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 × 10−15 m2, respectively, effective matrix porosity of 8.5% and a 25 m/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 10 years and cumulative fixation per unit surface area of 5000 tonnes/km2. Corresponding values for the full-scale scenario are 80% CO2 mineral capture after 100 years and cumulative fixation of 35,000 tonnes/km2. CO2 sequestration rate is predicted to range between 1200 and 22,000 tonnes/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.

► Development of field scale mass transport and reactive transport models.
► Calibration of permeability, effective matrix porosity and regional flow velocity.
► Less predictive value in mass transport models than reactive transport models.
► 3D models in significantly better agreement with field observations than 2D models.
► CO2 mineral sequestration in basalts predicted to be a viable option.