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Some significant data are here revealed for the first time, covering the 10-year oil exploration program of New Zealand's vast South Island submerged plateau.
A 250,000-sq mi (650,000 sq ha.), Texas-sized group of licenses was taken by Hunt International Petroleum Co. in 1968 and 1969. About 26,000 line-mi (41,600 line-km) of marine, 12-fold seismic survey, was completed over a 4-year period. Much of the survey extended to 4,500-ft (1,350 m) water depth.
Tectonics are controlled by the separation and splay of New Zealand's backbone Alpine fault system as it swings southeastward across the Campbell Plateau toward Bounty Island and the Antipodes. Basement is of Paleozoic age. Lower Mesozoic sediments resulting from orogenies and plate shifts are relative to Mesozoic Gondwana breakup.
Six previously unknown Tertiary basins, large by basin standards, were discovered. The interpretive mapping revealed 30 to 40 giant to supergiant anticlinal structures and an equal number of normal ones, mostly in water depths exceeding 2,000 ft (600 m). The several prospects drilled indicate nearly 18,000 ft (5,400 m) of Tertiary and Cretaceous sediments, with several thousand feet being mature and hydrocarbon generative. Drill-stem tests recovered oil and gas in one wildcat, and two others had oil and gas shows.
By late 1978 the first-phase, 7-well exploratory program was completed. Two of the six basins had been tested. Individual wildcat costs using an anchored semisubmersible rig are in the $10 million to $20 million range.
Despite adverse factors of extreme weather conditions, deep water, remoteness, and high drilling costs, more exploratory drilling will be necessary for final evaluation. The Sea Hunt Group is presently considering its second-stage drilling program for the area.
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