New field evidence from Canada shows old wells can leave a hidden leakage footprint
Old oil and gas wells may continue to affect the environment long after they have stopped producing, with new field evidence showing that their leakage footprint can be broader and more persistent than surface methane measurements alone reveal.
A study led by researchers at The Lyell Centre, Heriot-Watt University, examined persistent methane leakage from a legacy petroleum well in British Columbia, Canada. The team found that while methane emissions at the ground surface were concentrated in a relatively small area and varied through time, the leakage also left a wider detectable signature in the shallow subsurface and surrounding soils.
The findings are particularly relevant for Canada, where there is a very large population of non-producing, inactive, abandoned and orphaned oil and gas wells. Many legacy wells are assessed using surface measurements, but the new study suggests that surface methane monitoring alone may miss part of the leakage picture.
Published in Geophysical Research Letters, the study combined repeated methane and carbon dioxide surface flux surveys with shallow geophysical measurements and soil geochemical analysis. Together, these methods showed that persistent leakage was expressed not only as a compact surface emission zone, but also as a broader subsurface electrical anomaly and a wider soil geochemical footprint.
The work provides what the authors believe is the first direct field evidence that persistent methane leakage from a legacy petroleum well can leave a nested environmental footprint across multiple measurement domains. This helps explain why methane leakage from older wells can be difficult to detect and interpret using surface measurements alone.
Dr Aaron Cahill, Associate Professor of Applied Geoscience and Environmental Risk at Heriot-Watt University, said: “Old wells do not always tell a simple story at the surface. Methane emissions can be patchy, variable and partly modified by soil processes, but persistent leakage can still leave a broader environmental signature below ground and in soil chemistry.
“That is the key finding here. If we only look for methane at the surface, we may miss part of the leakage picture. By combining surface, subsurface and soil measurements, we get a much clearer view of what is happening around these legacy wells.”
Legacy oil and gas wells are increasingly recognised as a source of methane emissions and environmental liability. The study suggests that combining complementary field
measurements could help regulators and industry more confidently identify and characterise wells that continue to pose environmental risks.
The findings may also have wider relevance for carbon capture and storage, where confidence in detecting and interpreting possible leakage pathways is important for long-term containment assurance.
The paper, A Multi-Scale Geophysical-Geochemical Footprint of Persistent Methane Leakage at a Legacy Petroleum Well, is published in Geophysical Research Letters.
Journal
Geophysical Research Letters
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
New field evidence from Canada shows old wells can leave a hidden leakage footprint
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