New Zealand Journal of Geology and Geophysics abstracts
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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