/S2666759224000039 |journal=Energy Geoscience |volume=5 |issue=3 |article-number=100288 |doi=10.1016/j.engeos.2024.100288 |issn=2666-7592|hdl=2346/97724 |hdl-access=free }}</ref> Lubbock is located within the Permian Basin in West Texas, United States, and includes an estimate of 1781 drilling wells.<ref name=":1" /> Aeromagnetic surveys are used to detect active and abandoned wells and are able to detect those with no visible aboveground markers.<ref name=":1" /> Regular monitoring and repair initiatives targeting emissions from storage tanks can be particularly impactful in mitigating vented emissions.<ref name=":1" /> Even with efforts to accurately measure the greenhouse gas emissions associated with the abandoned wells, emissions data is still relatively uncertain due to gas characterization and source concerns.<ref name=":1" />
== Methane Detection Sensors == Usage of methane gas detection sensors vary based on region, environmental conditions, and purpose of measurements. Types of sensors include optical sensors, calorimetric sensors, pyroelectric sensors, semiconducting oxide sensors, and electrochemical sensors.
=== Optical Sensors === [[Optical sensor|Optical sensors]] detect changes in [[light waves]] that interact with the receptor. They are optimal in regions where there could be [[electromagnetic interference]] and at high altitudes where oxygen content is low.<ref name=":2">{{Cite journal |last1=Aldhafeeri |first1=Tahani |last2=Tran |first2=Manh-Kien |last3=Vrolyk |first3=Reid |last4=Pope |first4=Michael |last5=Fowler |first5=Michael |date=2020-07-06 |title=A Review of Methane Gas Detection Sensors: Recent Developments and Future Perspectives |journal=Inventions |language=en |volume=5 |issue=3 |page=28 |doi=10.3390/inventions5030028 |doi-access=free |issn=2411-5134}}</ref> They are also non-destructive and result in little to no environmental harm. However, they have high costs in large settings and low selectivity.<ref name=":2" />
=== Calorimetric Sensors === Calorimetric sensors measure the heat produced from a reaction and compare the value to reactant concentration.<ref name=":2" /> These sensors are low cost and have a simple design. They are able to operate in harsh conditions but are susceptible to cracking and accelerated degradation.<ref name=":2" /> They also require high power consumption to operate and have low detection accuracy.
=== Pyroelectric Sensors === Pyroelectric sensors convert [[thermal energy]] into [[electrical energy]] based on [[pyroelectricity]].<ref name=":2" /> They have good sensitivity and responsivity, can operate without oxygen, and have a wide measuring range. Among the limitations of pyroelectric sensors are cost and difficulty in manufacturing, but the most detrimental is the immobility of the sensor once positioned.<ref name=":2" />
=== Semiconducting Metal Oxide Sensors === Semiconducting metal oxide sensors measure methane by detecting the [[Absorption spectroscopy|absorption]] of gas on the surface of a [[metal oxide]], which changes its [[Conductivity (electrolytic)|conductivity]].<ref name=":2" /> These instruments are low cost, lightweight, and have a long lifespan. They may not be used as widely due to their poor selectivity, sensitivity to changes in temperature and humidity, and significant additive dependence.<ref name=":2" />
=== Electrochemical Sensors === Electrochemical sensors [[oxidize]] or reduce the gas detected at an [[electrode]] and measure the current to find methane gas concentration.<ref name=":2" /> These instruments are low cost, non-hazardous, and have low volatility. They also have good selectivity specifically for methane gas and can detect small leaks. They may have slow response time or be susceptible to degradation or loss of electrodes, however these sensors have returned promising results in the accuracy of small methane leak detection.<ref name=":2" />
== Units == Quantitative reports of methane leaks often use the [[standard cubic foot]] (scf) of the [[United States customary system]]. Applied to natural gas, a complex mixture of uncertain proportions, and depending on pressure and temperature conditions, the accuracy of calculations converting scf to metric units of mass is subject to limitations. A conversion figure given is 5 × 10<sup>4</sup> scf of natural gas as {{convert|1.32|short ton}}.<ref>{{cite web |title=Conversion of volume of natural gas to mass of natural gas |url=https://cimarron.com/conversion-of-volume-of-natural-gas-to-mass-of-natural-gas/ |website=Cimarron |date=12 January 2021}}</ref>
For detection sensitivity, quantitative criteria are typically stated in units of standard cubic feet per hour (scf/h, "skiff", US), or thousand standard cubic feet per day (Mscf/d); or with metric units kilograms per hour (kg/hr), cubic meters per day (m3/d).<ref>{{cite web |title=Understanding Methane Detection Sensitivity, Bridger Photonics |url=https://www.bridgerphotonics.com/blog/understanding-methane-detection-sensitivity |website=www.bridgerphotonics.com}}</ref> [[File:Tracking methane with EMIT and AVIRIS-3 (SVS5389).webm|thumb|Methane Tracking in the Permian Basin using EMIT and AVIRIS-3]] To describe the mass balance of methane in the atmosphere, mass rates are described in units of Tg/yr, i.e. [[Megatonne|teragram]]s per year where a teragram is 10<sup>6</sup> tonnes (megagrams).<ref>{{cite book |last1=Khalil |first1=M. A. K. |title=Atmospheric Methane: Sources, Sinks, and Role in Global Change |date=29 June 2013 |publisher=Springer Science & Business Media |isbn=978-3-642-84605-2 |page=173 |url=https://books.google.com/books?id=tbXtCAAAQBAJ&pg=PA173 |language=en}}</ref> The methane leak from the [[Permian Basin (North America)|Permian Basin]], a significant region of the [[Mid-Continent Oil Producing Area]], was estimated for 2018/9 from satellite data as 2.7 Tg/yr. Quoted in terms of the proportion of the mass of extracted gas, the leakage comes to 3.7%.<ref>{{cite news |last1=Gramling |first1=Carolyn |title=Permian Basin is leaking twice as much methane as once thought, Science News |url=https://www.sciencenews.org/article/permian-basin-oil-region-leaking-twice-methane-once-thought |date=22 April 2020}}</ref> The 2021 Carbon Mapper project, a collaboration of the [[Jet Propulsion Laboratory]] and academia, detected 533 methane super-emitters in the Permian Basin.<ref>{{cite news |title=Hidden Menace: Massive methane leaks speed up climate change |url=https://apnews.com/article/science-texas-trending-news-climate-and-environment-0eb6880f7c4532a845155a3bd44c2e4b |work=AP News |date=28 July 2022 |language=en}}</ref>
== References == {{reflist}}
[[Category:Greenhouse gas emissions]] [[Category:Methane]] [[Category:Natural gas safety]]