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Seismic Inversion For Porosity In The Showgrounds Sandstone.

Dight, Michelle M.

Honours Degree, 1996

University of Adelaide

Abstract

The Showgrounds Sandstone is the primary reservoir in the Western Surat Basin, and produces from the Alton, Silver Springs and Fairymount Fields to name a few. However, due to its thickness, it has been traditionally difficult to define on seismic data and exhibits profound lateral variation in reservoir quality. The aim of this project was to carry out a model-based study to determine whether or not seismic inversion may be a useful tool for porosity prediction in the Showgrounds Formation.

The results of this study show that under certain conditions inversion of seismic traces is successful in estimating acoustic impedance, from which porosity information may be inferred. However, variations in thickness and the presence of shale reduce the accuracy of this method, and the porosity evaluation requires a detailed knowledge of the local geology in order to derive the relationship between acoustic impedance and porosity for each lithology. This thesis outlines the four steps involved in the study: 1) determination of petrophysical parameters for the porosity evaluation; 2) forward modelling to synthesise seismic data; 3) inversion of forward models; 4) analysis of the reliability of the results.

The petrophysical evaluation was performed using 17 wells in the region. However the forward modelling and inversion was concentrated on Grail North #1, in an attempt to examine the effect of velocity variation due to changes in porosity, lithology and fluid content. Both the possibilities and limitations of the method are discussed in the following sections.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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