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  • Gasfields Commission
  • 2017-11-14

A Natural Solution to a Bored Problem?

Scientists at the University of Queensland believe they may have found a natural solution to the modern challenge of decommissioning old wells.

Led by Professor Brian Towler - who hails from Chinchilla - researchers are trialing the use of locally sourced bentonite clay formed into specialised plugs in place of cement.

Bentonite clay is already used to line dams and water storages and the principles apply to plugging wells.

The real advantage is that when they are hydrated they should be self-healing.

Once installed the plugs would be immune to seismic events, contortion and potentially even to corrosion of the well casing and may yet prove less expensive and easier to use than current methods.

To plug the wells, the bentonite is formed into cylindrical plugs a bit like an artillery shell in shape.

These plugs are then lowered or dropped down the well to cover over any exposed aquifers and then topped up with water.

The clay hydrates and expands, sealing the well by swelling out against the sides and remains in place indefinitely.

Bentonite is a stable geological material that has existed in the earth for millions of years.

Field trials began in July 2016 on a water bore near Chinchilla and the effectiveness of the plug has been repeatedly tested to a pressure of 500 psi.

The University of Queensland has also commissioned a well simulator facility to test the plugs at extreme pressures under laboratory conditions and is working with the Queensland regulator to ensure all tests and trials are in place and validated before full deployment.

Director of the UQ Centre for Coal Seam Gas, Professor Andrew Garnett, says the bentonite project may become a big step forward to developing new and innovative technologies with potentially better environmental performance than existing solutions.

Professor Garnett says, “we’re really excited by this project and its potential to support the bentonite industry in regional areas as the gas industry moves into more of a long term, maintenance phase”.

There are extensive deposits of bentonite in Queensland and the solution could help secure local employment to mine the bentonite as well as manufacture and insert the plugs.

Chief Executive Officer of the GasFields Commission, Carolyn Collins says, “the science surrounding the gas industry, water aquifers and beneficial use of both resources is growing all the time”.

Ms Collins says, “the use of bentonite plugs seems like such a simple solution when you first see it in action and the science that has gone into the idea is really quite amazing”.

There are thousands of CSG wells still to be drilled in Queensland and hundreds of thousands of old coal and water bores in existence that will need to be plugged and decommissioned in the future.

For more information on the bentonite plug trials, visit the UQ Centre for Coal Seam Gas website.