Natural soils-based oxidation mitigates methane leakage from integrity compromised legacy wells

An increasing number of legacy petroleum wells are reported to suffer integrity failure, releasing methane (CH4) into the subsurface and atmosphere. Subsurface released methane is reactively transported toward ground surface with a portion converted to carbon dioxide by soil microbes. Currently, the extent to which fugitive CH4 oxidation occurs, including microbial taxa responsible and controlling parameters are poorly understood. Here, we examined fugitive CH4 leakage at a legacy well in the Montney region of British Columbia, Canada and find up to 90% is oxidized at rates as high as 230 g of CH4/m2 of soils/day during summer. Meanwhile, a profound difference in microbiome between soils at the wellhead and background was observed, while modeling suggests that prevailing seasonal temperature will moderate CH4 oxidation extent. Overall, we find that filtration of fugitive CH4 through natural soils can significantly reduce emissions of CH4 and mitigate climate impacts from such sources.