The Simpson Basin extends over ~57 500 km² in South Australia and the Northern Territory (over half lies in South Australia). It is a circular, poorly defined depression with one major depocentre, the Poolowanna Trough. The basin overlies Palaeozoic and older basins and is overlain by the Eromanga Basin (Jurassic to Cretaceous).

Petroleum exploration commenced in the 1950s when licences covering the Cooper and Eromanga basins were first acquired by Santos, who went against conventional wisdom that commercial accumulations of oil would not be found in Mesozoic formations within the Great Artesian Basin.

Initial exploration involved surface mapping, stratigraphic drilling, aerial surveys, gravity and aeromagnetic surveys and seismic. The first petroleum well was drilled in 1959 and Cooper Basin gas was discovered in 1963.

A second round of activity occurred from 1969–79, when five seismic surveys were carried out and one well was drilled. A seismic survey in 1971 revealed an eastward thickening sediment package between the eastern Pedirka Basin and the Eromanga Basin. The postulated Triassic age for these sediments was confirmed when Poolowanna 1 recovered oil from this sequence in 1977. The interval was subsequently defined as the Simpson Basin

Exploration activity intensified in the Poolowanna Trough/Pedirka Basin area in the 1980s in response to the Poolowanna discovery. Six petroleum wells have penetrated the Simpson Basin and over 11 000 km of seismic acquired in the 1970s and 1980s by Delhi–Santos.

Seismic reinterpretation by Santos indicated that five of the previously drilled wells in the region were not valid structural tests being outside closure at all objectives. Of the 1985 wells, Oolarinna 1 had no independent fault closure and Glen Joyce 1 had little closure.

It should be noted that no wells have been drilled in the South Australian sector since the 1980s, although Central Petroleum drilled Blamore 1 and Simpson 1 in the Northern Territory in 2008. Exploration in the area would benefit from current ideas on the geology of the petroleum systems in the Cooper Basin region and modern technology and interpretation techniques.

Hydrocarbon shows have been recorded in most wells within the Pedirka Basin region. However, oil and gas has been recovered from only 2 wells, the Poolowanna and Peera Peera Formations in Poolowanna 1, and the Poolowanna Formation in Poolowanna 3.

The classification scheme used by Geoscience Australia has been used to determine the type of show present in a formation in the tables below.

Hydrocarbon shows and flow rates in South Australian wells in the Poolowanna Trough/Simpson Basin/Pedirka Basin region:

Hydrocarbon shows in Northern Territory wells in the Poolowanna Trough/Simpson Basin/Pedirka Basin region:

See Simpson Basin figure 1

The Simpson Basin contains ?Early to Middle Triassic Walkandi Formation overlain conformably by Late Triassic Peera Peera Formation. Walkandi Formation is restricted to the Poolowanna Trough depocentre. The Peera Peera Formation extends westwards and onlaps the Dalhousie–McDills Ridge and eastwards where it onlaps the Birdsville Track Ridge.

The oxidised nature of the Walkandi Formation redbeds downgrades source potential. However, the overlying Peera Peera Formation is rich in organic matter (TOC up to 5%) and should be oil mature in the Poolowanna Trough. The Peera Peera Formation is considered to be gas-prone with modest oil yields.

Limited drilling indicates that sandstone interbeds in the Walkandi Formation are fine grained, with low porosity and permeability. The Peera Peera Formation also suffers from laterally variable, poor quality reservoirs (maximum measured porosity 7.8%). Reservoir quality is thought to improve updip from the Poolowanna Trough.

Seals consist of intraformational siltstone and shale of the Walkandi and Peera Peera formations.

Potential trapping mechanisms are dominantly structural (faulted anticlines).

There is no estimate of undiscovered resources.

The Simpson Basin is overlain by the Munga-Thirri–Simpson Desert Regional Reserve where exploration is permitted (South Australian Reserved Land figure), and the Munga Thirri–Simpson Desert Conservation Park where exploration is not permitted.

See Simpson Basin figure 1

Figure 4 above shows the licence status at the time of publication. For more information on current licences please refer to Holders of Petroleum and Geothermal Tenements in SA information sheet

Cotton TB, Scardigno MF and Hibburt JE eds, 2006. The petroleum geology of South Australia. Vol. 2: Eromanga Basin. 2nd edn. South Australia. Department of Primary Industries and Resources. Petroleum Geology of South Australia Series.

Moore PS, 1986. Jurassic and Triassic stratigraphy and hydrocarbon potential of the Poolowanna Trough (Simpson Desert Region), northern South Australia. In: Gravestock DI Moore PS and Pitt GM eds, Contributions to the geology and hydrocarbon potential of the Eromanga Basin. Geological Society of Australia. Special Publication, 12:39-51.

Powis GD, 1989. Revision of Triassic stratigraphy at the Cooper Basin to Eromanga Basin transition. In: O’Neil BJ ed, The Cooper and Eromanga basins, Australia. Proceedings of the Cooper and Eromanga Basins Conference, Adelaide, 1989. Petroleum Exploration Society of Australia, Society of Petroleum Engineers, Australian Society of Exploration Geophysicists (SA Branches), pp.265-277.

Wiltshire MJ, 1989. Mesozoic stratigraphy and palaeogeography, eastern Australia. In: O’Neil BJ ed, The Cooper and Eromanga basins, Australia. Proceedings of the Cooper and Eromanga Basins Conference, Adelaide, 1989. Petroleum Exploration Society of Australia, Society of Petroleum Engineers, Australian Society of Exploration Geophysicists (SA Branches), pp.279-291.

See additional references in the Peera Peera Formation play analysis.