Mary Kang and Gianni V. R. Micucci
Photo Credit: Mary Kang
Scientific Frontline: Extended "At a Glance" Summary: Microbial Methane Emissions from Non-Producing Wells
The Core Concept: Non-producing oil and gas wells emit microbial methane—a potent greenhouse gas—at rates approximately 1,000 times higher than previously estimated, acting as a continued source of atmospheric emissions long after a well has ceased production.
Key Distinction/Mechanism: While traditional models assume most methane leaks derive from deep, high-temperature "thermogenic" sources (where ancient organic matter is "cooked"), this research reveals a drastically underestimated contribution from "microbial" methane originating in shallower subsurface formations. Non-producing well structures can inadvertently serve as migration pathways, allowing this shallow microbial methane to escape into the atmosphere.
Major Frameworks/Components:
- Isotopic Signature Analysis: Utilization of stable isotopic signatures and gas composition analysis to accurately trace the origin (microbial vs. thermogenic) of leaking methane.
- Subsurface Migration Pathways: The theoretical framework investigating how multiple gas-bearing formations interact with inactive well infrastructure to route shallow gases to the surface.
- Emission Asymmetry: The statistical observation that a small minority of wells (the top 12 percent) are responsible for the vast majority (98 percent) of the total methane emissions from these sources.
Branch of Science: Environmental Science, Geochemistry, Earth Sciences, and Civil Engineering.
Future Application: The precise identification of microbial methane sources will inform the design of targeted plugging and abandonment protocols for the millions of non-producing wells globally. By understanding specific subsurface migration pathways, engineers can develop improved mitigation technologies to permanently seal high-emitting wells.
Why It Matters: Methane is a highly potent greenhouse gas that significantly drives near-term climate change. Recognizing that non-producing wells continue to emit substantial volumes of microbial methane—and identifying exactly where that methane originates—is a critical step toward managing global greenhouse gas inventories and deploying effective, targeted climate mitigation strategies.
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 McGill University researchers.
“Methane is a powerful greenhouse gas when released into the atmosphere, regardless of its origin. 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,” said Mary Kang, co-author and Associate Professor of Civil Engineering.
“However, the exact source of this methane is often unclear because the subsurface is a complex system with multiple gas-bearing formations,” she said.
The team not only found microbial methane at 23 percent of the non-producing wells sampled – roughly three times higher than earlier estimates – but also detected traces of microbial methane in another 50 percent 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 percent of emitting wells account for 98 percent 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 percent of these wells are located. “Non-producing wells” included inactive wells, those that have never produced and those that have ceased production.
“For this study, we 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,” said Gianni Micucci, study co-author and Postdoctoral Researcher in Civil Engineering.
The researchers showed that most methane leaks typically derive from “thermogenic” sources – usually found in petroleum formations deep below ground, where organic matter derived from ancient life “cooks” under high 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.
“Our results raise the question of whether the studied wells were above microbial methane-containing formations, and whether they provide a pathway for this microbial methane to migrate into the atmosphere,” Micucci explained.
Kang said she hopes the study provides insights into the “complex nature of the subsurface” and improves ongoing efforts toward mitigating emissions at oil and gas sites.
Funding: The research was funded by the Natural Sciences and Engineering Research Council of Canada.
Published in journal: Environmental Science and Technology
Title: Origins of Subsurface Methane Leaking from Nonproducing Oil and Gas Wells in Canada
Authors: Gianni V. R. Micucci, and Mary Kang
Source/Credit: McGill University
Reference Number: env040926_03
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