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Abstract: Approaches for Reservoir Geological Modelling of the Maui Gas Field, New Zealand

Carl Greenstreet, Ronald The, Jon Cohen

The Maui field currently supplies 90 % of New Zealand's gas and a significant proportion of the country's total energy requirement.

The management of the gas reserves uses an ECLIPSE simulation model based upon the input of reservoir properties from STRATAMODEL. This is a deterministic reservoir geological modelling system suitable for the generally continuous C Sands gas-condensate reservoir and oil bearing F Sands. Reservoir correlations within this lower Eocene coastal plain and shallow marine depositional environment are consistent with reservoir pressure and palaeomagneto-stratigraphic data, supported by a sequence stratigraphic framework and outcrop analogues from the Book Cliffs, Utah. Certain reservoir dis-continuities were interpreted and digitised from seismic amplitude displays and include offlapping shoreface sequences, images of shoreline positions and discrete large-scale valley fills.

Along with gas condensate, the remaining D Sand reservoir contains multiple stacked, but marginal, oil accumulations in fluvial and estuarine channel sands, trapped by extensive intraformational seals caused by base level fluctuations. It is generally a low permeability reservoir, with dis-continuous sediment bodies and possibly sealing, small-scale faults. In contrast with the more predictable C Sands, a combined deterministic-stochastic modelling procedure using Shell's GEOCAP system was found to be most appropriate.

The D Sand property modelling is based on frequency distributions of a large minipermeameter dataset integrated with digital sedimentological core descriptions and supported by systematic mineralogical and petrographic analyses. Some of the potentially productive high permeability meandering fluvial and estuarine channel sands are identified by seismic amplitudes, together with core interpretations and supported by palynofacies data.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France