🫧 Unused oil and gas wells emit 1000 times more microbial methane than estimated

Microbial methane is escaping from oil and gas wells that are no longer in use at rates approximately 1,000 times higher than previous estimates.

"Methane is a potent greenhouse gas when released into the atmosphere, regardless of its source. Specifically, this study suggests that unused oil and gas wells could continue to emit microbial methane long after the targeted formation has been completely depleted," explains Mary Kang, co-author of the study and an associate professor of civil engineering.

"That said, it is often difficult to determine exactly where this methane is coming from, because the subsurface is a complex system with multiple gas formations," she adds.


Not only did the team find microbial methane in 23% of the unused wells sampled—about three times more than previous estimates—but they also detected traces of microbial methane in 50% of the unused wells.

Canada has nearly 500,000 unused oil and gas wells. Not all of them emit methane, of course, but the study cites previous research by the same team revealing that the top 12% of wells emitting the highest quantities were responsible for 98% of the emissions from this source. According to scientists, it is essential to understand the origin and nature of these emissions in order to manage them effectively.

Leaks primarily from underground depths The team collected samples from 401 unused wells across the country, particularly in Western Canada, where over 90% of these wells are located. "Unused wells" included inactive wells, those that had never been productive, and those whose production had ceased.

"We examined chemical properties, such as gas composition and stable isotopic signatures, which provide better insight into the origins of methane leaks. This analysis is very sensitive, and we were able to reliably characterize the origins of emissions from 100 of the 401 sampled wells," says Gianni Micucci, co-author of the study and a postdoctoral researcher in civil engineering.

The team demonstrated that most methane leaks came from "thermogenic" sources, which are typically found in deep oil formations where organic matter from ancient lifeforms "cooks" at high temperatures. But in previous research, the contribution of microbial methane, typically found in shallow formations, appears to have been underestimated.

Emission pathways difficult to trace The researchers stated that their observations raised new questions about the movement of methane underground and its leakage through wells.

"In light of our results, we wonder if the studied wells were located above formations containing microbial methane and if they constituted an exit pathway to the atmosphere for this type of methane," explains Gianni Micucci.

Mary Kang hopes that this study will lead to a better understanding of the "complex nature of the subsurface" and improve ongoing efforts to reduce emissions on oil and gas sites.

The Study The article "Origins of Subsurface Methane Leaking from Nonproducing Oil and Gas Wells in Canada," by Gianni Micucci and Mary Kang, was published in the journal Environmental Science and Technology.