Over the next three years, Victoria’s Gippsland Basin is scheduled for three deepwater wells, the Otway/Sorrell region, which spans Victoria, South Australia and Tasmania, is slated for two wells and there could be one in the waters of the Great Australian Bight.

This last well, Woodside’s Springboard-1, would be drilled about 100km west of the region’s last well, the same company’s Gnarlyknots-1, which was drilled in 1300m of water during 2003.

While Gnarlyknots was abandoned prematurely because of deteriorating weather, it found high-quality sandstone reservoirs, marine shale seals and the inferred presence of a mature hydrocarbon kitchen area down-dip – enough encouragement for Woodside to continue the program.

Most of wells planned on the southern margin are seeking oil, and hope to debunk the entrenched view among explorers here and abroad that deepwater Australian exploration will yield only gas.

In the Gippsland Basin, wells are planned in VIC/P59 (operated by Sita Oil) and VIC/P60 (operated by Holloman) to test for deepwater extensions of the prolific Bass Strait oil fields. VIC/P59 is near the Blackback oil field, which was Australia’s deepest producing field from 1999 until Woodside commissioned Enfield last year.

The unsuccessful Ait-1 well, drilled by Santos in 2004, is the Otway Basin’s only deepwater well. The host permit was subsequently relinquished but Santos continues to maintain deepwater interest in the adjacent Sorrell Basin, where it operates five permits down the west coast of Tasmania, one in which it holds 100% and four others in various partnerships with Chevron, Inpex and Mitsui.

The Sorrell is one of Australia's least explored regions with only two exploration wells drilled so far. Its five sub-basin depocentres have sediment thicknesses between 3km and 6.5km. Santos says its geological studies indicate working petroleum systems that have led to exploration success in the eastern Otway are likely to extend southwards into the Sorell.

The company has two commitment wells due in this basin in 2007, although these are not in the company’s current exploration program.

But the continent’s southern margin is notoriously difficult for deepwater exploration. Severe weather restricts deepwater drilling activity to between October and April, and whale migration can further reduce drilling opportunities.

Only seven deepwater wells have been drilled off southern Australia, and none in the southwestern or southeastern margins.