The geology and water chemistry of the Hellisheidi, SW-Iceland carbon storage site

► Chemistry of Hellisheidi rocks and groundwaters was studied prior to CO2 injection. ► The gas charged injection waters are acidic and thus reactive. ► The rocks will dissolve, increasing porosity near the vicinity of the injection well. ► Model calculations indicate formation of Ca-Mg-Fe-carbonate and dolomite at low pH. ► Upon further basalt dissolution and elevated pH, ankerite and calcite will form.