RESERVOIR CHARACTERISATION OF A LOW RESISTIVITY GAS FIELD-OTWAY BASIN, SOUTH AUSTRALIA

Abstract

The Katnook, Haselgrove and Ladbroke Grove Fields of southeastern SA are characterised by a lack of resistivity contrast above and below known gas-water contacts, poor hole conditions, complex mineralogy and fresh formation water. A multi-disciplinary review of all available data to characterise the Pretty Hill Sandstone reservoir by integrating core, log and engineering data has enabled a comprehensive picture of reservoir heterogeneity and its influence on log response and well performance to be determined. The availability of extensive core throughout the 6 wells has resulted in the accurate modelling of reservoir porosity and the derivation of a facies-dependent, quantitative permeability log which closely matches drill stem test and production test derived permeability thickness (kh). Previous water saturation assumptions have been shown to be optimistic with Leverett J Function water saturation averaging 50-60 per cent through the reservoir. Detailed facies modelling from the cores extrapolated into areas with no core control has led to the derivation of a geological model which, when integrated into a 3D simulation, has resulted in calculated pressures within 1 per cent of those measured and has enabled the prediction of the pressure response from highly compartmentalised portions of the reservoir. Simulation-derived, material balance and volumetric original-gas-iti-place for the Katnook Field now agree to within 5 per cent.

The study has resulted in changes to previously accepted evaluation procedures for wells targeting the Pretty Hill Sandstone.