Well-log-constrained porosity and permeability distribution in the Springbok Sandstone, Surat Basin, Australia

The Late Jurassic Springbok Sandstone in the Surat Basin, Australia, is highly heterogeneous in terms of lithology and hydrogeological properties. This heterogeneity is poorly defined in well logs, due, in part, to clay phases that do not exhibit a prominent gamma ray signature. The resulting uncertainties in the hydrogeological properties are propagated to uncertainties in the groundwater models of the Springbok Sandstone. Further, only a small amount of porosity and permeability data are publicly available and the discussion of petrophysical models for the Springbok Sandstone in the peer-reviewed literature has been limited. At the same time, accurately predicting the potential groundwater impact due to coal seam gas production from the underlying Walloon Subgroup is of significant societal and economic importance. This paper presents new porosity and permeability data from more than 50 core samples from the Springbok Sandstone alongside a review of existing data. Based on this dataset and wireline data from five study wells, a new petrophysical model for the formation is proposed. The results show that (1) the Springbok Sandstone is highly variable in terms of hydrogeological parameters, (2) this variability can be captured with a petrophysical model that draws on a full log suite (i.e. triple-combo) and (3) electrofacies classifications based on gamma-ray and bulk-density log cut-offs do not reflect this variability. This improved understanding of the Springbok Sandstone will contribute to best practice management of the water and hydrocarbon resources in the Great Artesian Basin.