Methane migration is the term used to describe the movement of methane gas from deep underground up to the surface. Methane drifts upwards to the surface over geologic time, but drilling can speed up the process. Because methane under high pressure naturally migrates to areas of lower pressure, drilling can cause gas pockets that have been stable for thousands of years to move. Shale gas is trapped in porous rock formations and drilling through these formations creates a conduit for the gas to escape.
The industry disputes that fracking causes methane migration and points the finger at faulty drilling and well casings as the likely cause. Fracturing the rocks deep underground may not be the primary cause of methane migrating into rivers and domestic water supplies - but as drilling and well casing are an intrinsic part of the fracking process, isn't this just hair splitting?
Well Integrity, Not Fracking
The position that sub-standard drilling or poor well casing, not fracking, is the cause of methane migration, looks a lot like smoke and mirrors to affected water users. With no fracking for gas there wouldn't be a need to drill or case wells with steel and cement that can, and does, fail. In the end, whether it's fracking or elements of the fracking process that causes methane to migrate, the result is the same for people whose water is impacted.
Farmers on the Darling Downs in Queensland say they've known for decades that some of their bores have traces of methane, but the methane bubbling up to the surface in the Condamine River near Chinchilla's gasfields is a new phenomenon. The company, Origin Energy, says it's confident the seepage isn't a result of their exploratory well drilling.
Orphaned and abandoned oil and gas wells create a natural pathway for methane to migrate from. Methane migration can be accelerated when a new well is drilled into the same formation that an abandoned well is already tapped into. While rare, this occurrence, called 'communication', can create major problems at the surface. Drilling near an abandoned well in the Marcellus Shale is the prime suspect in the spectacular 10 metre geyser of gas and water that burst through the ground in Tioga County, Pennsylvania in 2012.