Environment groups say the Great Australian Bight is at risk of an "absolutely catastrophic" oil spill should the area be opened to drilling.

On Tuesday, Norwegian energy company Equinor released its draft environment plan for an exploration well around 370 kilometres off the South Australian Coast, claiming the project could be done "safely".

It voluntarily published the plan before submitting it to the regulator, the National Offshore Petroleum Safety and Environmental Management Authority.

BREAKING: Oil giant Equinor has released its so-called 'Environmental Plan' for oil drilling in the Great Australian Bight. This map from Equinor's own prior modelling shows a spill could hit anywhere from SA to NSW. 😱https://t.co/F0pelOVRk9#auspol #protectthebight pic.twitter.com/N3m8tPJqBw — Greenpeace Aus Pac (@GreenpeaceAP) February 18, 2019

But senior campaigner at Greenpeace Australia Pacific Nathaniel Pelle was far from convinced there is anything "safe" about drilling in the Great Australian Bight.

Mr Pelle said that while major accidents are rare, "companies are always only a human error or a couple of mistakes away from having one".

"The first thing you notice when you look at Equinor's published plan is that they hide the most confronting images. Maps that show how far an oil spill could reach are hidden in the appendices," he told SBS News.

Equinor

Wilderness Society South Australian director Peter Owens agreed.

Mr Owens said modelling had shown that a well blowout in the Great Australian Bight could impact anywhere along all of southern Australia's coast, from Western Australia, through SA and Victoria, Bass Strait and north to NSW.

He said a spill could hit Adelaide in 20 days and could reach Port Lincoln and Kangaroo Island in 15 days.

BREAKING: Oil giant Equinor has just lodged plans to push for highly risky deep sea oil drilling in the #GreatAustralianBight. Together we stopped BP & Chevron. Now we will do the same with Equinor. Stay tuned for how you can help - the fight is just starting. #fightforthebight pic.twitter.com/yKZLVRU9Ho — Wilderness Society (@Wilderness_Aus) February 19, 2019

"It's totally irresponsible to be risking the Bight and a liveable climate for our children when the stakes are so high," Mr Owens said.

But the Australian Petroleum Production and Exploration Association said the maps like these detail an absolute worst-case scenario.

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Spills are rare

Equinor's plan goes at length to assuage these concerns.

Equinor's assessment claims while 59,000 offshore wells have been drilled worldwide since 1980, there had only been three large spills and in only one of those, did oil reach the shore.

"The risks associated with drilling exploration wells far offshore are lower because any oil spilled would undergo weeks to months of weathering at sea, during which time its toxicity would be greatly reduced, before reaching sensitive coastal areas," it said.

Equinor said it would also use preventative barriers to minimise the risk of an oil spill and, in the event of a spill, would use multiple layers of well intervention to stop the flow.

It would also employ a range of measures to minimise environmental consequences, including the use of dispersants and the mechanical containment and recovery of any oil.

"Equinor has implemented strict barriers to prevent a spill, prepare intervention and mitigation measures as back-up and is confident that the risk has been reduced," the company said.

It said drilling could start in the summer of 2020/2021.

The Bight

Greenpeace's Mr Pelle said the Great Australian Bight has immense economic value to Australia and is home to a range of biodiversity.

"This place is Australia's whale nursery ... and it likely has the highest concentration of dolphins anywhere in the world," he said.

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"And all the way through the Great Australian Bight runs a reef system that supports billions of dollars in fishing and tourism."

"There are no oil fields there at the moment, there is no heavy industry across the coastline ... The waters are incredibly pristine and we should be protecting the few places on Earth that are in this pristine state."

He said an oil spill "could be absolutely catastrophic. It could have long-lasting effects ... It could cost jobs and would certainly reduce the biodiversity in that area."

Additional reporting: AAP