New Zealand had traditionally been seen by oil-exploration companies as gas country. A major change in attitude occurred in 1979 when Petrocorp, a government-owned exploration company, discovered the onshore McKee oilfield. Although relatively small, it had an enormous effect in demonstrating that oil could be found in the New Zealand region. The offshore Maari and Tui discoveries, made in 1998 and 2003, are predominantly oil.
By January 2005, a total of some 6,258 bcf (billion cubic feet) of gas and 444 million barrels of oil had been discovered in New Zealand. In addition, some 238 bcf of gas and 27 million barrels of oil were found in fields that were still undergoing appraisal. Almost all of it has been found in the Taranaki basin.
The Māui field was among the largest gas fields in the world when found in 1969. It dominates discoveries, having original reserves of 3,439 bcf (billion cubic feet) of gas and 219 million barrels of oil. At 1 January 2005, the field’s oil reserves were estimated to be 92% depleted, and gas reserves were 91% depleted. However, in 2012 new drilling techniques accessing pockets of 'bypass' gass promised to extend the field's life by up to 10 years.
The Taranaki basin covers an area of about 100,000 square kilometres on the west coast of the North Island. Most of the basin, including the Māui field, is offshore. Although much smaller, the majority of producing fields are onshore, largely because it is cheaper to explore and drill there.
In Taranaki more than 350 onshore and offshore wells have been drilled since the mid-1950s, when modern exploration started. Of these, only 120 were wildcats (drill holes testing new exploration targets).
The near depletion of the Kāpuni and Māui gas fields has given added impetus to ongoing exploration and development of new fields.
Discoveries from 1980 to the early 2000s
Some small onshore and offshore fields were discovered in the 1990s and early 2000s in Taranaki. Pohokura, discovered in 2000 off the north Taranaki coast, is by far the largest and will be New Zealand’s second offshore oil and gas field to be developed. The Pohokura platform will be the third to be installed (after Māui A in 1979 and Māui B in 1992). The drilling of production wells from the Pohokura platform was scheduled for 2006.
Since 1980 discoveries include the Maari (1983, oil), Tui (2003, oil), and Karewa (2003, gas) fields. The offshore Kupe field (1986, gas) is expected to start producing in 2008. Onshore finds include the Goldie (2001, oil), Surrey (2002, oil and gas), and Kahili (2002, gas–condensate) fields. Many of these fields are still under appraisal, but all are small.
There was considerable exploration activity during 2004 when 32 wells were drilled. Of these, 17 were being appraised or developing known reserves. Of the 15 exploration wells, two discovered petroleum. During 2004 and 2005, there were large-scale seismic surveys carried out on- and offshore.
The rest of New Zealand is underexplored. Most sedimentary basins have potential, and many untested structural traps could be larger than the giant Māui field. A substantial find is most likely to occur in an offshore basin such as the Great South Basin. Although exploration work, especially offshore, is very expensive, rising oil prices may make more drilling economic.
In the mid-2000s, the government was keen to encourage exploration in other basins, such as the East Coast and Canterbury. It encouraged oil companies by lowering royalties on petroleum finds and providing free seismic data.
Acknowledgements to Richard Cook (GNS Science)