Re-evaluating the Stratigraphy of the Polda Basin: Implications for Underground Hydrogen Storage in Onshore Salt Caverns

The Polda Basin is a Neoproterozoic to Jurassic sedimentary basin, extending from the Great Australian Bight to the central Eyre Peninsula, South Australia. There has been renewed interest in the Polda Basin for its underground gas storage potential within salt caverns, given that Mercury-1 encountered >1200m of massive halite within Neoproterozoic red beds in the central offshore basin. Following this discovery, Kilroo-1A (CRA83-KD1A) was drilled onshore to explore for potash and proved the presence of equivalent redbeds in the eastern sub-basin, however no evaporites were intersected other than minor anhydrite veining. Prior to the discovery of the Neoproterozoic section in 1982, Pre-Cambrian redbed intersections onshore were referred to as Mount Wedge Grits, Corunna Conglomerate or Blue Range Beds, based on regional geology and outcropping strata at the basin margins. To assess the prospectivity for salt onshore, it is necessary to understand whether the onshore sub-basins contain sediments of a similar age in an environment favourable for evaporite deposition. The Colton-1 stratigraphic hole was drilled on the western Eyre in 1977, prior to the discovery of the salt-bearing Kilroo Fm, and reached total depth at 124mMD in similar redbed sediments. A key question is whether Colton-1 intersected the equivalent Kilroo Fm or the underlying Mesoproterozoic Blue Range Beds. If the latter, then the Neoproterozoic section is likely absent along the west coast, rendering it unprospective for salt. However, if Colton-1 bottomed in Kilroo Fm, then the prospective salt-bearing section could be present below the well. To answer this question and evaluate the prospectivity for salt onshore, a complete review of all available data and literature was undertaken and distilled into a regional cross section and modelled gravity profile spanning the length of the basin. This paper summarises several new insights into the basin stratigraphy and highlights the value of taking a multidisciplinary approach in applying new technology to legacy data.