Southern Carnarvon Basin

Panorama of the Peedamullah Shelf region, Southern Carnarvon Basin
Panorama of the Peedamullah Shelf region, Southern Carnarvon Basin

The onshore, primarily Paleozoic, Southern Carnarvon Basin has seen minimal exploration compared to the adjoining Perth and Northern Carnarvon basins. The Southern Carnarvon extends west from the Precambrian shield to the Mesozoic offshore Perth and Northern Carnarvon basins, and covers approximately 200,000 km2.

The basin is readily accessible from the North West Coastal Highway, and the Dampier to Bunbury gas pipeline runs through its eastern portion. In addition, large pastoral leases provide a network of roads and tracks, although these may close briefly after heavy rain.

Geological setting

The northerly elongate Southern Carnarvon Basin is composed of two principal structural elements: the Gascoyne Platform to the west, and the Merlinleigh and Byro Sub-basins to the east. The Gascoyne Platform contains gently folded Ordovician to Devonian strata, unconformably overlain by a veneer of Mesozoic and younger rocks.

In comparison, the Merlinleigh and Byro Sub-basins are characterised by a thick Upper Carboniferous to Permian section, underlain by a Lower Carboniferous–Devonian section, and unconformably overlain by a veneer of Cretaceous and younger rocks. The Paleozoic section is up to 7 km thick and is covered by Triassic rocks in the North. Northerly- and northwesterly-trending faults are also present.

Exploration history

Petroleum exploration commenced in the Southern Carnarvon Basin in the 1930s, after WG Woolnough first drew attention to the prospectivity of the Wooramel River area, and when hydrocarbon shows were encountered in shallow water bores in the northern part of the region. WAPET was the first company with serious exploration programs in the 1950s and 1960s, following its oil discovery at Rough Range.

After early exploration near Rough Range and other onshore coastal anticlines proved noncommercial, the main exploration activity moved north to the offshore Northern Carnarvon Basin. As of September 2014, 105 onshore (including 57 stratigraphic tests) and five offshore wells are drilled in the Southern Carnarvon Basin. No fields or accumulations have yet been discovered.

Petroleum prospectivity

The northernmost part of the Southern Carnarvon Basin is characterised by three large Cenozoic anticlines: the Rough Range, Giralia, and Marrilla Anticlines. Several smaller anticlines of the same age are exposed along the eastern and western shores of Lake MacLeod, in the central part of the basin, and similar anticlines underlie the peninsulas and islands of the Shark Bay region.

There are only a few valid tests for hydrocarbon plays in the region. Lower Cretaceous sandstone, which has excellent reservoir characteristics, is the main objective for oil exploration in the northern part of the basin, but seal adequacy and distance from effective source rocks are risks. Source rocks are present in Lower Permian, Upper Devonian, and Silurian strata (Larapintine 2 and 3, Transitional, and Gondwanan petroleum systems).

Read more about the petroleum prospectivity of the Southern Carnarvon Basin (page 48)