By Fangzhou Liu
According to a new study co-authored by energy resources engineering professor Adam Brandt, the greater part of methane emissions in the United States can be traced to a small number of “super-emitting” natural gas wells.
Published online in the journal Environmental Science & Technology, the findings suggests that companies can combat carbon emissions more effectively by focusing on tackling the biggest emitters among gas leaks, rather than searching for all leaks.
“We’re finding that when it comes to natural gas leaks, a 50/5 rule applies — that is, the largest 5 percent of leaks are typically responsible for more than 50 percent of the total volume of leakage,” said Brandt, an assistant professor at Stanford’s School of Earth, Energy & Environmental Sciences.
Natural gas well leaks are so damaging because they consist largely of methane, which is about 30 times more effective at trapping heat than carbon dioxide over a 100-year period. The problem is especially acute since natural gas is becoming increasingly important in meeting energy needs worldwide, and some think that natural gas could serve as a “bridge fuel” for countries during the transition from fossil fuels to renewable energy.
In their study, Brandt and his colleagues applied a statistical technique called extreme value theory, which is able to analyze infrequent but highly impactful events, to some 15,000 measurements from 18 prior studies of natural gas leaks around the U.S.
“Extreme value theory has been used to study everything from major flood events to crop losses brought on by drought and stock market crashes,” Brandt said. “In all of these cases, infrequent events really drive a lot of decision-making and expenditure or have big economic consequences. We are the first to apply this technique in a formal and rigorous way to natural gas leaks.”
Their analysis revealed that a few outsized leaks caused between 40 and 90 percent of the emissions, showing that the effect of methane emissions is more prevalent and extreme than previously known. As a result, eliminating “super-emitters” that contribute disproportionately to emissions could be a useful strategy for reducing total methane emissions in the U.S.
“If companies can identify and fix the leaks in a small number of top emitters, that will go a long way toward reducing methane emissions in the U.S.,” Brandt said.
According to Brandt, the study suggests that the U.S. could potentially reduce emissions even without the use of expensive super-sensitive leak detectors, since large, more easily detectable leaks are the main target.
Brandt is a member of the campus-wide Natural Gas Initiative (NGI), which supports projects related to surge in natural gas production over the past decade. Garvin Heath, from the National Renewable Energy Laboratory in Golden, Colorado, and Daniel Cooley, from Colorado State University in Fort Collins, also contributed to the project, which was funded by the U.S. Department of Energy.