Development of the method to remedy leakage from geological CO2 reservoir using CO2 reactive grout

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In order to remedy CO_2 leakage through pre-existing and/or induced fractures from storage reservoirs, we studied a concept to use an aqueous solution. The solution will have a sufficiently-low viscosity for passing through even small aperture, and it will not impact formation permeability as long as the solution is left as it is. When the solution encounters dissolved CO_2, precipitation will occur due to chemical reaction. As a result, the permeability will be reduced by filling the pores and fractures in the rocks with the precipitates. We demonstrated first this idea through laboratory experiments simulating subsurface condition at 1000 m deep, i. e. 10 MPa and 40 deg. C. The results show that the present method led to a 99 %permeability reduction in a glass-bead artificial rock even its initially-high permeability of few darcy. Such reduction of permeability was reproduced successfully by the non-isothermal reactive geochemical transport program TOUGHREACT. Based upon these success, the present method was applied by numerical modeling to a 2-D caprock-aquifer system under field physical and chemical conditions. The results show that the precipitates were produced and they filled up pores around outlet of the leakage path so sufficiently that the CO_2 migration was blocked, and the condition was confirmed stable over a long time.