HYDROCARBON POTENTIAL OF THE ARCKARINGA REGION, CENTRAL SOUTH AUSTRALIA

Abstract

The Arckaringa region is a large area which lies between the Officer Basin and the Peake and Denison Ranges in central South Australia. It includes sedimentary rocks of Jurassic-Cretaceous, Permo-Carboniferous and ?Cambrian ages. The thickest sequence of sediments (about 2000m) occurs in the Boorthanna Trough, located immediately to the west of the Peake and Denison Ranges. Cretaceous sediments of the Eromanga Basin form a veneer over much of the area. Oil shows at very shallow depths in immature sediments at Oodnadatta 1 raise speculations about the possibility of shallow generation of hydrocarbons in the Eromanga Basin. However, most of the petroleum exploration in the region has been aimed at delineating the underlying Permo-Carboniferous Arckaringa Basin sequence. The Arckaringa Basin is not a simple sedimentary depression but rather a series of peripheral depressions surrounding a central platform region. Unlike the Cooper and Pedirka Basins, it contains some marine sediment, suggesting the possibility of an oil-prone rather than a predominantly gas-prone province. Due to the thin nature of the sequence and its shallow depth of burial, most of the Arckaringa Basin is predicted to be immature for hydrocarbon generation in traditional terms. However, source-rock and vitrinite studies in the Boorthanna Trough indicate that the basal units are marginally mature to mature in this area. Early Cambrian carbonates are interpreted to extend southeastwards in an arc from Byilkaoora 1 in the Officer Basin, through the Boorthanna Trough, and onto the Stuart Shelf. In the Boorthanna Trough these carbonates are named the Cootanoorina Formation. They are of varied lithology and are associated with terrigenous clastics and minor evaporites. Vugular porosity occurs sporadically in the sequence, which may be thicker than 1000m in some of the deeper parts of the trough. Source-rock studies suggest that the sequence is immature to marginally mature in Weedina 1 and Cootanoorina 1.

It is emphasised that the Arckaringa region is largely unexplored for hydrocarbons, with only two wells drilled on structural targets in the entire area of about 60 000 sq km. This report presents source-rock and maturation data which suggest that the sequence is more mature than originally predicted, and that the deeper parts of the Boorthanna Trough may have a modest potential for oil, both in the basal Permo-Carboniferous and in the ?Cambrian Cootanoorina Formation. An active exploration programme has begun, with several hundred kilometres of seismic surveys planned for 1982.