Speaking at the APPEA National Conference on the Gold Coast yesterday, Williamson said fishing trawlers in the area had damaged one of the development’s three subsea wells, Blackback A1A. As a result, the well started leaking natural gas at unreasonably high rates, he said.
Traditionally, a floating drill rig would have been mobilised to permanently shut down the well, as low production rates did not justify using a work-over rig to repair the damage, he said.
A team led by Williamson recently finished trialling a new technique that involves pumping “kill fluids” down the well via a 23km gas-lift pipeline from the Mackerel host platform.
“It was critical there would be no impact on the other wells and we pre-identified several big operational risks,” he said.
These included the potential for hydrate to form in the pipelines, over-pressure or blockage of the gas-lift pipeline and dangers arising from using large volumes of methanol in the process.
However, Williamson said the operation went according to plan, with no safety or environmental problems.
“The A1A well has now been killed for eight months, while the other wells have been restarted and returned to full production,” he said.
“Our technique has been proven as an innovative method for securing subsea wells, as well as providing significant cost efficiencies when compared with the alternative – the mobilisation of a floating drill rig.”
Seven years ago, Esso and BHP Billiton developed the Blackback field in the Gippsland Basin, which was discovered in 1975. It is 87km offshore and in 400m of water.
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