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A Regional Rock Property Model for Triassic & Jurassic Sediments of the Western Dampier Sub basin

Hickson, Alison B.

Honours Degree, 2006

University of Adelaide

Abstract

The high resolution Demeter 3D Seismic Survey was acquired in 2003-04 and covers most of the North West Shelf Joint Venture Area in the Dampier Sub-basin. As part of the revitalised exploration efforts it was deemed worthwhile to attempt to develop a regional rock property model for the Jurassic and Triassic formations. Interpreters could use this to forward model different lithological and fluid scenarios for a prospect to then compare to the seismic response.

Functions were fitted to wireline log data acquired from 55 wells in the Dampier Sub-basin to model porosity, density and velocity for the Mungaroo, Brigadier and North Rankin Formations as well as soft shales above the Main Unconformity and the Windalia Radiolarite. These functions were then evaluated against wireline logs with a sensitivity analysis also conducted to determine the impact of the scatter on these variables to validate the usefulness of the model.

The study has shown that a regional rock property model can provide some benefit as a risk reduction tool by reducing the number of possible geological scenarios. However ambiguity does exist between some scenarios, the most important being the similarity in properties between high porosity brine filled sandstone and an average porosity, 80% gas saturated sandstone. This ambiguity is the result of the acoustic impedance being more sensitive to velocity as an input variable then density. The significance of this result is that separation between lithology and fluid fill is achieved from density and not velocity.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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