Old oil and gas wells are releasing more methane than previously thought

A new study by McGill University in Canada has revealed that old, non-producing oil and gas wells may be leaking significantly more methane into the environment than official figures suggest.

Researchers collected data from 494 non-producing wells across five Canadian provinces, building the largest national database of its kind. Their findings estimate that these wells release around 230 kilotonnes of methane annually, about seven times higher than the 34 kilotonnes currently reported in Canada’s official National Inventory Report.

Canada has more than 400,000 non-producing oil and gas wells, many of which were drilled years or even decades ago and are now either sealed (plugged) or abandoned (unplugged). Similar situations exist worldwide, including more than 3 million such wells in the United States.

Mary Kang, Associate Professor of Civil Engineering at McGill and senior author on the paper said: ‘Non-producing wells are one of the most uncertain sources of methane emissions in Canada. We measured the highest methane emission rate from a non-producing oil and gas well ever reported in Canada.’

The study also found that just a small number of wells are responsible for most of the methane emissions. However, identifying these high-emitting wells has been difficult, partly because different studies have produced conflicting results about which well characteristics (such as location, age, depth, or type) are most closely linked to high emissions.

Kang added: ‘One surprising finding was just how much the drivers of emissions varied between provinces. We thought geological differences within provinces would matter more, but the dominant factors appear to be at the provincial scale, likely due to variations in policy and operational practices.

By separating emissions from the wellhead (above-ground equipment) and the surface casing vent (a pipe used to relieve underground pressure), the researchers gained more precise insights into where leaks are coming from. They found that certain factors, such as whether a well is plugged and its geographic location, are consistently linked to higher emissions.

Kang said: ‘Rather than just measuring more wells at random, we can use well attributes to identify where emissions are likely to be highest, and focus monitoring and mitigation efforts there. If we don’t have accurate estimates of methane emissions, we can’t design effective climate policies.’