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.
