抄録
CCS (Carbon dioxide Capture and Storage) projects have been focused on as one of state-of-art technologies to prevent the CO2 emission in the atmosphere. In a project, the CO2 collected from factories is injected into the geological reservoir at deep underground through well and stored in the reservoir. It is expected that the well will have gradual degradations due to high temperature, high pressure and high concentration CO2 at deep underground. The process of the degradations should be investigated to prevent from leaking the CO2 through the well. In this study, the variation of pore structure and air permeability by the carbonation of the hardened cement paste exposed to the supercritical CO2 under water, salt water and sealed condition was examined focusing on the carbonation progress. The pore structure of small sample (diameter 4mm and height 4 mm) became denser at 1 day of exposure all cases because of the precipitation of CaCO3 in capillary pores while the carbonation of C-S-H occurred at 7 days to make pores coarse in the case of supercritical CO2 in water. It was experimentally found that the slight carbonation makes pores denser and leads to the reduction of the air permeability. The hardened cement paste using oil well cement with fly ash had denser pore structure to make permeability smaller than that using only oil well cement. It is attributed to Pozzolanic reaction of fly ash at high temperature. Thus, it was suggested that fly ash has a potential to apply to the CCS well from a view point of the prevention of CO2 gas leakage.
