Major oil spill off Australia’s coast would dwarf Deepwater Horizon disaster, documents show

A worst-case oil spill in the Great Australian Bight would be twice the scale of the Gulf of Mexico disaster, and rough seas and a lack of suitable equipment risk delaying the response effort, confidential plans show.

Documents released under freedom of information laws reveal the potential dangers involved in drilling for oil in the wild, isolated seas off the South Australian coast – a move Resources Minister Matt Canavan last week said was a “national priority” that would secure Australia’s fuel supplies.

Norwegian energy giant Equinor plans to explore for oil in the Great Australian Bight and insists it can be done safely. Critics say the venture is too risky and an oil spill in the pristine region would damage coastal communities and devastate marine life, including endangered southern right whales.

Equinor last year acquired two exploration permits from BP, and plans to drill an exploratory well by October next year.

A plan for the well prepared by BP outlines how it would respond in the event of a blowout – an accidental, uncontrolled release of crude oil. The document was obtained by Greenpeace after a two-year freedom-of-information battle with the National Offshore Petroleum Safety and Environmental Management Authority.

It shows that in the worst-case discharge event, 7.9 million barrels of oil would spill into the ocean over 149 days – the time needed to drill a relief well to stop the flow.

In 2010, BP’s Deepwater Horizon spill discharged 4 million barrels of oil into the Gulf of Mexico, of which just 810,000 was collected. It was the largest marine oil spill in history.

BP said a spill in the bight might also be tackled by using a chemical dispersant to break up the oil. Such an intervention should be made within 10 days, but this may not occur due to weather and ocean conditions, it said. Research has also suggested dispersants were ineffective in the Deepwater Horizon disaster.

BP also proposed placing a cap on the damaged well using equipment located in Singapore. This would take more than three weeks to deliver and deploy, and may be delayed by a lack of available vessels or rough seas.

The plan, which was approved by the petroleum safety authority, said there was “significant uncertainty” in predicted temperatures and fluids BP would encounter when drilling.

As Fairfax Media reported in April, BP had also attempted to support its drilling plans by claiming an oil spill would benefit nearby coastal towns because the clean up would boost their economies.

Equinor, which recently changed its name from Statoil, will prepare its own plan to manage the well operations. In a statement to Fairfax Media, the company did not say how its plan would differ to that proposed by BP.

Equinor is also developing an environment plan, which the company says will only be accepted if it “can demonstrate that the environmental risks and impacts have been reduced to a level that is ‘as low as reasonably practicable’ and acceptable”.

Equinor had conducted extensive baseline surveys and determined the project was “well within the range where we’ve safely operated before … we only undertake activities if they can be done safely”.

Greenpeace Australia senior campaigner Nathaniel Pelle said BP’s plans showed the massive challenges involved in drilling in the bight.

“No oil company knows what to expect in terms of pressures and temperatures beneath the sea bed … which makes the risk of an accident exceptional when compared to drilling in existing oil provinces,” he said.

“Not only is there a greater than normal risk of an accident, but … responding to it would be incredibly difficult and probably impossible before severe damage is already done.”

The Morrison government is trying to attract international investors to the Equinor project.

Senator Canavan told Fairfax Media that secure oil and gas supplies “are critical to Australia’s ongoing energy security and to protect manufacturing jobs around the nation”.

“Offshore petroleum exploration activities have occurred safely in Australian waters since the late 1960s,” he said.

But independent South Australian senator Tim Storer said the risks of drilling in the bight “simply don’t justify the rewards”.

He plans to move amendments to federal environment laws that would hand responsibility for assessing such proposals to Environment Minister Melissa Price, to “provide for a more rigorous assessment”.

“Talking to local government, local business, community groups and representatives from the eco-tourism industry, I heard first-hand the devastating impacts a spill would have on regions such as Kangaroo Island and Port Lincoln,” he said.

A spokeswoman for the offshore petroleum safety authority said it would not approve a drilling project unless the proponent addressed risks involved in the conditions, water depth and remoteness of the proposed site, adding that “a spill of any petroleum is not acceptable”.