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Akira Ueda, Kyoto University (Japan)
Yoshihiro Kuroda, Kyoto University (Japan)
Yasuhiro Yamada, Kyoto University (Japan)
Ziqiu Xue, Kyoto University (Japan)
Toshifumi Matsuoka, Kyoto University (Japan)
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Underground disposal of CO2 have been proceed in the world, where the temperature of the CO2 reservoir is less than 100 °C. In this condition, the injected supercritical CO2 and dissolved CO2 in brines are thought to be stable due to slow rates of chemical reaction with reservoir rocks. Experimental and theoretical consideration of the chemical reaction of CO2 saturated water and rocks have been reported. For example, the following reaction can proceed to the right side at high temperature;
CaAl2Si2O8 (plagioclase) + H+ + HCO3- + H2O = CaCO3 (calcite) + Al2Si2O5(OH)4 (kaolinite).
The reaction moves towards the right side at higher temperature, while at the same time calcite can be deposited more easily because the solubility of calcite decreases with increasing temperature. The calcite and kaolinite (smectite)-rich formation that is produced acts as a cap rock to the geothermal and saline aquifer reservoirs. These considerations, together with the increasing reaction rates as temperatures are elevated and CO2 fixation in solid carbonate minerals, suggests that CO2 sequestration by injection into relatively high temperature fields could be practicable.
Experiments on CO2-plagioclase-rock interaction at room to hydrothermal temperatures have been performed to investigate dissolution and precipitation phenomena, including Ca extraction from rocks, that might occur during CO2 sequestration into relatively high temeprature fields. The anorthite, labradorite and granodiorites from the Ogachi hot/dry rock field, were reacted in distilled water with and without CO2 being present. The results indicate that Ca concentration in the solutions quickly increase within 2 days and become constant for 30 days. The concentration of Ca in the solutions reacted with CO2 is 50mg/L higher than those without CO2 (with N2 gas).
These preliminary results indicate that Ca can be released from rocks (silicates) easily and might be removed as CaCO3 during CO2 sequestration into high temperature conditions such as geothermal fields. The experimental data will be also discussed with the results of CO2 injection tests at the Ogachi site performed in 2007.
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