Soil plays crucial role in breaking down methane from leaking legacy wells

New research has revealed that soils surrounding onshore oil and gas wells are able to absorb methane leakage, preventing the potent greenhouse gas from entering the atmosphere and contributing to global warming.

The study, led by researchers from the Lyell Centre, Heriot-Watt University’s Global Research Institute for earth and marine sciences, investigated a leaking decommissioned petroleum well in British Columbia, Canada, and found that up to 90% of the escaped methane from the leaking well is oxidised by microbes in the soil, converting it to less harmful carbon dioxide. Methane is 28 times as potent as carbon dioxide at trapping heat in the atmosphere so this conversion is massively beneficial.

The study also highlighted that striking seasonal variations in the rate of methane breakdown are likely to occur, with the summer providing the optimal conditions for the soil to filter methane. Here, modelling suggests that methane emissions can be up to ten times higher in the winter, bringing the annual average level of methane breakdown to 40%.

Key species of bacteria within the soil, including species from the genera Methylocystis and Methylocella, which are considered some of the most abundant in soil, were also found to be crucial to the natural methane filtration process.

The findings highlight the significant role that natural soils can play in mitigating methane leakage and could lead to development of strategies for enhancing this natural process to further reduce greenhouse gas emissions.

Dr Aaron Cahill, Assistant Professor of Applied Geoscience and Environmental Risk at The Lyell Centre, led the study.

He said: “Unfortunately, more and more legacy oil and gas wells are being identified with a failed structure and are leaking methane into the environment. Up to now, no one has robustly determined how much methane is potentially being broken down after release or which microbes are doing the job.

“This study of a leaking well in Canada has provided vital data into the effectiveness of soil microbes which, in the summer, can convert nearly all the escaped methane to less harmful carbon dioxide. Our calculations, alongside a better understanding of the various bacteria involved in the consumption process, gives us the knowledge to potentially enhance efforts to reduce the climate impact of leakage from legacy oil and gas wells by harnessing this natural process.”

A paper outlining the findings, Natural soils-based oxidation mitigates methane leakage from integrity compromised legacy wells (Cahill, A. G., McClure, J., & de Jonge-Anderson, I.) was published in Geophysical Research Letters on 28 February.