Pedirka Basin – Poolowanna Trough region.
The Energy Resources Division has released new play analysis of this under explored region in central Australia to stimulate hydrocarbon exploration. Intervals reviewed include the Jurassic–Cretaceous Algebuckina Formation and the Jurassic Poolowanna Formation of the Eromanga Basin, the Peera Peera Formation of the Triassic Simpson Basin, and the Permian Purni Formation of the Pedirka Basin. Results are detailed on the DEM website.
Pedirka Basin – Poolowanna Trough region covers around 100,000 km2, just over half of which is in South Australia and most of the remainder in the Northern Territory.
Exploration in the region commenced in 1959 and the first wells were drilled in the 1960s. Oil was discovered in the Poolowanna Trough in 1977 with flows of oil from Early Jurassic and Triassic sediments in Poolowanna 1, although these were uneconomic to produce due to the small volumes. Exploration activity intensified in the 1980s; however, no further discoveries were made even though many of the wells encountered hydrocarbon shows.
A ‘play’ can be defined as a trend or family of geologically related leads, prospects, and possibly producing fields, with primary elements of similar geological history of hydrocarbon charge, reservoir–seal pairs and trap controls on their occurrence. They are typically defined by stratigraphic name or age, with plays generally separated by a regionally significant master seal. Play analysis, or play-based exploration, is simply a method to build and leverage an understanding of geological basins and petroleum systems. The methodology incorporates the integration of many tools such as seismic data, well log and palynological data, structural analysis and geochemistry to define a series of play maps that can be used to focus exploration strategy and improve prospect chance assessment. Fundamentally, this process is not static, with iterative feedback required following new information from drilling, seismic data, studies etc. to update the knowledge base and keep it evergreen.
As an example, Figure 1 shows the play elements for the Poolowanna Formation in the Pedirka Basin – Poolowanna Trough region, being the limits of the Poolowanna Formation reservoirs, the sealing intervals for the reservoirs, and the migration extents for the 3 potential source rock intervals that have probably generated hydrocarbons in the region. The combination of these limits where all 3 elements are present is shown in Figure 2, indicating the approximate extent of the play, outside of which in theory there is no chance that the play will be found. However, as with all models, the limits are only as good as the data used to construct them. Seismic coverage in this region is relatively sparse compared to the Cooper Basin and the well data is also quite widely spaced, so there may be some variability on the exact location of the limits shown in Figure 1.
Figure 1 Play elements for the Jurassic Poolowanna Formation in the Pedirka Basin –Poolowanna Trough region.
Figure 2 also shows the present day undrilled structural closures within the Poolowanna Formation, some of which may contain hydrocarbons. However, note the coverage of 2D seismic data within the region is limited and so in reality the structures shown may be quite different to the way they have been mapped.
Figure 2 Approximate extent of the Poolowanna Formation play with undrilled structural closures shown in green.
Regional structural reactivation occurred in the Miocene epoch around 10 million years ago, breaching some of the closures. This occurred at the Poolowanna Field, which recovered only 9½ barrels of oil, with the total volume of oil estimated in the field being too small to be economically producible. Therefore, exploration is required of more subtle structures not affected by the reactivation in the Miocene.
The South Australian sector of the Pedirka Basin – Poolowanna Trough region is currently covered by several petroleum exploration licences and licence applications. Petroleum and mineral exploration are not permitted within the Munga-Thirri–Simpson Desert National Park.
More about the plays:
- Poolowanna Formation, Eromanga Basin
- Peera Peera Formation, Simpson Basin
- Purni Formation, Pedirka Basin
The Eromanga Basin Algebuckina Formation play map will be published soon.
– Paul Strong, December 2021
