Methane belongs to a class of so-called “super pollutants” that simultaneously contribute to climate change and degrade the health of people and ecosystems. It has about 30 times the impact on global warming per unit mass compared to carbon dioxide over a 100-year lifetime (83 times larger over 20 years).1 Methane is responsible for about 30% of the rise in global temperatures since the Industrial Revolution.2
Methane is a precursor to ground-level ozone (tropospheric ozone), a major component of smog. High ozone levels can cause respiratory problems, aggravate asthma, and reduce lung function. Ozone also reduces the productivity of crops and forests. Methane is highly flammable, posing serious explosion risks in underground mining operations or gas pipelines.
About one-third of anthropogenic methane emissions originate in the fossil fuel supply chain.3 The “upstream” segment of the oil and gas supply chain involves exploration, drilling and production, and on-site treatment of raw oil and gas (e.g., separating oil, gas, and water). The “midstream” segment includes the transportation, storage, and processing. Key technologies are pipelines, liquified natural gas (LNG) terminals, and compressor stations. The “downstream” segment refines crude oil and natural gas into useful products (e.g., motor gasoline and dry natural gas) and delivers them to end users. Key technologies include refinery equipment, storage tanks, and retail distribution systems.
Methane emissions from oil and gas activities come from three main sources:4
- Fugitive emissions are the unintentional release (leaks) of natural gas (primarily methane) during extraction, production, storage, and transportation. They originate from storage tanks, compressors, wells, pressure release valves, and other equipment.
- Venting is the deliberate release of natural gas directly into the atmosphere. This typically occurs when it is not feasible, economical, or safe to capture, use, or process the gas.
- Flaring is the controlled burning of natural gas that is released during oil and gas production. This process is often used as an alternative to venting and is intended to reduce the direct release of methane into the atmosphere.
Methane emissions from coal mining occur when methane, which is naturally present in coal seams, is released into the atmosphere during the mining process. In underground coal mining, ventilation systems that maintain safe working conditions often vent methane directly into the atmosphere. Surface coal mining is less methane-intensive than underground mining, but methane is released when coal seams are exposed and disturbed during surface mining operations. Abandoned or closed mines release methane from diffuse vents, ventilation pipes, boreholes, or fissures in the ground. Additional methane escapes during the processing, transportation, and storage of coal.5
A marginal abatement cost curve (MACC) illustrates the cost-effectiveness of different measures to reduce (or “abate”) methane emissions from the fossil fuel supply chains. The vertical axis of a MACC represents the cost of abating one additional unit of emissions (e.g., $ per ton of CO₂-equivalent, or $ per BTU of fuel produced). The horizontal axis shows the cumulative quantity of emissions (kilotons of methane) that can be reduced by adopting various measures.
Abatement measures with negative costs reduce emissions and save money–the proverbial win-win outcome. Measures with positive costs require additional investment or incur expenses that may not be fully offset by savings or revenues. The International Energy Agency assessed a wide range of technologies and concluded that about 70% of methane emissions from fossil fuel operations could be reduced with existing technology.6
The IEA estimates that it is technically possible to avoid more than half of global methane emissions from coal operations today with existing technologies. Reducing ventilation air methane emissions (VAM) from underground coal mines offers the largest abatement opportunity. Ventilation systems are designed to dilute methane to safe levels to prevent explosions, but this also results in large volumes of low-concentration methane being emitted to the atmosphere.
Oxidation is a large potential source of VAM reduction. Methane reacts with oxygen in an oxidation reaction to form carbon dioxide and water vapor. The low concentration of methane in VAM (0.1% to 1% methane by volume) requires capital and operational costs that may be prohibitive in some cases.
The recovery of methane for productive use as a fuel is a second major abatement opportunity in underground mines. This is typically by a drainage system in which wells or boreholes are drilled into the coal seams or surrounding strata to release and capture methane. The captured methane is transported via pipelines for processing and utilization as fuel for power generation, heating, or industrial applications.7 Note that many opportunities for coal mine methane utilization have negative abatement costs, meaning that they are “win-win.” The global warming impact of methane emissions is reduced, and the captured methane is put into a productive economic activity.
The IEA estimates that it is technically possible to avoid more than 75% of global methane emissions from oil and gas operations today with existing technologies. The biggest opportunity with the lowest cost is leak detection and repair (LDAR). As the name suggests, this refers to the systematic identification, measurement, and repair of leaks in equipment and infrastructure such as pipelines, valves, compressors, storage tanks, and processing equipment.
Leak detection is performed by an array of technologies. Handheld analyzers called “sniffers” detect methane concentration near potential leak points. Unmanned drone and aerial systems can be equipped with methane sensors for remote detection. Advanced satellite systems can detect large-scale leaks over wide areas.8
Another area with big abatement potential in oil and gas is the replacement or repair of vapor recovery units (VRU). Vapors containing methane and other hydrocarbons accumulate in oil and condensate storage due to temperature changes and pressure fluctuations. The VRU compresses low-pressure vapors to higher pressure, separates them into liquid and gas components, returns the liquid portion to the storage tank, and captures the methane for processing and eventual use as a fuel.
Flares in oil and gas production are a direct source of methane emissions, because they do not completely combust all the hydrocarbons in the gas stream and because they are not continuously lit.9 The so-called “flare destruction efficiency” can be improved by using high quality burners, installing wind shields, maintaining an adequate supply of oxygen for complete combustion, and better monitoring.
LDAR and VRU are in the win-win category of abatement technologies. They reduce methane emissions and yield a valuable stream of fuel for heat or electricity generation.
1 Intergovernmental Panel on Climate Change (IPCC). The Earth’s Energy Budget, Climate Feedbacks and Climate Sensitivity. In: Climate Change 2021 – The Physical Science Basis: Working Group I Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press; 2023:923-1054, https://tinyurl.com/47wh3sbm
2 International Energy Agency, “Global Methane Tracker 2024,” March, 2024, https://www.iea.org/reports/global-methane-tracker-2024
3 International Energy Agency, op. cit.
4 World Bank Group, “Methane from Oil and Gas Production Explained, accessed December 15, 2024, Link
5 U.S. Environmental Protection Agency, “About Coal Mine Methane,” accessed December 14, 2024, https://www.epa.gov/cmop/about-coal-mine-methane
6 International Energy Agency, “Methane Abatement,” accessed December 14, 2024, https://www.iea.org/fuels-and-technologies/methane-abatement
7 U.S. Environmental Protection Agency, “Sources of Coal Mine Methane,” accessed December 14, 2024, https://www.epa.gov/cmop/sources-coal-mine-methane
8 MethaneSAT, https://www.methanesat.org/satellite
9 Caulton, Dana R., Paul B. Shepson, Maria O. L. Cambaliza, David McCabe, Ellen Baum, and Brian H. Stirm. “Methane Destruction Efficiency of Natural Gas Flares Associated with Shale Formation Wells.” Environmental Science & Technology 48, no. 16 (August 19, 2014): 9548–54. https://doi.org/10.1021/es500511w.