Bass Basin

The Bass Basin is located offshore between the southern tip of Victoria and the northern margin of Tasmania in the shallow waters of Bass Strait. The basin comprises two main sedimentary depocentres, the Cape Wickham Sub-basin in the west and the Durroon Sub-basin in the east. 

History

Petroleum exploration in the Bass Basin began in the early 1960’s with the first well, Bass-1, drilled in 1965. An exploration phase from the mid-1960’s to mid-1970’s discovered gas and condensate at Pelican and five other wells had gas shows. The first commercial discovery (gas with a thin oil leg) was made at Yolla in 1985. Drilling of surrounding structures resulted in further gas discoveries at White Ibis, Trefoil and Rockhopper although Yolla is the only producing field to date. 

Geology

The Bass Basin is a Cretaceous to Cainozoic-aged intracratonic rift basin that formed as part of the Southern Rift System along Australia’s southern margin during regional breakup between Australia and Antarctica. The Bass Basin covers an area of 42,000 km2 and is separated from the Otway Basin to the west by the King Island High, and from the Gippsland Basin to the northeast by the Flinders Island and the Bassian Rise. The basin features a thick sedimentary succession of interbedded sandstones, shales and coals that were deposited in a range of fluvial, fluvio-deltaic and lacustrine environments. For most of its history the basin featured terrestrial environments without major marine influence. Coals and coaly shales form the main petroleum source intervals in the basin. All known hydrocarbons have been discovered within Paleocene to Eocene-aged sandstone reservoirs of the Eastern View Group. Well data shows that the producing intervals tend to comprise multiple, stacked reservoir-seal pairs.