Abandoned oil wells 'super-emitters' of greenhouse gas methane

Abandoned oil and natural gas wells may be a substantial source of the greenhouse gas methane to the Earth's atmosphere, according to a new US study.
Princeton University researchers tested a sample of abandoned oil and natural gas wells in northwestern Pennsylvania and found that many of the old wells leaked substantial quantities of methane.
Since there are so many abandoned wells in the US (a recent study from Stanford University concluded there were roughly 3 million abandoned wells in the country) the overall contribution of leaking wells could be significant, researchers believe.
"The research indicates that this is a source of methane that should not be ignored," said Michael Celia, the Theodore Shelton Pitney Professor of Environmental Studies and professor of civil and environmental engineering at Princeton.

While oil and gas companies work to minimise the amount of methane emitted by their operations, almost no attention has been paid to wells that were drilled decades ago.
Mary Kang, then a doctoral candidate in civil and environmental engineering at Princeton, and colleagues chose 19 wells in the McKean and Potter counties in northwestern Pennsylvania.

The wells chosen were all abandoned, and records about the origin of the wells and their conditions did not exist.
Only one of the wells was on the state's list of abandoned wells. Some of the wells, which can look like a pipe emerging from the ground, are located in forests and others in people's yards.

Kang, now a postdoctoral researcher at Stanford, said the lack of documentation made it hard to tell when the wells were originally drilled or whether any attempt had been made to plug them.
"What surprised me was that every well we measured had some methane coming out," added Celia.
Although all the wells registered some level of methane, about 15 per cent emitted the gas at a markedly higher level - thousands of times greater than the lower-level wells.
Denise Mauzerall, a Princeton professor and a member of the research team, said the relatively low number of high-emitting wells could offer a workable solution: while trying to plug every abandoned well in the country might be too costly to be realistic, dealing with the smaller number of high emitters could be possible.

The researchers estimate that emissions from abandoned wells represents as much as 10 per cent of methane from human activities in Pennsylvania - about the same amount as caused by current oil and gas production.
Also, unlike working wells, which have productive lifetimes of 10 to 15 years, abandoned wells can continue to leak methane for decades, researchers said.