FILLING HISTORY OF THE MAUI B FIELD, NEW ZEALAND:  NEW INFORMATION FROM OIL INCLUSIONS IN AUTHIGENIC MINERALS FROM THE OIL LEG IN THE MAUI-B1 WELL F SANDS

S. D. Killops^1*,  A. Reyes²  and R. H. Funnell²

A study of the molecular composition of oil inclusions in the Maui field, Taranaki Basin, New Zealand, reveals compositional variation in oil during the filling history of the Paleocene reservoir. The homogenization temperatures of aqueous inclusions in quartz suggest that oil in genetically associated inclusions first reached the proto-Maui structure about 7.0–7.5 Ma ago, and that an effective trap was present at the Paleocene F-sands level, given the abundant oil inclusions. This date coincides with what is believed to represent the early stages of structural development of the trap.  The Maui or Pihama sub-basin appears the most likely kitchen for this early charge. The quartz-included oil exhibits a biomarker distribution with a slightly more marine-influenced signature than an oil stain from the same core plug, oil included in authigenic feldspar, and oil-production samples from the overlying Eocene D sands as well as the F sands. The greater similarity of the feldspar-included oil to the production oils together with its possibly slightly lower maturity suggest that the feldspar inclusions formed later than the quartz inclusions. Otherwise, all oil samples examined (inclusion oil, oil / bitumen in sandstones and producible oil) are of similar maturity.

Key words: Maui field, New Zealand, fluid inclusions in authigenic minerals, reservoir filling history, biomarkers, petroleum migration, petroleum systems.

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