New Zealand's many deepwater basins have the best potential for big oil discoveries, frontier basins petroleum scientist Chris Uruski says.
All of New Zealand's frontier basins explored to date have been winners in terms of finding the right conditions for petroleum generation, according to Uruski.
"We have yet to come across a basin which does not have the necessary sedimentary depth and an active petroleum system," Uruski, a geophysicist with GNS Science, told the recent NZ Oil and Gas conference in Wellington.
New Zealand is currently in the midst of initial exploration of many of the deepwater basins which cover an area of approximately 1.2 million sq km -- about five times the size of New Zealand's land area of 250,000 sq km.
The deepwater basins lie on the mostly submerged Zealandia continent, which is similar in size to the land area of Australia. New Zealand’s offshore territory in the EEZ and extended continental shelf covers 5.8 million sq km. Uruski said a number of large offshore structures had been revealed to date in deepwater basins.
In the Great South Basin a four-way dip structure called the Hokonui High, which was revealed by data from the 2006 Crown Minerals survey, showed a 113 sq km structure over a basement high could contain potential P50 reserves of 500 million barrels of oil-in place or 2 trillion cubic feet of gas. The Hokonui High lies in 1,200 m of water over 100 km south of Dunedin.
In Deepwater Taranaki Basin the Romney prospect with a closure area of 200 sq km in 1,600 m water depth was estimated to contain 1,100-1,650 million barrels of oil-in-place or 1.7-2.7 TCF of gas.
Right next to Romney the Coopworth prospect was estimated to contain 360-540 million barrels of oil-in-place or up to 1 TCF of gas.
The Government through Crown Minerals in recent years has carried out seismic surveys over deepwater basins part of the Great South Basin, the Raukumara Basin (north of East Cape), Northland and Reinga Basin (north-east of Northland) while another major survey by a private company was carried out over the Deepwater Taranaki Basin.
Another seismic survey for Crown Minerals by the seismic vessel Bergen Resolution is underway over the Pegasus Basin (south of Wellington), eastern Great South Basin and a part of the neighbouring Bounty Trough (east of Otago-Southland).
Reconnaissance data will also be acquired over the Challenger Plateau and Bellona Trough (both west of Nelson), the Outer Taranaki Basin (west of Auckland) and the Northland East Slope Basin area north east of Auckland.
Uruski said New Zealand's deepwater basins were estimated to hold total petroleum resources of at least 20 billion barrels of oil equivalent.
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