Geochemical modeling of CO2 injection and gypsum precipitation at the Ketzin CO2 storage site

Abstract Gypsum crystals are found at the well perforation of observation Ktzi 202 test site for CO 2 storage Ketzin, Germany. XRD analysis confirms pure gypsum. Fluid samples before and after injection analyzed. Geochemical modeling is conducted to identify mechanisms that lead gypsum formation. The carried out with PHREEQC Pitzer database due high salinity up 5 mol per kg water. Due their significantly higher reactivity compared other minerals like silicates, calcite, dolomite, magnesite, gypsum, anhydrite, halite considered as primary mineral phases matching observed brine compositions in our simulations. Calcite, close saturation injection. Dolomite shows highest mainly contributes buffering pH initially decreased contribution calcite pH-buffering only minor. anhydrite no geochemically active After injection, precipitation may occur by two mechanisms: (i) dissociation decreases activity water and, therefore, increases all (ii) dolomite dissolution releases Ca 2+ ions into solution shifts mass action increasing temperature but partial pressure. Our calculations show calcium sulfate a factor depth 2000 m when Ketzin pressure extrapolated. In general, constitutes potential clogging hazard during could negatively impact safe operation. presented example, this threat minor since total amount relatively small.