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Major Marine Seismic Survey Gets Underway



The Institute of Geological & Nuclear Sciences Limited (GNS) has joined forces with TGS-NOPEC Geophysical Company, a leading provider of seismic data to the international oil exploration industry, to conduct a large seismic survey in deep water off the North Island’s west coast.

The survey, which will acquire 6800km of high quality seismic data in water depths ranging from 200m to 1800m, is hoped to be a forerunner of a major petroleum exploration effort in the Tasman Sea.

The data will be collected in the previously unexplored Deepwater Taranaki Basin, regarded by GNS as the most attractive of New Zealand’s deepwater sedimentary basins. It will be New Zealand’s first large-scale marine reconnaissance seismic survey targeting oil prospectivity for more than two decades.

GNS researchers first investigated the region in 1988. They suspected the area contained a sedimentary basin, but the information available was not good enough assess its petroleum prospectivity.

In 1997, a single deep penetration seismic line was shot from the Taranaki Shelf edge for 1000km along the axis of the New Caledonia Basin. This seismic line was aimed at defining the future boundary between Australian and New Zealand territorial waters and is jointly owned by the New Zealand government and the Australian Geological Survey Organisation.

When the data was analysed, it revealed a surprisingly thick sedimentary section in the deepwater extension of the Taranaki Basin. The sediments were deposited between 65 and 144 million years ago and form a layer at least 5000m thick.

GNS researchers have inferred from the 1997 data that much of this sedimentary section consists of a large delta. Deltas are important sources for petroleum around the world and the presence of a delta in the basin adds considerably to its oil prospectivity.

The alliance between TGS-NOPEC and GNS is the outcome of several years of research and promotion by GNS senior geophysicist Chris Uruski. Mr Uruski has studied this area for many years, and was on the survey ship that collected the single seismic line in 1997 that has "seeded" the project.

" The scant existing data of the Deepwater Taranaki Basin shows potentially oil-bearing rocks at least 8km thick - thicker than the average oil-bearing formations in the Taranaki Basin," Mr Uruski said.

GNS researchers believe that the sediments in the Deepwater Taranaki Basin were deposited at the same time that rich, black marine shales were being deposited in many of the world’s main oil provinces. These shales are the key source rock that leads to the formation of oil in these areas.

The survey is scheduled to start within the next 10 days and will be conducted by the Polar Duke, a specialist seismic survey ship. It is expected to take three months to collect the data from the 59,340sqkm permit area and a further six months to process it. GNS scientists will interpret the processed data and provide TGS-NOPEC with an interpretation report.

The high quality seismic data will enable scientists to build a much clearer picture of the geology of the basin and help define the size and nature of petroleum traps.

It is a "non-exclusive" survey, which means that TGS-NOPEC will license both the data and the report from GNS to several oil companies at the same time. This enables the oil companies to spread the risk in a new area, and identify structures they believe may contain oil or gas before applying for an exploration permit.

" Only the larger oil companies can explore deepwater prospects, and TGS-NOPEC is marketing this project right around the world," GNS Seismic Processing Manager Guy Maslen said.

In a recent survey by the international IHS Energy Group, New Zealand was upgraded as a more attractive region for oil exploration investment, and this survey promotes both New Zealand and GNS, Mr Maslen added.

The Crown Minerals section of the Ministry of Economic Development will licence the area for exploration in early 2002. Oil exploration companies will be able to use the GNS/TGS-NOPEC survey data to decide on which areas to bid for.

Before drilling, companies will most probably acquire more complete seismic coverage over the most promising structures. This may include acquiring a three-dimensional seismic survey, where a relatively small area is surveyed at high resolution to build a complete 3D image of the subsurface structure.

" GNS will have full access to the data for scientific research into the geological development of New Zealand. TGS-NOPEC is a significant industry player, and we are already looking ahead to other poorly explored areas where we could work together," Mr Maslen said.


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