Canning Basin

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

The northern trough is divided into 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, in which there are thinner sedimentary successions (4–5 km thick) of predominantly Ordovician to Silurian and Permian age, with extensive Mesozoic cover. T

he central arch is divided into the Broome and Crossland Platforms, and structural terraces step down from it into the troughs on either side.

The subdivisions of the basin are based on presently expressed structural elements, although growth faulting initially developed some of these elements, and troughs developed and were active at different times during the basin’s history.The succession in the basin consists of continental to marine-shelf, mixed carbonate and clastic sedimentary rocks. Major evaporitic basins were present in the Ordovician, with lesser such accumulations in the Silurian and Early Devonian. Significant tectonic events affected the basin in the Early Ordovician (extension and rapid subsidence), Early Devonian (compression and erosion), Late Devonian (extension and subsidence), Middle and Late Carboniferous – Permian (compression then subsidence), and Early Jurassic (transpressional uplift and erosion).

The southern Canning Basin is less intensely deformed than the northern part, the major fault block movements being absent in the south.

The offshore Canning Basin contains about 6000 m of Permian and younger sedimentary rocks, with a thick Jurassic to Early Cretaceous section.

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Petroleum exploration activity began in the Canning Basin in the early 1920s when the Freney Oil Company encountered asphaltic shows in drill holes on the Lennard Shelf. Minor exploration continued with Associated Australian Oilfields joining the search.

Exploration intensified when the Bureau of Mineral Resources (BMR, now Geoscience Australia) and WAPET conducted gravity, magnetic, and seismic reflection surveys. Since then, nearly 250 wells have been drilled onshore and 14 offshore. Drilling has been accompanied by acquisition of 110 000 line km of seismic data, 78 000 km onshore and 32 000 km offshore (see WAPIMS)

Up until the mid-1980s, exploration largely focused on the northern and central parts of the Canning Basin. The primary exploration targets were the Devonian and Permian–Carboniferous strata. Many exploration wells had shows, especially of oil, but few yielded commercial hydrocarbons. The basin is substantially under explored, with few wells, of which only a small percentage were valid structural tests.

More recently, the subsalt Ordovician section has been the target of companies such as Shell, who recovered hydrocarbons at its Looma 1 discovery in the southern Canning Basin. Table 6 indicates the formations that either have production or from which substantial recoveries have been made. A selection of additional wells with flow tests or shows is included. There was minor oil production in 2006 from five fields.

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The Fitzroy Trough has been considered to be the most prospective area of the Canning Basin. This is due to its substantial sedimentary accumulation, reefal carbonate buildups along the half-graben hingeline in 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 southern extension of the Kidson Sub-basin. The Ordovician subsalt Looma discovery was the first proof of mature migrated oil from a source pod in the southern Canning Basin, thereby providing a new exploration play.

In the south there is potential for gas generation from the Permian and pre-Ordovician carbonaceous shales and for oil expulsion from shales in the Ordovician Goldwyer Formation. Potential reservoirs are the Nita Formation (Ordovician), Devonian reef complexes, Tandalgoo Formation (Devonian), Yellow Drum Formation (Fairfield Group; Devonian–Carboniferous), Anderson Formation (Carboniferous), 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 fluviodeltaic sandstones are considered to be the primary objectives of the offshore Canning Basin. The producing units of the onshore are deeply buried, thus losing reservoir quality. Thick shales of the Early Triassic and Cretaceous provide adequate seals. Production to date has been primarily from Carboniferous–Permian and upper Devonian reservoir intervals.

Analogs for parts of the Canning Basin include the Paradox Basin of North America, where the Paradox Formation is similar to the Goldwyer, Nita, and Carribuddy Formations. Fractured Ordovician Nita and Goldwyer Formations may be analogous to the Cambrian–Ordovician Ellenburger Dolomite of West Texas. Exploration models from the Devonian reefs of Canada have been applied to those on the Lennard Shelf of the northern Canning Basin.

Permian–Carboniferous clastic rocks may be analogous to those in Saudi Arabia. In Oman, the eastern flank of the South Oman Salt Basin, at or near the edge of the Cambrian Ara Salt, has more than 1907 GL (12 Bbbl) of proven oil in place in analogous Paleozoic to Permian reservoirs.

Four petroleum systems have been identified in the onshore Canning Basin. Proven source-rock intervals are the Ordovician Nambeet, Willara and Goldwyer, and Carribuddy Formations. Global source-rock intervals for the Devonian (Givetian and Frasnian) intervals include the famous Gogo Formation.

The highest source potential of the Devonian Pillara Cycle is in anoxic carbonaceous lithofacies of the back-reef subfacies of the Pillara Limestone and basin facies of the Gogo Formation. The Lower Carboniferous Fairfield Group includes effective source rocks in the Laurel and Anderson Formations that sourced the Lloyd 1, West Kora 1, and Point Torment 1 hydrocarbon accumulations. The Carboniferous and Permian sequences include globally distributed source rocks in the Upper Grant Group shales, Poole Sandstone, and Noonkanbah Formation.

The Ordovician and Devonian petroleum systems (Larapintine 1, 2, and 3) are considered to provide the best prospects for liquid hydrocarbons, with the potential to generate hundreds of billions of litres of oil. Devonian carbonates are productive on the Lennard Shelf (Blina oilfield), whereas the Early Carboniferous has produced mainly oil and minor gas (Lloyd, Sundown, West Kora 1, Point Torment 1). There are also several small oilfields (Boundary, Sundown, and West Terrace) in the Gondwanan-system reservoirs, although the oil is thought to be from Larapintine 3 source rocks of the Laurel Shale.

Play types vary geographically and stratigraphically. Fracture systems associated with transfer faults connecting the Lennard Shelf to the deeper Fitzroy Trough control migration and permeability in the carbonate reservoirs of the Lennard Shelf. Effective intraformational seals control accumulations in siliciclastic reservoirs on the Lennard Shelf. Unconformity traps in rotated fault blocks, draping reservoirs over rotated fault blocks, downthrown rollovers, inversion folds, subsalt traps, and stratigraphic traps remain to be tested within this large, under explored basin.

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