Mineralogical characterisation of a potential reservoir system for CO2 sequestration in the Surat Basin

The Jurassic-aged Precipice Sandstone and Hutton Sandstone in the Surat Basin (Queensland) are potential targets for CO2 sequestration that exhibit considerably different mineralogies. Hyperspectral logging was complemented with petrographic studies to reveal core-scale mineralogical distributions. Scanning electron microscopy and X-ray diffraction analyses of the bulk rock composition and clay (<2m) fraction provided an adjunct to mineral identification. The Precipice Sandstone is interpreted to be geochemically poorly reactive with a clean, quartzose mineralogy dominated by quartz and kaolinitic clays. These clays coat grains and partially fill pores, having formed from the extensive leaching of unstable feldspars and lithics, and are commonly associated with Fe-oxide/hydroxide. The mineralogy of the Evergreen Formation is geochemically reactive and contains significant feldspar, smectite, chlorite, carbonate and kaolinite, and should therefore serve as an effective intraformational seal. Low permeability in the Evergreen Formation is attributed to extensive porosity loss following burial compaction, which is evident from the formation of pressure-dissolution features and a lithic-derived clay-rich pseudo matrix in several samples. The Hutton Sandstone is a heterogeneous potential reservoir, with geochemically reactive intervals containing smectite, chlorite and FeMnMgCa carbonates, in addition to feldspars and lithics. Variable clay matrix content, porosity and locally significant cementation within the Hutton Sandstone indicate a mineralogically heterogeneous unit that could have the capacity to buffer emplaced CO2. This potentially provides an additional vertical component of capture and storage to the potential reservoir system, in addition to the traditional regional seal provided by the Evergreen Formation.