CHARACTERISATION OF AUSTRALIA'S OIL FIELDS BY FLUID AND RESERVOIR PROPERTIES AND CONDITIONS

Abstract

An extensive data compilation of reservoir rock and fluid properties, and temperature and pressure conditions, in Australia's oil fields, has provided regional information on the nature of crude oil accumulations. It has also allowed the determination of systematic trends and regional variations. These trends and variations are depicted in cross- plots of porosity against depth, porosity against permeability, temperature against depth, pressure against depth, oil gravity against depth, and formation- water salinity against depth.Offshore oil reservoirs, principally based on Gippsland Basin data, are of better quality than onshore ones, even after the porosity cut- off effect is taken into consideration. The Eromanga and Cooper Basins have a higher heat flow than other basins containing oil fields. Pressure trends are consistent with the low salinity nature of formation waters. In Australia, oil reservoirs have an average depth of 1500 m sub- sea and an average temperature of 90°C, and crude oils are light, with an average gravity of 45° API.Interpretation of systematic trends and regional variations can facilitate prospect evaluation by predicting the most likely reservoir qualities and conditions and the fluid properties in potential drilling targets.