--> Paleozoic Basins of Western Australia: Conventional Plays Abound

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Paleozoic Basins of Western Australia: Conventional Plays Abound

Abstract

The potential of Western Australian onshore Paleozoic basins may be of great interest to companies active in similar North American basins where there is greater exploration maturity and fewer opportunities for discovering significant new conventional oil provinces. The three main Paleozoic basins with petroleum potential in Western Australia, are the Canning, Southern Carnarvon and Bonaparte basins. After the discovery of the Blina oilfield in a Devonian reef in the large Canning Basin in 1981, Western Australia's onshore Paleozoic basins attracted a number of players including Canadian and US companies, and exploration accelerated. In the 1980s a number of small fields discovered in Permo-Carboniferous clastics also came into production along the northern margin of the Canning Basin. The area came off the boil after the oil price crashed in February 1986 and a stockmarket correction in October 1987. The exploration spotlight shifted from the onshore Canning Basin to the offshore North West Shelf, where new commercial production started coming onstream from the Northern Carnarvon Basin. Interest has returned to the Canning Basin in recent years. In 2011 oil was discovered in dolomitised limestones of the Carboniferous Laurel Formation with the Ungani 1 well. The original target was gas, a sign that the basin may yet provide further pleasant surprises. In addition to proven supra-salt plays (Devonian reefs, Permo-Carboniferous clastics and Carboniferous carbonates) there are sub-salt Ordovician carbonate and sandstone plays which have yet to be proven commercially. In the frontier Southern Carnarvon Basin, geohistory modelling by the Geological Survey of Western Australia indicates that petroleum generation and migration peaked during the Permian for Silurian–Devonian source beds (oil and gas potential) and during the Triassic for Permian source beds (mostly gas prone). The main Paleozoic plays are considered to be Devonian reefs and sandstones as well as Carboniferous-Permian sandstones. In the onshore Bonaparte Basin, gas has flowed to the surface in subcommercial quantities from the Carboniferous Milligans Formation sands. Tight sandstone and limestone reservoirs in the Carboniferous Langfield Group are also a target in the basin. There is room for further Paleozoic hydrocarbon discoveries in Western Australia and it is up to companies with foresight and determination to unlock the location of potential productive fairways.