High-temperature CO2 mineralisation in basaltic rocks: Inconsistencies between laboratory experiments and numerical modelling

EGU General Assembly 2024,, Vienna, Avusturya, 14 - 19 Nisan 2024, ss.1-2

The Nesjavellir high temperature geothermal reservoir, located in southwest Iceland, was one of

the test sites for the 'Geothermal Emission Control' (GECO) project. The project involves the

reinjection of exhaust gases from geothermal power plants into the subsurface for permanent

storage. Numerical modelling and field data from the nearby CarbFix2 storage site at Hellisheiði

indicate that even at high temperatures (< 280°C), large quantities of CO2 can be mineralised. To

complement these data, we investigated the potential for CO2 sequestration in the Nesjavellir

reservoir by conducting a 260 °C batch reaction experiment using a basaltic drill core sample and

effluent water from the Nesjavellir injection well. We also simulated the experiment using the

PHREEQC geochemical modelling program and observed significant inconsistencies between the

modelled and experimental results. The experiment produced a secondary mineral assemblage

dominated by zeolites, chlorites and anhydrite, with no carbonates observed. In contrast, the

model predicted the formation of calcite, which did not occur during the experiment. This

discrepancy is due to the model's inability to handle solid solutions and non-ideal phases

adequately. During the experiment, Ca was primarily incorporated into anhydrite and a Na-Cazeolite,

which resembles a solid solution of wairakite and analcime. However, the model did not

consider this phase, which resulted in Ca being incorporated into calcite instead of zeolite.