ABSTRACT: Computer Simulation of a High-frequency Glacio-eustatic Sequence, Wanganui Basin, New Zealand: Implications to Reservoir Characterization

Liu, Keyu¹, Tim Naish², and Robert M. Carter³
(1) CSIRO Petroleum Resources, North Ryde, Australia
(2) Institute of Geological and Nuclear Sciences Limited, Lower Hutt, New Zealand
(3) James Cook University, Townsville, Australia

A high-resolution sequence stratigraphic model for the Plio-Pleistocene Wanganui Basin sequence, New Zealand was generated using the SEDPAK stratigraphic modelling program. Information which describes the sedimentary facies, chronology, palaeo-water depth, and sea level variation within Wanganui Basin over the last 2.5 my was used to constrain the model. The basin simulation mimics well the basin history, and successfully reproduces both the 40 ky (5th order) cyclothemic packages driven by glacio-estasy, and the large wavelength 4th order cycles which are controlled by the tectonic agents. The high-resolution 2D model for the past 2.52 Ma has a spatial (horizontal) resolution of 500 m, and a temporal (vertical) resolution of 5 ky, and generally mimics closely the observed sedimentary facies, stratal geometry and deposition cycles observed on outcrops.

The simulation results suggest that the glacio-eustatic sea level fluctuation was the primary cause for the formation of the Plio-Pleistocene cyclothems. The model also shows that sediment deposition and preservation is closely related to different locations in the basin, different stages of an eustatic cycle and changes in the rate of sea level fluctuations. The model also predicts significant periods of basin-wide hiatus at cyclothem (sequence) boundaries, which may be as high as 67% in the proximal part of the basin.

The study indicates that quantitative sequence stratigraphic models, such as SEDPAK, are capable of predicting the variations of sedimentary facies in a spatial-temporal resolution that is comparable to typical reservoir sequences, and can be effectively used for reservoir characterization.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia