Blow-up over oil blowout study

Large amounts of crude oil battered the Alabama coast, leaving deposits of the slick mess some 10-15cm thick on the beach.

New oil spill models have depicted the dramatic impact deep-sea blowouts would have on New Zealand, spreading across our most important fishing ground and hitting Auckland's iconic west coast beaches.

The report, commissioned by Greenpeace and produced by data science agency Dumpark, sought to gauge the blow-out effects of two planned deep-sea drilling locations off the North Island's west coast and the South Island's east coast.

But an industry spokesperson last night slammed the study as inaccurate, "fear-mongering" and "science fiction", while Government officials also described such a large-scale spill as unlikely.

In the environmental impact assessment it last month lodged with the Environmental Protection Authority for its Taranaki operation, the company conceded a loss of well control would hold "significant impacts" for the environment, but stated this was "extremely unlikely".

A model in the assessment, showing a summer spill, depicted a 51 per cent chance of oil reaching the coastline, with a sweep taking in the west coast of Auckland the most likely area to be affected.

Anadarko had submitted a detailed oil spill trajectory map to Maritime New Zealand as part of its discharge management plan.

Greenpeace's report used a decade of ocean and climate data and industry-standard numerical modelling techniques to depict how oil would travel and disperse if a blow-out happened.

"We predicted the trajectory of a thousand oil spill scenarios at two sites in New Zealand using 10 years of global archives of marine weather data," Dumpark ocean modeller Laurent Lebreton said.

Assuming a scenario where oil flowed into the ocean over 76 days in summer at a rate of 10,000 barrels per day, the analysis for the north showed the likelihood of oil hitting Auckland's western beaches and harbours.

The report's North Island scenario painted dramatic consequences for the entire western coastline and harbours from Taranaki's Cape Egmont to Opononi in Northland.

Read the full North Island and South Island reports online.

In the south, a spill off the coast of Otago could spread across the Chatham Rise, our most valuable fishing ground, and reach all the way to the Chatham Islands.

The report determined that a continuous spill in the north would likely affect an area of more than 226,000sq km after 76 days in summer, and more than 532,000sq km over the same period in the south.

Greenpeace campaigner Steve Abel accused the Government of understating the "real risks" being taken with the country's oceans and coastlines.

He said the report revealed the "full extent of the risk of deep-sea drilling".

"Drilling at these depths is much riskier than the shallow drilling we currently have in New Zealand."

Green MP Gareth Hughes said the modelling showed a deep-sea blowout would have "huge consequences". "While there are some short-term economic benefits to deep-sea drilling, they don't justify risking a huge spill that could cost us billions."

Labour's energy and resources spokesperson, David Shearer, said his party did not rule out deep-sea drilling but expected that any companies making applications would have to be "world class" and demonstrate they had robust safeguards in place.

Professor Rosalind Archer, head of Engineering Science at the University of Auckland, said the report gave no evidence that a spill rate of 40,000 barrels per day - the largest of the rates modelled - was reasonable for a New Zealand well.

Rates would also normally decline as the well flowed, and the study also appeared to assume nothing was done to constrain the well rate over the 76-day window considered.

David Robinson, chief executive of the Petroleum Exploration and Production Association New Zealand (PEPANZ) meanwhile accused Greenpeace of being "absolutely dead against" the petroleum sector, and said the report was trying to "frighten Kiwis".

He said the geological environment in which the Deepwater Horizon disaster took place, pumping 5 million barrels of oil into the Gulf of Mexico in 2010, bore little resemblance to that of New Zealand.

Environment Minister Simon Bridges also believed a large spill was unlikely.

More than 200 offshore wells had been sunk to date, eight of which were in deep sea of more than 300m. The largest event on record was the 23 tonnes of oil that spilled from the Umuroa FPSO on the offshore Tui Field in 2007, an amount much smaller than the 350 tonnes spilled from the MV Rena in 2011.

Oil from the Deepwater Horizon has affected wildlife throughout the Gulf of Mexico.

Greenpeace New Zealand commissioned Dumpark to map out how a large deep-water oil spill would travel at two proposed exploration sites off the coast of New Zealand - the west coast of the North Island in the Taranaki Basin and the east coast of the South Island in the Canterbury Basin.

The analysis drew on industry standard numerical modelling techniques to map the trajectory and determine the extent of oil propagation, dispersion and beaching in the event of a deep water blowout.

The report described the impact analysis for Taranaki and Canterbury after 76 days of continuous spilling at a flow rate of 10,000 barrels per day during the summer season.

During the Deepwater Horizon disaster in the Gulf of Mexico, the flow rate reached 62,200 barrels per day on April 22, 2010, and dropped to 52,700 barrels per day almost three months later.

The report factored in socio-economic and ecological thresholds for both land and sea. The "socio-economic threshold" related to closure of fisheries at sea - the limit being 0.01 grams of oil per square metre - or shoreline clean-ups on amenity beaches, with a limit of more than one gram per square metre.

The "ecological threshold" - more than 10 grams per metre square - integrated degrees of oiling known to kill seabirds and other wildlife.

The model results showed a "significant impact" on the shoreline for nearly the entire west coast of the North Island, with oil thickness reaching levels as high as nearly 250 grams per square metre in some areas, well above the ecological threshold. The combined North Island area, covered by 95 per cent of the modelled trajectories and exceeding the socio-economic threshold, grew to 15,500sq km after one week, 132,400sq km after one month and 226,800sq km after 76 days.

In Canterbury, the report found the extent of the probabilistic spread was much larger than for Taranaki as most spills drift freely across the ocean for months without encountering land. The model showed a wide impact plume that extends eastwards as far as the Chatham Islands.

The socio-economic threat zone grew from an area of 14,300sq km after one week to 162,100sq km after a month and 532,400sq km after 76 days.

The threshold for socio-economic impact at sea was reached at 91 per cent of trajectories for the coastal waters of Kaikoura and between 21 and 44 per cent for Oamaru, Banks Peninsula and Taiaroa Head.