Canning Basin

The onshore Canning Basin covers an area of about 530,000 km² in central-northern Western Australia, and extends offshore for a total basin area of more than 640,000 km², of which 110,000 km² is in State waters. The succession in the onshore basin ranges in age from Ordovician to Cretaceous, but is predominantly Paleozoic. World-renowned Devonian reefs exposed on the Lennard Shelf in the northeast part of the Canning Basin provide excellent insight into the subsurface carbonate geology. The Blina oilfield produces from these reefs.

Two urban centres, Broome and Derby, have shipping and air support and service the Canning Basin. Broome serves as the shipping terminal for crude oil, while minor pipeline grids lie mainly near Derby. Major roads service parts of the basin, particularly near the coast and along the northern margin, where there are settlements and pastoral leases.

The Canning Basin initially developed in the Early Paleozoic as an intracratonic sag between the Precambrian Pilbara Craton and the Kimberley Basin. The basin contains two major northwesterly-trending troughs separated by a mid-basinal arch and flanked by marginal shelves.

The northern trough comprises the Fitzroy Trough and the Gregory Sub-basin, which are estimated to contain up to 15 km of predominantly Paleozoic rocks. The southern trough includes the Kidson and Willara Sub-basins, which are formed by thinner sedimentary successions (4–5 km thick) of predominantly Ordovician to Silurian and Permian-aged sediments with extensive Mesozoic cover.

The central arch is divided into the Broome and Crossland Platforms, with structural terraces that downstep into the troughs on either side. The subdivisions of the basin are based on presently expressed structural elements; however, the troughs developed and were active at different times, with some elements forming through growth faulting.

Petroleum exploration activity began in the Canning Basin in the early 1920s, when the Freney Oil Company encountered asphaltic shows in drillholes on the Lennard Shelf. Minor exploration continued with Associated Australian Oilfields later joining the search in the 1950s, and exploration intensified again in the 1960s and 1970s when the Bureau of Mineral Resources (BMR, now Geoscience Australia) and West Australian Petroleum Pty Ltd (WAPET) conducted gravity, magnetic, and seismic reflection surveys. As of September 2014, 287 onshore and 14 offshore wells have been drilled in the region, accompanied by acquisition of 175,591 km of 2D seismic data, of which 89,587 km is onshore and 86,004 km is offshore.

Up until the mid-1980s, exploration largely focused on the northern and central parts of the Canning Basin. Primary exploration targets were Devonian and Permian strata. Many exploration wells had shows, especially of oil, but few yielded commercial hydrocarbons. Oilfields were first discovered on the Lennard Shelf in 1981. The Blina field was discovered first, followed by the Sundown, Lloyd, Boundary, West Terrace, and West Kora oilfields; the Point Torment gas discovery occurred in 1992. The sub-salt Ordovician section was later targeted by companies such as Shell, who, in 1996, recovered hydrocarbons in the southern Canning Basin well Looma 1.

The Fitzroy Trough and the Lennard Shelf were long considered the most prospective areas of the Canning Basin, owing to their thick sedimentary successions, reefal carbonate buildups along a half-graben hingeline to the north, and structural development in the southwest. Shows in the area confirm petroleum generation and migration.

Other prospective areas of the Canning Basin include the Broome Platform and the Kidson Sub-basin. The Ordovician, subsalt Looma discovery first proved the presence of mature, migrated oil from a source pod in the southern Canning Basin and thereby provided a new exploration play.

In the south of the basin, there is potential for gas generation from the Permian and Ordovician carbonaceous shales and for oil expulsion from shales in the Ordovician Goldwyer Formation. Potential reservoirs are the Nita Formation (Ordovician), the Devonian reef complexes, the Tandalgoo Formation (Devonian), and Permian sandstones. Salt diapirism is evident in the region and may provide traps in areas that lack major block faulting.

Permian, Triassic, and Jurassic fluvio-deltaic sandstones are considered the primary objectives of the offshore Canning Basin. The producing units of the onshore area are deeply buried in the offshore, however, and possess lower reservoir quality. Thick Lower Triassic and Cretaceous shales do provide adequate seals.

The search for shale gas resources in the Canning Basin is in the early exploration phase. However, similarities exist between the Ordovician Goldwyer Formation and gas shales of the United States (US).