Supplementary rock and water characterisation data

Supplementary rock and water characterisation data for a journal paper. Aquifer thermal energy storage generally involves storing intermittent renewable energy by injecting heated water subsurface into aquifers. Hot water – rock reactions may be induced depending on the rock formation composition. These could impact water quality changes if the water accidentally migrates, leaks or is released at surface. The associated dissolution- precipitation reactions may change rock properties, swell clays lowering permeability, or scale and clog pipes. Five drill core rock types from Australia were characterised and reacted; a coal seam gas reservoir interburden, calcite cemented reservoir sandstone, aquifer sandstone, mudstone caprock and marine oil shale. Dissolved element release was variable with potential elements of concern such as U, Mo, Zn, mainly released from marine oil shale. Elements such as Pb and As were released at relatively higher concentrations from CSG interburden and mudstone caprock reactions, however, dissolved concentrations remained generally low. Several REE were released at relatively high concentrations from caprock mudstone. Changes to stable isotopes of water and dissolved inorganic carbon along with 87Sr/86Sr were tested as potential reaction tracers, with dissolved 87Sr/86Sr approaching rock signatures. Mineral precipitation included calcite, Fe-(Cr)-oxides and clays with some clay fines movement. Dissolved element concentrations increased in reactions of calcite cemented sandstone and shale on cooling from additional calcite dissolution. The sandstones were geochemically more suitable for storage. Future work should include assessing permeability and rock strength changes. These reactions are also relevant to radioactive waste storage that generates heat in the subsurface.