New use for clay could prevent water contamination from CSG wells

Posted 22 March 2017

CSG wellsPreventing water contamination from decommissioned oil and gas wells could soon be cheaper and safer thanks to new material trials from the University of Queensland. 

Decommissioned wells are commonly sealed with a series of cement plugs that aim to prevent any cross-flow of water and gas. 

But the University of Queensland's Centre for Coal Seam Gas and the School of Chemical Engineering are instead championing the use of bentonite in a recent paper

Co-author Professor Brian Towler said there were a number of benefits.

“Bentonite is not only cheap, but also easier to handle. Once bentonite is hydrated, it creates a potentially more reliable plug that is flexible and self-healing,” he said.

“The number of CSG wells in Queensland has skyrocketed in the past decade and there are still many more planned.

“Over the next few decades, tens of thousands of holes will eventually need to be plugged.”

Towler explained that in order to plug the wells, dry clay was compressed into a cylindrical shape, then dropped or lowered down the hole.

The hole was then filled up with water, causing the clay to swell against the sides of the column and seal it off indefinitely. 

Compared to concrete, bentonite also had the advantages of being malleable, self-healing and widely available in Queensland.

“This could mean local jobs for regional Queensland, not only in mining bentonite, but also manufacturing and inserting the plugs,” Towler said. 

In another recent development in the field, CSIRO research found water produced during coal seam gas extraction could be safely re-injected into aquifers if it was appropriately pre-treated.