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 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.