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Geological Assessment and Hydrocarbon Volumetric Reserve Estimation of the Urania Field, North West Shelf, Australia

Alexander McINNES
Bachelor of Science Hons (Petroleum Geology & Geophysics 2013
Australian School of Petroleum
University of Adelaide

Abstract

The Exmouth Plateau on Australia's Northwest Shelf has been a focus for petroleum exploration since 1979, due to discoveries of giant gas fields such as Scarborough and Jansz-lo. This study focuses on the Urania Gas Field, located within the northeastern region of the northern flank of the Exmouth Plateau. The principal aim of the study was to complete a geological assessment of the Urania Field, with the final result being the estimation of the total gas in place within the field.

The Urania Gas Field contains an interpreted maximum gas column of approximately 45 metres, reservoired within two Late Triassic fluvio-deltaic sandstones namely the AA and C reservoirs. The Urania structure is a northeast-southwest trending three-way footwall closure, with the main sealing lithologies being Late Triassic and Early Jurassic shale and silts units.

The available dataset for the project included the Willem and Pluto North 3D seismic surveys and the wire-line logs from the Urania-1 and several other regional wells. The integration of the seismic and well data allowed for a structural and stratigraphic framework to be developed over the project area, which was used to create time and depth structure maps for use in final volumetric reserve calculations.

Integration of interpreted depth structure maps and reservoir properties calculated from the original wire-line log suite allowed the calculation of three hydrocarbon volume estimates. One utilised the average porosity, water saturation and net to gross ratio over the reservoir interval, while the other two used the highest and lowest porosities, water saturations and net to gross ratios over the reservoir intervals respectively. The average estimate suggests that there is approximately 300Bcf of gas within the two reservoir units of Urania Field, with the majority being contained within the deeper C reservoir. As the gas accumulation within the Urania Field is relatively small, and at subsea depths greater than 3000 metres, the economic potential of the field at current market conditions is interpreted to be relatively low.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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