A small number of wells produce large emissions

Focus on the Environment

By Molly Seltzer

Wells that extract natural gas from underground often leak large amounts of methane, a powerful greenhouse gas, into the air. A team of Princeton researchers has found that, in one of the biggest gas-producing regions, most of these emissions come from a tiny subset of the wells, a finding with major implications for how to control the problem.

Researchers led by Mark Zondlo, an associate professor of civil and environmental engineering, spent two years sampling emissions from the Marcellus Shale, a basin that stretches from West Virginia to Pennsylvania to New York State. In research published in the journal Environmental Science and Technology in March 2019, the authors reported that 10% of wells account for more than three-quarters of gas leaked into the atmosphere as a byproduct of extraction. That has the equivalent greenhouse gas effect of adding 500,000 cars, or about 2% of the U.S. auto market, to the road.

This finding, however, may have a silver lining for mitigating impacts on the environment, Zondlo said, because fixing a relatively small number of these “superemitting” wells could lead to a major reduction in emissions. He cautioned that identifying the leakiest wells is not always easy, in part because well emissions can change over time.

The researchers said the emissions can result from a variety of practices, including the intentional opening of valves to relieve pres-sure at wells, or from valves that are unintentionally stuck open. Previous studies have looked at small samples of wells in Texas and West Virginia and reached similar conclusions about the impact of “superemitters.” The new research is the first to look at operations over the most productive shale basin in the U.S. and represents the largest total number of wells measured.

David Lyon, a scientist at Environmental Defense Fund who has worked on previous methane emissions assessments, said: “The results from this study reinforce the urgent need to reduce methane leaks from Pennsylvania’s existing unconventional gas wells. These leaks represent $70 million in wasted natural gas resources and have a short-term climate impact equivalent to that of nine coal-fired power plants.”

Along with Zondlo, principal researchers on the team included Elie Bou-Zeid, professor of civil and environmental engineering, and Jeffrey Fitts, a former research scholar. All three were affiliated with Princeton’s Andlinger Center for Energy and the Environment. Dana Caulton, a former postdoctoral researcher in Zondlo’s lab, led the field sampling. Support for the research was provided in part by the National Oceanic and Atmospheric Administration.