Ethane analysis points to severe underestimation of methane emissions in oil and gas production

May 24, 2021
Oil rigs stand in the Loco Hills field near Artesia, New Mexico, one of the most active regions of the Permian Basin. (AP Photo/Jeri Clausing)

Oil rigs stand in the Loco Hills field near Artesia, New Mexico, one of the most active regions of the Permian Basin. (AP Photo/Jeri Clausing)

A new analysis of emissions from ethane, which are tied to methane emissions and largely attributable to oil and gas companies, shows that the U.S. Environmental Protection Agency is underestimating methane generated by the industry by 46% to 76%.

Researchers have long suggested that the EPA underestimates the level of methane emissions in the U.S., but pinpointing the sources of these emissions is difficult, given that methane comes from a variety of sources, including agriculture and wetlands. The new study, published May 5 in the Journal of Geophysical Research: Atmospheres, details a method of analyzing ethane emissions that links a previously underestimated share of methane emissions to the oil and gas industry, providing new information that could inform future climate change efforts. 

"As far as I'm aware, this is the only paper that's figured out that oil and gas methane emissions [estimates] are too low without actually measuring methane emissions," said lead author Zachary Barkley, an atmospheric scientist at Pennsylvania State University. "There is clearly an ethane/methane source here — oil and gas wells — which are being underestimated, and it needs to be accounted for."

Methane is an important greenhouse gas that traps heat 28 times more effectively than carbon dioxide over a 100-year span. According to the study, methane emissions stabilized in the early 2000s but have been increasing since 2007.

Oil and gas infrastructure is prone to methane leaks through valves and other equipment during production and extraction. Gas flares, a common industry practice, are also common sources of methane emissions. The EPA keeps an inventory of these emissions, but the agency's calculations tend to be based on old measurements, according to Barkley.

"We know CO2 a lot better than we know methane, and so that's raised a lot of alarm in part because a lot of the climate projections did not account for this methane increase," Barkley said in an interview with The Academic Times. "We're doing so much to try and offset CO2, and now we can barely offset the changes we're seeing to the methane, so there's this big rush to try and figure out what's causing it, and one of the big sectors that's been looked at is oil and gas."

The EPA classifies methane and ethane as "negligibly reactive" volatile organic compounds, or VOCs, which are any organic compounds that react with light in the atmosphere. As a result, the agency exempts methane and ethane from emissions limitations. In April, environmental groups including the Center for Biological Diversity petitioned the EPA to remove methane and ethane from its "negligibly reactive" list.

To generate a more accurate reading of methane emitted from oil and gas operations, Barkley and his colleagues decided to study ethane emissions. Scientists understand that ethane emissions mostly come from the oil and gas industry and, most important, accompany methane emissions. 

Detecting atmospheric ethane emissions has only become possible with new technologies, according to Barkley. To calculate methane emissions from ethane, Barkley and his colleagues drew on data collected from the recent NASA-funded Atmospheric Carbon and Transport - America, or ACT-America, mission that sent planes over various regions of the U.S. to study the sources of greenhouse gases.

The researchers used ethane emissions data from 200 ACT-America flight hours from 2017-19, and could then derive how much methane would typically accompany that amount of ethane. For example, if the EPA lists an oil-producing basin's methane content to be 100 grams, it would account for 10 grams of ethane, depending on the type of well. Barkley and his colleagues often found that the ethane readings from ACT-America indicated that the EPA's methane values were off by a factor of two, meaning that the aforementioned 100 grams of methane would really be closer to 200. 

"What happens when you do these studies with methane is you end up reporting your results, and then the oil and gas company will come after you and say, 'Well, how do you know it wasn't a cow? How do you know it wasn't a landfill?'" Barkley said. "When you only use ethane, no methane, and you come up with the same result as all these other papers that show that the EPA inventory is off, it just completely kills that argument, because there's nothing else it can be coming from."

While Barkley's study pertains to the oil and gas industry, agriculture, especially livestock, is responsible for a substantial amount of methane emissions as well. A study from March published in PLOS ONE described how feeding cows red seaweed can dramatically reduce their methane emissions. 

Barkley is currently studying the Permian Basin, a large sedimentary basin located in Texas and part of New Mexico that produces over 4 million barrels of oil a day as of 2021. He and his colleagues set up a network of five towers to continuously measure methane emissions in the basin in March 2020. The initial readings steeply declined, according to Barkley, as "society collapsed" around that time, but have since steadied.

Continuous measurements can help reveal how emissions are changing over time, according to Barkley. Those from ACT-America, on the other hand, can only show emissions from a specific point in time, such as when one of its planes flew over a specific airspace. 

The research, according to Barkley, is another step in trying to push the EPA to hold oil and gas companies accountable for their methane emissions. 

"All you can do is just keep putting these papers out there and keep putting pressure on them, just to emphasize over and over that something's clearly wrong," he said. 

The study, "Analysis of oil and gas ethane and methane emissions in the Southcentral and Eastern United States using four seasons of continuous aircraft ethane measurements," published May 5 in Journal of Geophysical Research: Atmospheres, was authored by Z.R. Barkley, K.J. Davis and Y.Y. Cui, The Pennsylvania State University; S. Feng, The Pennsylvania State University and Pacific Northwest National Laboratory; A. Fried, P. Weibring, D. Richter and J.G. Walega, University of Colorado, Boulder; S.M. Miller, Johns Hopkins University; and M. Eckl, A. Roiger, A. Fiehn and J. Kostinek, Institut für Physik der Atmosphäre.

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