Woodside used Seatrac, the Perth-based subsea service provider, and the company's proprietary underwater jet-cutting system, dubbed Axe, in conjunction with an ROV spread and a utility work vessel. No explosives were used when abandoning the multi-casing subsea exploration wellheads, Wamac-1, Wamac-1a and Nelson Rocks, as well as the cleaning and inspection of Madelaine-1, one of the North West Shelf's early wells.
An official at the state's Minerals and Petroleum Department is reported to have said what Seatrac had achieved was "technically far superior to what has been achieved in the North Sea and GoM".
A previous attempt in Western Australia by a European contractor using a civil construction cutting tool failed to remove the wellheads with the result that they had to be blown off using explosives.
Seatrac marketing director Simon Ashton said: "It's been a long hard road over the past three years, and there have been many times when it appeared that the technical challenges were all but insurmountable. However, the project has been a great success."
Woodside drilling manager Kevin Gallagher said: "The fundamental step changes in the cost and reduction in environmental impact of subsea wellhead removal is fully aligned with Woodside's operating philosophy and we are delighted to have been the first company to use Seatrac's system in the field."
Seatrac's technology requires only medium pressures of between 10,000 and15,000 psi. The key to a successful jet-cutting system lies in the grit formula and the grit-to-water ratio, both of which are trade secrets.
In addition, Seatrac uses "the same hose to deliver the grit and water to the cutting nozzle, ensuring consistent and repeatable performance", said Ashton.
Ashton estimates there are about 240 wellheads off Western Australia alone that require abandonment.