Researchers from the University of Queensland have developed a new solution for plugging decommissioned oil and gas wells, with the possibility of making the process safer and more economical.
The solution was developed by Professor Brian Towler's team from the University of Queensland Centre for Coal Seam Gas and School of Chemical Engineering, and it involves using bentonite, a naturally-occuring clay, to manufacture plugs for the oil and gas wells.
"Bentonite is not only cheap, but also easier to handle," Professor Towler said.
"Once bentonite is hydrated it creates a potentially more reliable plug that is flexible and self-healing."
This more reliable solution comes at a good time, as there is a growing number of coal seam gas wells in Australia, and there are many more still planned.
"Over the next few decades tens-of-thousands of holes will eventually need to be plugged," Professor Towler explained.
When a well is no longer used for coal seam gas operations, it is abandoned. This process involves sealing the well with a series of cement plugs to prevent the intermixing of fluids and pressures between aquifers, to prevent the escape of fluids and emissions from the well to the surface, and to prevent injury and pollution.
Currently, coal seam gas wells are sealed with cement plugs that must be pressure tested. The use of cement as the primary plug material is a mandatory requirement according to the Queensland Department of Natural Resources of Mines Code of Practice.
According to Professor Towler, bentonite plugs could be superior to cement plugs due to their malleable, self-healing characteristics. The clay is also cost-effective, with extensive deposits available in Queensland.
"This could mean local jobs for regional Queensland, not only in mining bentonite, but also manufacturing and inserting the plugs," he said.
To plug wells with bentonite, the dry clay is compressed into a cylindrical shape, then dropped or lowered down the vertical CSG hole or water well, usually into a standing water column.
The hole is then filled up with water and the clay is allowed to hydrate, causing it to seal the hole by swelling out against the sides.
The bentonite plug remains in place, sealing the hole indefinitely.
The development of the cost-effective plugging technology was funded by a $175,000 Advance Queensland Grant, and supported via a partnership with Shell (formerly QGC), Santos, Arrow Energy and Australia Pacific LNG through the Centre for Coal Seam Gas.