CO₂ sequestration into geothermal fields

This chapter evaluates a possibility to sequester CO₂ by the storage of a free CO₂ phase and by fixation in carbonate minerals in geothermal fields in Japan. In most Japanese geothermal fields, carbonate-rich formations are observed. Underground disposal of CO₂ has been preceded in the world, where the temperature of the CO₂ reservoir is less than 100°C. In this condition, the injected supercritical CO₂ is thought to be stable because of slow rates of chemical reaction with reservoir rocks. The characteristics of Ca extraction from rocks during reactions with CO2-charged water have been evaluated experimentally. A drill core from the Ogachi hot/dry rock field, Akita, Japan is sampled at a depth of 1061m (grained granodiorites). In this experiment, Ca can be released from both anhydrite and silicates such as plagioclase. To calculate the concentrations of Ca released from silicates, the observed Ca concentrations are adjusted on the basis of Ca/SO4 mole ratios in the solutions. These results indicate that Ca can be released easily from silicates and might be removed as CaSO4 and/or carbonate during CO₂ sequestration into geothermal fields. The comparison of the experimental results between one with CO₂ and the other without CO₂ showed that Ca is easily released by the CO₂ charged water.