THE CEDUNA SUB-BASIN—A SNAPSHOT OF PROSPECTIVITY

Abstract

The Ceduna Sub-basin comprises one of the major untested potential petroleum provinces in Australia. It is located in the Great Australian Bight, forming part of the Bight Basin. Water depths range from 100 m in the north to over 4,000 m in the south. Although over 100,000 line km of 2D marine seismic data have been acquired in the Great Australian Bight, only 20,600 line km of 2D marine seismic data of variable vintage and quality have been acquired in the Ceduna Sub-basin. Only one exploration well, Potoroo–1, has been drilled within the Ceduna Sub-basin. The Potoroo–1 well is located on the extreme landward edge of the depocentre which is dominated by the Late Cretaceous Ceduna Delta. Consequently, the hydrocarbon potential of the basin is effectively untested.

The most promising play types within the Ceduna Subbasin are dip and fault-dip closures associated with listric faults within the Late Cretaceous (Santonian- Maastrichtian) deltaic sequence and accentuated by slight Late Cretaceous/Tertiary compression. Fault-dip closures are also recognised within the Santonian section. A channel sub-crop play within the Santonian is also potentially viable.

Hydrocarbon charge is perceived to be the most significant exploration risk. Although asphaltite strandings have been reported, the hydrocarbon charge system is unproven. Future exploration in the Great Australian Bight will need to address:

harsh climatic/meteorological and oceanographic conditions in the Southern Ocean and short seasonal windows;

extreme sea floor relief and viability of safe exploration drilling in water depths over 1,500 m; and

operating in a responsible and environmentally sensitive way in proximity to the Benthic Protection Zone.