ASSESSMENT OF THE SEAL POTENTIAL OF TERTIARY CARBONATES, DUNTROON BASIN, SOUTH AUSTRALIA

Abstract

The seal potential of the Wilson Bluff and Nullarbor Limestone Formations was assessed over high-graded Pidinga Formation leads of the Duntroon Basin that contain significant hydrocarbon potential. The work quantified the risk associated with these plays. Regional geological knowledge was integrated with the results of special core analysis and petrography to address the 3 critical aspects of seal quality: seal capacity, seal geometry and seal integrity.

This work established a clear relationship between seal potential and lithofacies, namely, the higher the clastic content, the better the seal potential. More specifically, in the vicinity of the Tertiary channel system and clastic axis, the seal risk for the Wilson Bluff Formation carbonates is considered to be relatively low, since it contains a significant argillaceous component. A maximum oil column of up to 650 m could be contained, with a more likely column of approximately 20–75 m. With increasing distance from the channel system, there is a decrease in argillaceous content and an associated increase in seal risk, the size of the oil column that could be contained varying from 2 m to 300 m, the more likely being 2–20 m. The Nullarbor Limestone is considered to be a relatively poor seal as a result of extensive development of secondary porosity during diagenesis. A maximum oil column of 160 m could be contained, the more likely column being approximately 5–30 m.