--> Abstract: South Wanganui Basin, New Zealand-Frontier Oil and Gas Potential, by T. L. Thompson, C. V. Hagen, B. T. May, and J. A. Brown; #91015 (1992).

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ABSTRACT: South Wanganui Basin, New Zealand-Frontier Oil and Gas Potential

THOMPSON, THOMAS L., CECIL V. HAGEN, BRUCE T. MAY, and JEFFREY A. BROWN, Boulder, Colorado

The South Wanganui Basin represents an essentially unexplored area (only 5 wells) of about 5 million acres located onshore and offshore in the southwestern part of the North Island, approximately 70 miles north of Wellington, and just east of the petroleum productive Taranaki Basin which includes two world-class gas condensate fields, Maui and Kapuni. The deep part of the South Wanganui Basin reasonably brings together in a favorable time and place framework all essential ingredients for petroleum accumulation including: mature organic source, favorable migration paths, sandstone reservoirs, structural and stratigraphic traps and mudstone seals.

The subject basin contains at least 13,000 feet of rapidly deposited late Miocene and Plio-Pleistocene sediments, including at the base several thousand feet of transgressive, non-marine to marine, sedimentary rocks that may represent petroleum source potential because of its possible content of organic-rich coastal deltas, lake deposits, coal swamps and lagoons. Interbedded lower Pliocene sandstones and mudstones represent good reservoirs and seals. Several coastal and nearshore marine sandstones show porosities of 20-35% with permeabilities of 300-400 md.

The rapid crustal downwarp that formed the South Wanganui Basin (a convergent margin proto-arc basin) reasonable results from some combination of deep crustal drag related to the west dipping bend in the Alpine-Ruahine fault zone, sediment loading and perhaps thrust loading. The Jerusalem (or Mangapura) warm springs and a high thermal gradient in the Parakino well suggest subterranean propagation of the Taupo Volcanic arc beneath the South Wanganui Basin, perhaps related to the releasing fault bend.

Thermally mature source for petroleum seems assured by the combination of high potential Miocene coal measures in the Manutahi well (900 barrels per acre foot), high geothermal gradient in the Parakino well and migrated higher hydrocarbons at Jerusalem warm springs. Possible structural traps include those mapped by seismic interpretation plus those inferred by tectonic integrity, surface mapping and gravity. Topographic relief on the basement, the non-marine to marine transgressive stratigraphic onlap, and the coastal sedimentary environmental complex all suggest potential for stratigraphic traps.

 

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)