Canada is home to more than 400,000 nonproducing oil and gas wells. These abandoned facilities still emit methane, which can contaminate water supplies and pollute the atmosphere with a greenhouse gas more potent than carbon dioxide. The scope of these emissions may be greater than previously understood, according to a new study.

In 2023, nonproducing wells may have leaked 230 kilotons of methane, about 7 times more than the official estimates published in the government’s annual National Inventory Report (NIR). The NIR, compiled by Environment and Climate Change Canada (ECCC), informs the country’s greenhouse gas mitigation efforts and is submitted as part of Canada’s reporting obligations to the United Nations Framework Convention on Climate Change.

Methane estimates are calculated by multiplying the total number of nonproducing wells by emissions factors determined by well characteristics, such as the type of well (oil, gas, or unknown), depth, and whether it is plugged with concrete. These emissions factors offer only a rough idea of methane leakage, however.

“It’s really hard to predict emissions,” said Mary Kang, a study coauthor and associate professor of civil engineering at McGill University in Montreal. “There’s a range of engineering, geological, and policy-related factors that are all playing a role in what emissions rates are observed.”

Surprising Discoveries

To address this ambiguity, Kang and her colleagues measured methane flow rates at 494 nonproducing wells throughout Canada between 2018 and 2023 to define new emissions factors. While these sites account for only a fraction of the country’s abandoned wells, making uncertainty inevitable, the authors describe their data as the largest set of direct methane emissions figures collected through consistent methods.

They reported that the amount of methane leaked from the nonproducing wells was 1.5–16 times greater than NIR estimates.

Most of the departure from the NIR figures was driven by leaks from surface casing vents, narrow slits that ring the outermost steel layer surrounding the wellbore itself. Kang explained that emissions from surface casing vents indicate issues with a mine’s structural integrity and are trickier to manage than wellhead leaks, which may require only minor adjustments at the surface.

The researchers analyzed their measurements to gauge how different well attributes contribute to methane flow rates. Whether a well is more prone to leakage than others, they found, isn’t determined by a single emissions factor such as its age or operating company.

Still, Kang was surprised to discover how much flow rates varied by province, even between wells operated by the same company in similar locations. The highest rates were observed in Alberta, where 74% of Canada’s known nonproducing wells are located.

“The geology doesn’t care if you’re in one province or another,” she said. “It’s the same formation. So what’s going on?”

Kang noted that each province and territory has its own emissions regulations, and policy factors might explain the differences in methane flow rates, though other geological differences such as seismic activity could also be at play.

Continuous Improvement

Complicating any study of methane emissions from nonproducing wells is the large number of sites abandoned before contemporary recordkeeping practices were established, said Maurice Dusseault, professor emeritus of engineering geology at the University of Waterloo in Ontario, who was not involved in the research.

A history of well abandonment practices in Ontario illustrates how hard it is to identify older wells throughout Canada. The first oil well in Ontario was drilled in 1858, but records were not mandatory in the province for another 60 years. Surface casings were often removed when a well closed so that the steel could be reused in other mines. This means some legacy wells cannot be detected with conventional magnetic techniques.

Still, Dusseault praised the researchers for their rigorous pursuit of better emissions estimates.

Kang and her colleagues returned to the field this year and last year, measuring methane flow at additional known well sites and revisiting previous sites to observe how leakage changes over time.

Meanwhile, their work is already affecting how the country approaches methane emissions. “Continuous improvement is a key principle of Canada’s NIR,” wrote ECCC spokesperson Cecelia Parsons in an email, noting that the improvement plan in the 2025 NIR draws from the new research.

This article originally appeared in EOS Magazine and was republished under a CC BY-NC-ND 3.0 license.