Hydrogeochemical modeling of mineral alterations following CO2 injection

Abstract Alterations of the mineral phase of deep reservoirs are desired as a process for carbon capture and storage, driven by changes in fluid composition due to CO2 injection. Underlying concepts for hydrogeochemical modeling are implemented in the codes PHREEQC and MIN3P, adapted to cope with pressures and temperatures in deep reservoirs with up to 300 °C and 1000 atm. Simulations were performed using field data from the Heletz, pilot CO2 injection site (Israel), located at the edge of a decommissioned oil field in a sandstone formation, showing a shift of saturation index (SI) and dissolution/precipitation reactions of silicates and carbonates subsequent to injection of CO2. Alterations of the mineral phase with time were largest in the sequence Ankerite > Dolomite > Calcite > Magnesite, and for the mineral Dawsonite during early stages when only Na+ is present in high ionic concentrations. The uncertainty of mineral saturation, a consequence of the variability of water chemical composition and the database records, was investigated by principal component analysis and sensitivity coefficients. A large variability in the occurrence of Dolomite can be explained by salinity variations and the inverse dependency of total amount of carbon mineralization between Pitzer and Debye-Huckel/Davies (D-H/D) based activity computation.