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The basin overlies Palaeozoic and older basins and is overlain by the Eromanga Basin (Jurassic to Cretaceous).
|Area in South Australia||50 000 km2 (19 300 sq miles)|
|Depth to target zone||2000-2600m|
|Thickness||Up to 300m|
|Hydrocarbon shows||Peera Peera Formation (shows in 5 wells)|
|First commercial discovery||None|
|Undiscovered resources (50%)||Not determined|
|Reservoirs||Meandering fluvial sandstone|
|Regional structure||N-S faulted anticlines in sag basin|
|Seals||Lacustrine and overbank sediments|
|Source rocks||Underlying Pedrika Basin siltstone and shale; Peera Peera Formation siltstone and shale|
|Number of wells||6|
Seismic line km
The Simpson Basin extends over ~100 000 km2 in South Australia and the Northern Territory (approximately 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).
During the Triassic, the western Pedirka Basin area remained elevated and was eroded, while the eastern portion subsided to form a depocentre, the Poolowanna Trough. Regional uplift and erosion terminated deposition in the Simpson Basin at the end of the Early to Middle Triassic. The main episode of structuring occurred in the Early Tertiary, when E–W compression produced major meridional faulted anticlines.
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. Six petroleum wells have penetrated the basin and over 11 000 km of seismic acquired in the 1970s and 1980s by Delhi–Santos. The area was relinquished in 1989–90. A number of licence applications are current.
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.
Walkandi Formation consists of interbedded shale, siltstone and minor sandstone redbeds deposited in a shallow ephemeral lacustrine environment. The unit correlates with the Tinchoo Formation of the Cooper Basin to the east. Peera Peera Formation consists of grey shale and siltstone at the base with minor thin sandstone and coal, a fining upward sandy middle unit and a black, silty highly carbonaceous shale at the top — reflecting deposition on a floodplain crossed by meandering fluvial streams with lacustrine development. It is correlated with the Cuddapan Formation of the Cooper Basin region.
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.
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.