Controversial seismic testing looking for oil under the seabed off Northland's west coast is expected to start in December.
But it will be another six years before oil or gas is drilled for in the area if it is viable, the company behind the exploration says.
The Norwegian oil firm Statoil last year won a tender to explore 9800sq km of the Reinga Basin, about 100km off Ninety Mile Beach, for oil.
Seismic testing uses sound "explosions" to map rock formations under the seabed and is commonly used in the search for hydrocarbons. It is, however, controversial.
Statoil spokesman Pal Haremo said in 40 years of oil exploration the company had not recorded any permanent damage to marine mammals.
Otago University associate zoology professor Liz Slooten, on the other hand, said it could lead to more whale strandings and leave some whales and dolphins effectively deaf and blind.
The first step in the company's exploration was carried out over 10 days in June.
The Niwa research vessel Tangaroa was used to create a 3D map of the sea floor using a fan of sound beams sent out by instruments on the ship's hull, known as "swath multi-beam bathymetry".
Mr Haremo said the data was still being interpreted. It would be used to choose up to 50 points on the sea bed to drill for core samples in April-June next year. Samples would be just a few metres deep and would be used to learn more about the seabed's geology.
The seismic testing was due to begin in December. Norway-based seismic contractor TGS would spent 3-6 months surveying Statoil's area plus a larger area oil companies had yet to bid on. TGS could then sell the data to other oil companies in future.
Based on the first three years' worth of findings, Mr Haremo said Statoil would decide in March 2017 whether to give up its permit or keep exploring.
If it continued it would then collect 1000sq km of 3D seismic data in the hope of finding structures below the sea floor likely to contain oil or gas. If the results were still promising the first exploration well could be drilled in 2020.