Multidimensional reactive transport modeling of CO₂ mineral sequestration in basalts at the Hellisheidi geothermal field, Iceland

Two and three-dimensional field scale reservoir models of CO₂ mineral sequestration in basalts were developed and calibrated against a large set of field data. Resulting principal hydrological properties are lateral and vertical intrinsic permeabilities of 300 and 1700×10^-15m², respectively, effective matrix porosity of 8.5% and a 25m/year estimate for regional groundwater flow velocity.Reactive chemistry was coupled to calibrated models and predictive mass transport and reactive transport simulations carried out for both a 1200-tonnes pilot CO₂ injection and a full-scale 400,000-tonnes CO₂ injection scenario. Reactive transport simulations of the pilot injection predict 100% CO₂ mineral capture within 10years and cumulative fixation per unit surface area of 5000tonnes/km². Corresponding values for the full-scale scenario are 80% CO₂ mineral capture after 100years and cumulative fixation of 35,000tonnes/km². CO₂ sequestration rate is predicted to range between 1200 and 22,000tonnes/year in both scenarios.The predictive value of mass transport simulations was found to be considerably lower than that of reactive transport simulations. Results from three-dimensional simulations were also in significantly better agreement with field observations than equivalent two-dimensional results.Despite only being indicative, it is concluded from this study that fresh basalts may comprise ideal geological CO₂ storage formations.