The Carnarvon Basin blocks are offshore Dampier (combined release area L15-2 and T15-1), Cape Preston (L15-3) and Onslow (L15-4) on the south-eastern margin of the prolific Northern Carnarvon Basin.

In recent years, the entire basin has contributed to over 90% of hydrocarbon production in WA and half of the total production in Australia, and has become an area of renewed focus, with companies such as AWE, Tap Oil and Finder Exploration looking at previously explored areas with new ideas, in part chasing plays worked up since the discovery of Triassic oil in the Phoenix South-1 well.

T15-1/L15-2 and L15-3 cover about one graticular block (80sq.km) each and lie in the Dampier Sub-basin, whereas the much larger 480sq.km L15-4 lies mainly on the offshore Peedamullah Shelf and extends westward into the Barrow Sub-basin, across the Flinders Fault System.

All are close to infrastructure servicing the oil and gas industry, including an extensive network of pipelines links offshore gas fields to Quadrant Energy's Varanus Island hub, and gas processing and LNG plants in Karratha, Dampier and Devil Creek.

The Wheatstone LNG and gas processing plants are under development near Onslow, and there are several small undeveloped oil fields near to the blocks, such as Saladin and Australind.

There is no well within any of the Dampier Sub-basin release areas and mixed seismic coverage, while L15-4 contains three well penetrations, and the block is largely covered with vintage 2D and 3D.

T15-1/L15-2 is just 90km south of the Legendre field, which was discovered by Woodside Petroleum in 1968, the first offshore well in the northern Carnarvon Basin to flow oil.

The biggest discovery in the immediate area is the undeveloped Stag field, and there are several offshore wells that targeted the M.australis Sandstone on the Enderby Terrace that encountered significant oil shows, such as Altostratus-1 and Chamois-1, however, it is not known if the sandstone is present in proximity to the Lambert Shelf.

L14-3's best and closest well penetration is Fortescue-1, drilled by WAPET to the south east in the late 1960s, finding both oil and gas shows.

In terms of L15-4, WMC's 1992 Dill-1 and Command Petroleum's 1993 Santa Cruz-1 encountered significant oil shows in Lower Cretaceous sandstones.

Santa Cruz-1 was drilled to test the Birdrong Sandstone, with Upper Permian sandstones as a secondary objective, but is now recognised as an invalid test and may not have tested a valid structure.

Dill 1 was drilled 10km west of Santa Cruz-1 and did not find closure at the primary objective Barrow Group. Moderate hydrocarbon shows were observed throughout the Lower Cretaceous, Jurassic and Permian sections. This well also probably failed to test a valid trap.

The widely targeted Barrow Group may unconformably overlie tilted Triassic or Permian blocks, with the Birdrong Sandstone, the Mardie Greensand and the M.australis Sandstone as additional targets. The Barrow Group appears to be condensed in the area.

Santos' Bricklanding-1, the most recent well, drilled in 2006, was a duster with some poor gas shows in the Jurassic.

The primary target in most wells close to the area was the Lower Cretaceous sandstones, with Triassic or Permian strata as secondary targets.

The block is immediately south of Oil Basins' small undeveloped Nasutus and Cyrano fields.

Onshore in the Canning Basin L14-2 has been the focus of exploration for decades.

Shell once operated the permit and defined the large Cetus prospect, which was drilled a decade ago by private wildcatter Kingsway Oil as Sally May-1.

Billion barrel upside was described for a suprasalt play in the Elsa Sandstone, analogous to the south Oman oil province.

Subsalt oil shows could not be assessed due to rig limitations in Sally May-1, so in 2009 Kingsway drilled the Sally May-2 well, finding a lack of porosity in the target Nita Formation, where magnetoelluric studies had suggested, that porosity would be enhanced at the location.

The MT suggestion appears to be ill founded.

Hess Corporation took over Kingsway in 2012 and dropped L14-2 six months later.

The Nita is a highly promising subsalt play, which has been confirmed as oil-bearing in the promising Looma-1 well, just outside the block, which also indicated oil potential in the Willara and the Nambeet formations, with good quality reservoir noted in other wells.

Hydrocarbons were recovered from the subsalt Ordovician section by Shell in 1996's Looma-1, proving oil migration from the southern Canning Basin kitchen of the Kidson Sub-basin, providing a new exploration play.

Kingsway never assessed the suprasalt Elsa Sandstone.

The Sally May anticline may have over 300sq.km of closure and the two wells drilled so far have not fully evaluated the whole structure for conventional, tight gas and shale oil and gas resources.

Economic analysis completed by Kingsway indicated that an accumulation of just five million barrels could be capable of sustaining a moderate flow rate is likely to be economically attractive.

Even a small accumulation for any of the three objectives identified in the Sally May structure could be economically viable.

Applications for the areas will close in April.