Experimental studies of CO₂-rock interaction at elevated temperatures under hydrothermal conditions

Experiments on CO₂-water-rock interaction at hydrothermal temperatures have been performed to investigate dissolution and precipitation phenomena, including Ca extraction from rocks that might occur during CO₂ sequestration into geothermal fields. Distilled water samples were exposed to a CO₂ atmosphere at a temperature of 25°C and pressures up to 6 MPa. The resulting solutions were then reacted with granodiorite samples from the Ogachi hot/dry rock field and labradorite, at 200°C and 120°C respectively. The calcium concentrations in the solutions that had reacted with CO₂ were twice those with N₂ instead of CO₂. Combined with the results of thermodynamic calculations, these observations indicate that calcium can be released from rocks (silicates) easily and might be removed as CaCO₃ and/or CaSO₄ during CO₂ sequestration into geothermal fields.