oa CO2-water-rock Reactions and Metal Mobilization: A CO2 Storage Demonstration Site in the Surat Basin

Demonstration scale CO2 geological storage has been proposed in the lower Precipice Sandstone, Surat Basin, Australia. The Evergreen Formation is the overlying seal (cap-rock), and the Moolayember Formation of the Bowen Basin the underlying formation (bottom seal). CTSCo has drilled several wells for feasibility studies. The potential for CO2-water-rock reactions to release metals to low salinity groundwater was a potential risk since the site is within the Great Artesian Basin. Metals were hosted in several minerals in the West Wandoan 1 well rock cores, with total concentrations higher in the Moolayember Formation and reservoir mudstones, than in the reservoir sandstones. Drill cores were reacted with supercritical CO2 or impure CO2-SO2-NO-O2 at in situ conditions. Minerals including calcite, ankerite, siderite, Fe-rich chlorite, and sulphides reacted. Dissolved Ca, Mn, Zn, Rb, etc. were released at variable concentrations dependant on the rock mineral content and gas stream. Fe and Pb generally increased initially, then decreased as Fe-oxyhydroxide minerals precipitated especially in the presence of O2. Carbonates were the main sources of metals as they dissolved more readily, with some release from ion exchange/desorption. Ultimately, a reactive transport model built from the data predicted that water quality impacts were restricted to the CO2 plume.