Introduction The recent Intergovernmental Panel on Climate Change (IPCC) special report on global warming of 1.5°C highlighted the importance of reducing short-lived greenhouse gases like methane (Intergovernmental Panel on Climate Change, 2018). Methane, a major component of natural gas, has a global warming potential that is 36 times that of carbon dioxide over a 100-year period (Myhre, et al., 2013), and even higher over shorter time periods (Etminan, Myhre, Highwood, & Shine, 2016). Furthermore, methane emissions contribute to sea-level rise over much longer timescales than their atmospheric lifetimes (Zickfeld, Solomon, & Gilford, 2017). These consequences are troubling given that official methane emissions inventory in the US and Canada have been found to be systematically underestimated (Alvarez, et al.,

Reducing methane emissions from the oil and gas industry is a critical climate action policy tool in Canada and the US. Optical gas imaging-based leak detection and repair (LDAR) surveys are commonly used to address fugitive methane emissions or leaks. Despite widespread use, there is little empirical measurement of the effectiveness of LDAR programs at reducing long-term leakage, especially over the scale of months to years. In this study, we measure the effectiveness of LDAR surveys by quantifying emissions at 36 unconventional liquids-rich natural gas facilities in Alberta, Canada. A representative subset of these 36 facilities were visited twice by the same detection team: an initial survey and a post-repair re-survey occurring ∼0.5-2 years after the initial survey. Overall, total emissions reduced by 44% after one LDAR survey, combining a reduction in fugitive emissions of 22% and vented emissions by 47%. Furthermore, >90% of the leaks found in the initial survey were not emitting in the re-survey, suggesting high repair effectiveness. However, fugitive emissions reduced by only 22% because of new leaks that occurred between the surveys. This indicates a need for frequent, effective, and low-cost LDAR surveys to target new leaks. The large reduction in vent emissions is associated with potentially stochastic changes to tank-related emissions, which contributed ∼45% of all emissions. Our data suggest a key role for tank-specific abatement strategies as an effective way to reduce oil and gas methane emissions. Finally, mitigation policies will also benefit from more definitive classification of leaks and vents.

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