EPA estimates of methane emissions from oil and natural gas facilities are based on aircraft observations and facility-scale measurements. The estimated amount is roughly equivalent to 13+-2 Tg/y, or 2.3% of gross U.S. gas production. However, these estimates may not reflect actual emissions because they do not account for abnormal operating conditions. In addition, methane emissions cause radiative forcing over the course of 20 years.
Estimates of methane emissions
There are many factors that contribute to the emission of methane, including oil and gas production. These sources are often hard to measure directly. Instead, methane emissions are usually estimated based on equipment installed at oil and gas facilities. These estimates, however, do not capture all emissions and are not necessarily an accurate representation of individual facilities.
These estimates may not be precise and depend on manual manipulation of base year data. Moreover, they may be affected by changes in spatial distribution of production. For example, Pennsylvania has been importing natural gas before it started a production boom, which has changed its emissions profile. Other factors that influence the emissions of natural gas include the directionality of pipelines and the seasonality of production.
The most sensitive regions of the US to emissions of methane are California and the Pacific Northwest. However, estimates for the Midwest and New England are sensitive to production stage methane emissions from Canadian natural gas. As a result, sensitivity analysis should be conducted for these regions.
Estimates of natural gas methane are important for climate change policy. The variability in these emissions is often large enough to be decision-relevant. Moreover, if we have formal targets for reducing GHGs, assessing methane emissions in the natural gas supply chain will be increasingly important.
The emission rate from production stage is approximately 16% to 65% of the total emissions of carbon dioxide. Other sources contribute in similar magnitude. The intensity of production-stage methane emissions is highest in Arizona, Kansas, and New Mexico, largely due to reliance on high-emission basins. However, the data are not comparable across studies, and the assumptions used to calculate them are not uniform.
Estimates of natural gas methane emission are hard to come by, since it is difficult to quantify the leakage rate. However, in a recent study coordinated by the EDF, the leakage rate for U.S. oil and gas is 2.3%, which is 60% more than the EPA’s estimate. This is particularly significant in the Permian Basin, which accounts for nearly 30% of the country’s oil and 10% of its gas output.
The methane charge is also affected by differences in the amount of emissions of natural gas between companies. Depending on the regional natural gas prices, companies that have higher emissions are negatively affected by the methane charge. As a result, they must absorb higher costs or limit their output.
The oil and gas industry is placing increasing emphasis on methane reduction and has set aside a $1 billion fund to fund projects. According to the Oil and Gas Climate Initiative, a group of 12 companies pledged to cut their methane intensity by 9%. The report concluded that gas loses its climate benefits when the leakage rate exceeds 2.7% of its production.
While natural gas production has increased by 40% in the United States since 1995, the emission of CH4 has decreased only by 16%. This is largely due to technology advancements and improvements in the extraction process. However, natural gas and coal production remain major sources of CH4 globally. As a result, further research is needed to determine the actual impact of these emissions on climate.
Seasonality of methane emissions
We have recently examined the seasonal variation of natural gas methane emissions. The results indicated that the emissions are greater during the growing season and lower during the non-growing season. The seasonal variation of methane emissions in Canada was 2.1 + 0.8% yr-1 in June and 1.7 + 0.6% yr-1 in July. We also noted that these changes were associated with higher air temperatures, which is probably a contributor to the early summer increases.
Methane fluxes are strongly influenced by seasonal air temperatures, especially during the early summer, while the effects of soil temperatures are most significant later in the year. This suggests that air temperature and methane fluxes follow the same physical transport processes. During the thawing season, graminoid plants begin to grow, which facilitates upward methane transport. This increase in fluxes reaches its highest level in early August when the ground thaws to a depth of 50 cm. During the subsequent drop in September, the rate of change is more noticeable than during the previous rise.
The increasing methane emissions from thawing permafrost are expected to contribute to climate change. While the effects of these emissions are not well understood, they are expected to be a large contributor. Our findings are consistent with observations of natural gas methane emissions at wetlands. We note that seasonal methane emissions are highly variable and vary considerably within the same site.
The study conducted in the Arctic also found that methane emissions were most strongly related to plant growth, which is linked to the availability of substrates for methanogens. The results show that plant growth is a critical factor in controlling the seasonal variability of natural gas emissions. Moreover, the height of the water table and availability of labile organic compounds are important factors that influence the amount of methane produced in wetlands.
In addition, the seasonality of methane emissions in the Permian Basin is related to the amount of natural gas produced. During an 11-month period, the production of natural gas in the Permian Basin increased by about 20%. Further investigation is needed to determine the factors that influence the temporal variability of natural gas methane emissions.
The study also found that methane emissions from natural gas are larger than previously thought. Researchers estimated that natural gas emissions may be two to three times higher than the 6 percent implied by the most closely comparable emission inventory. This represents an important loss of resource. This study is based on government data and geospatial information.
The methane emissions from oil and gas systems account for about 30 percent of all human-made methane emissions in the U.S. While methane is less of a greenhouse gas than carbon dioxide, it is still a powerful greenhouse gas. Its atmospheric lifetime is significantly shorter than CO2, and it absorbs more energy.
Impact of methane emissions on carbon dioxide emissions
Natural gas methane emissions come from various parts of the natural gas supply chain. This includes wells, pipelines, processing facilities and storage tanks. The United States Environmental Protection Agency estimates that natural gas and petroleum systems contributed to nearly 29% of the nation’s total methane emissions in 2019. Oil and gas producers are taking steps to prevent natural gas leaks.
The cost of methane abatement varies depending on the level of emissions and the regional price of natural gas. The cost of abatement will be greater for companies that produce more methane than other companies. However, the amount of additional expense is expected to be passed on to the end user. The increased costs will reduce natural gas consumption, thereby reducing methane emissions.
Although methane is only a small fraction of the atmosphere, it has a large impact on the climate. It traps heat in the atmosphere for the first 20 years, unlike CO 2. Methane also breaks down much faster than CO 2. Therefore, reducing methane emissions will benefit the climate in the short-term.
Methane is a primary greenhouse gas, trapping more heat and releasing it more quickly than CO2. The difference in heat trapping power between the two gases is large, so scientists convert methane emissions to carbon dioxide equivalents to assess their impact on carbon dioxide emissions. Methane is 30 times more potent than carbon dioxide over a century, and 80 times stronger over twenty years. The EPA uses a 100-year conversion to calculate the global impact of methane.
Upstream methane emissions are one major cause of natural gas leakage, and they have significant effects on climate. If you want to reduce carbon dioxide emissions, the upstream methane leakage rate must be reduced as well. If the leakage rate of natural gas is too high, it will eliminate any advantage natural gas has over coal. A robust GHG reduction strategy needs to take into account the upstream emissions of all fuels.
Methane emissions are difficult to measure because of the multiple points of emissions throughout the supply chain. Nonetheless, these emissions can be significant and impact companies’ costs and downstream prices. But it is important to note that the amount of methane a company releases will be directly affected by the way the emissions are measured.
The EU is working on a strategy to reduce methane emissions that will target the energy, waste and agriculture sectors. This strategy will focus on synergies between these sectors and emphasize international collaboration to reduce emissions. The Commission recently launched a roadmap for public feedback, which will close on 12 August 2020.
To estimate methane emissions, scientists have used satellites and airborne surveys. They have found that emissions from a small number of sources account for a large portion of the emissions.
