We present here a method to reduce the medium permeability along potential leakage paths of the CO2 storage reservoir at deep depth. This method employs a grout of aqueous solution, however, the leakage paths are plugged by not the grout itself but the products of the reaction between the aqueous solution and CO2. The aqueous solution will be injected into the fractures and rocks through boreholes. 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 CO2, a precipitation reaction will occur. As a result, the permeability will be reduced by the precipitation filling the pores and fractures in the rocks. This idea was demonstrated through laboratory experiments simulating subsurface condition at 1000m deep, i.e. 10MPa and 40°C, and using a silicate solution. In this case, the solution - CO2 reaction should produce the precipitation of amorphous silica. The results of laboratory experiments 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 by reactive transport simulation using 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. Then we considered typical two scenarios to remedy CO2 leakage from a reservoir. For the first scenario, the reactive grout of the silica solution is injected after the occurrence of CO2 leakage, and for the second scenario, the aquifer overlying the caprock has been filled with the reactive grout in advance of the occurrence of CO2 leakage. For both the scenarios, the silica precipitation were produced and they filled up pores around outlet of the leakage path so sufficiently that the CO2 migration was blocked, and the condition was confirmed stable over a long time.
ASJC Scopus subject areas
- Industrial and Manufacturing Engineering
- Management, Monitoring, Policy and Law