New Zealand Journal of Geology and Geophysics abstracts

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Cyclicity in turbidites of the Miocene Whakataki Formation, Castlepoint, North Island, and implications for hydrocarbon reservoir modelling

B. D. Field

Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
email: b.field@gns.cri.nz

Abstract  Thin-bedded turbidites are a proven hydrocarbon reservoir facies and are recognised in outcrop in the early Miocene Whakataki Formation of the East Coast, North Island, New Zealand. The most likely depositional setting for the unit studied on the East Coast is deep water, marine, levee-overbank, near base of slope. This paper documents characteristics of the unit in outcrop as an aid to understanding likely reservoir modelling parameters for assessments of subsurface reservoir potential of East Coast thin-bedded turbidite facies.
    The thin-bedded turbidites of the Whakataki Formation studied comprise c. 360 sandstone beds in the 32 m thick outcrop section. A notable feature of the beds is that they show bed thickness cyclicity with wavelengths of c. 1 m and perhaps 14 m. Fracture spacing is partly controlled by bed thickness (and hence also cyclicity) but with exceptions. Percent sandstone varies significantly within the section but overall net:gross is 74%.
    The facies in outcrop and its inferred depositional setting are thought to be analogous with gas-bearing thin beds drilled nearby in the offshore at Titihaoa-1, and hence could provide a useful insight into likely reservoir architecture and characteristics at depth.

Keywords  Whakataki Formation; Miocene; Wairarapa; hydrocarbon; reservoir; thin-bedded turbidite; levee; overbank; cyclostratigraphy; cycles; fractures

G02032; Received 1 July 2002; accepted 7 May 2004; Online publication date 23 March 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48: 135–146
0028–8306/05/4801–0135 © The Royal Society of New Zealand 2005

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