When wells are decommissioned, cement plugs are installed and well casings are cut a couple of metres below the ground, but this does not stop buoyant methane gas from gradually working its way to the surface, both from within and outside the casing. 

JEFF MCINTOSH/THE CANADIAN PRESS 

Richard Jackson is a fellow at Geofirma Engineering and an adjunct professor at the University of Waterloo. Maurice Dusseault is a professor of geological engineering at the University of Waterloo. Christopher Holly…