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Publication highlights oil-bearing formations - 11/07/2000

A new publication on the geology and oil and gas prospectivity the Great South Basin – a large offshore area southeast of New Zealand – is expected to raise the level of interest in this area by exploration companies.

It is the most comprehensive study available on this large sedimentary basin – the least explored of New Zealand’s near-shore oil and gas areas.

Though some of the information has been released independently over the past 10 years, the publication marks the first time all the information has been presented in a single bound volume. The Great South Basin contains many large untested geological structures, some potentially larger than Taranaki’s Maui natural gas field, that have all the right components for oil and gas.

" Four of the eight exploration wells that have been drilled since the 1970s have produced sub-commercial quantities of gas condensate. There is ample evidence that this basin contains significant volumes of liquid and gaseous hydrocarbons," lead author and petroleum geologist Richard Cook said.

Oil seeps on Stewart Island provide on-land evidence of the basin’s worth.

The Great South Basin covers 100,000sqkm, or about 66 percent of the area of the South Island. It extends from offshore Otago to sub-Antarctic waters 300km south of Stewart Island. There are currently no exploration permits in what geologists describe as a moderately high risk area with the potential for high returns.

Water depth in the Great South Basin ranges between 100m and 1250m with an average of about 700m. However, Dr Cook said even the deepest parts of the basin were well within the capabilities of today’s drilling and production technology.

Titled Cretaceous-Cenozoic geology and petroleum systems of the Great South Basin, the publication represents a mammoth effort by scientists at the Institute of Geological & Nuclear Sciences Limited (GNS). Up to 25 scientists, including world renowned specialists, have contributed to the publication.

Dr Cook said the publication would be invaluable for exploration companies wanting to understand the geology of the area and find out the most likely areas to drill for oil and gas.

" It has drawn on a variety of sources including petroleum exploration company records and many unpublished studies. This has been synthesised with our own extensive research and interpretation. The result is an unprecedented reference for oil exploration companies."

The publication extended the understanding of the oil and gas prospectivity through improved interpretation of offshore seismic reflection survey data, which provides images of rock formations up to 10km below the seabed.

Using source rock geochemistry and subsurface mapping, GNS scientists had produced computer models of where oil and gas is likely to have accumulated.

Dr Cook said the publication was likely to remain an important platform for exploration for many years. It was funded through the government’s Foundation for Research, Science and Technology.

It is the eighth publication GNS has produced on New Zealand’s main sedimentary basins. Earlier publications cover Northland, Taranaki, East Coast North Island, West Coast South Island, Canterbury, Western Southland, and the Chatham Rise.

The Taranaki publication has played a role in helping oil exploration companies find and successfully extract billions of dollars worth of oil and gas.

The Great South Basin publication is available from GNS for $120.

For more information contact:
Dr Richard Cook,
Petroleum Geologist Richard Cook
or Dr Rupert Sutherland,
Geophysicist and co-author, Rupert Sutherland