SA/NT branch talk

Sharon Tiainen (left) and Paul Strong (right), receive vote of thanks from Rob Kirk (centre) for their stimulating SA/NT branch luncheon talk

“New Geological Studies Leading to 2025 Acreage Release in the Polda and Otway Basins, SA” The July 31 meeting was attended by 35 participants

The Polda Basin is a 10,000 km2 Neoproterozoic to Jurassic basin covering the central western portion of the Eyre Peninsula of South Australia and extends westwards into the Great Australian Bight. The basin is only lightly explored, with the last significant hydrocarbon exploration occurring in the offshore Polda Basin in the late 1970s/early 1980s, with no reported hydrocarbon shows except for a relatively minor gas show of 40 ppm methane in Mercury 1. However, source rock studies in the Jurassic section indicate the presence of immature, relatively high TOC and excellent generative potential for both oil and gas from carbonaceous claystone and coal. Recent work by the GSSA (Tiainen, 2025) indicates the presence of a potential source rock from the underlying Neoproterozoic Kilroo Formation, with oil staining identified in the permeable reservoir intervals in the Polda Formation in the onshore mineral drillhole Kilroo 1A. In addition, recent work conducted at the University of Adelaide suggests that there may be potential for a natural hydrogen accumulation within the onshore Polda Basin (Rumi Daruso 2023, shown in Margiono et al. 2024).

Following a recent acreage relinquishment, one new Regulated Substances Exploration Licence (RSEL) in the Polda Basin is being offered as acreage release block PO2025 RSEL-A by the South Australian Government for competitive work program bidding.

The Otway Basin is one of the best known and most actively explored of the series of Mesozoic rift basins that span the southern coastline of Australia, formed following rifting between the Antarctic and Australian plates. Over the last 2 years DEM has conducted studies over most of the onshore Otway Basin in South Australia, with results suggesting that significant hydrocarbons have been generated and expelled in a number of structural troughs in the region, and that suitable reservoir fairways and new play types are now better defined than previously.

Following a recent acreage relinquishment, five new regulated substances exploration licences (RSELs), three gas storage exploration licences (GSELs) and one new geothermal exploration licence (GEL) in the Otway Basin are being offered by the South Australian Government based on work program bidding. A key motivation for the acreage release is the looming shortfall in energy supply in the southeast Australian market. The South Australian onshore Otway Basin is in a strategic location for natural gas exploration and gas storage.

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