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ABSTRACT: Forgotten frontiers in Western Australia: the Southern Carnarvon Basin

Mory, Arthur J. , Geological Survey of Western Australia, Perth, Australia

After the surprise in 1953 of an oil discovery from the first well drilled in the Carnarvon Basin at Rough Range (still sub-commercial), exploration quickly moved further north and offshore into the Northern Carnarvon Basin (covering 435 000 km2) where seismic acquisition is much cheaper. In that basin 50 significant fields have been discovered since 1964, of which 28 are currently producing. By comparison, the Southern Carnarvon Basin (covering 185 000 km2) has languished largely because the first shows were minute in contrast to large offshore successes, and the industry barely commenced to evaluate this largely Palaeozoic onshore intracratonic/rift basin. Contrary to many of the present beliefs, much of the basin is still in the oil window, and source-rock quality in the Upper Devonian and Permian is good to excellent with TOC up to 13.6% and potential yield up to 17.7 mg/g rock. Potential seals up to several hundred metres thick are widespread, as are Lower Permian reservoirs with log-derived mean porosities of 12-21% and permeabilities up to 3180 md and, to a lesser extent, Devonian sandstone and reef or fractured carbonates. In addition, geophysical mapping indicates there are many untested structural plays, but none of the existing exploration wells (mostly drilled over 20 years ago) appear to have been valid tests below the generally thin Cretaceous section. A success in this region would have hundreds of follow-up prospects. Considering that just 19 exploration wells have been drilled in this frontier area compared to over 340 in the Northern Carnarvon Basin, and that infrastructure is in place as the Dampier-Perth gas pipeline runs along the eastern side of the basin, further exploration efforts are more than warranted.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia