Non-producing oil and gas wells emit microbial methane at rates 1,000 times higher than previously estimated
Microbial methane leaking from non-producing oil and gas wells is being emitted at rates about 1,000 times higher than previously estimated, according to a new study led by 海角社区 researchers.
鈥淢ethane is a powerful greenhouse gas when released into the atmosphere, regardless of its origin. In particular, this study implies that non-producing oil and gas wells could continue to emit microbial methane long after the targeted formation has been fully depleted,鈥� said Mary Kang, study co-author and Associate Professor of Civil Engineering.
鈥淗owever, the exact source of this methane is often unclear because the subsurface is a complex system with multiple gas-bearing formations,鈥� she said.
The team not only found microbial methane at 23 per cent of the non-producing wells sampled 鈥� roughly three times higher than earlier estimates 鈥� but also detected traces of microbial methane in another 50 per cent of them.
Canada has nearly 500,000 non-producing oil and gas wells. While not all leak methane, the study noted previous research by the same team that found the top 12 per cent of emitting wells account for 98 per cent of emissions from this source. Understanding where these emissions come from and their nature is key to managing them effectively, the researchers said.
Most methane leaks originate deep underground
The team collected samples from 401 non-producing wells across the country, particularly in Western Canada where more than 90 per cent of these wells are located. 鈥淣on-producing wells鈥� included inactive wells, those that have never produced and those that have ceased production.
鈥淔or this鈥� study, we鈥� looked at chemical properties such as gas composition and stable isotopic signatures, which enable a better understanding of the origins of the leaking methane. This analysis is highly sensitive, and we were able to reliably characterize the origins of emissions from 100 of the 401 wells sampled,鈥� said , study co-author and Postdoctoral Researcher in Civil Engineering.
The researchers showed that most methane leaks typically derive from 鈥渢hermogenic鈥� sources 鈥� usually found in petroleum formations deep below ground, where organic matter derived from ancient life 鈥渃ooks鈥� under鈥痟igh temperatures. But previous research appears to have underestimated the contribution of microbial methane, which is typically found in shallow formations.
Emissions pathways still unclear
The researchers said the findings raise new questions about how methane moves underground and escapes through wells.
鈥淥ur results raise the question of whether the studied wells were above microbial methane-containing鈥痜ormations, and whether they provide a pathway for this microbial methane to migrate into the atmosphere,鈥� Micucci explained.
Kang said she hopes the study provides insights into the 鈥渃omplex nature of the subsurface鈥� and improves ongoing efforts toward mitigating emissions at oil and gas sites.
About the study
鈥�,鈥� by Gianni Micucci and Mary Kang, was published in Environmental Science and Technology.
The research was funded by the Natural Sciences and Engineering Research Council of Canada.
