CO2 emissions potentially can be collected from point sources and injected into deep sandstone formations where they will be prevented from reaching the atmosphere. Once injected, the CO2 can be stored as a free supercritical phase, as dissolved aqueous phases, or as solid carbonate minerals. Free supercritical CO2 is subject to buoyancy forces that drive it toward the surface and thus is at risk of escape. CO2 (aq) and carbonate species dissolved in brine have a negative buoyancy, which reduces the risk of escape. Trapping the CO2 in immobile, solid carbonate minerals provides the safest, most long term storage. We are investigating the factors that control how much and how fast CO2 can be converted to dissolved or solid mineral forms for safe, long-term storage of CO2 in the deep subsurface.

 

Figure 1: The Rose Run Sandstone is a sandy layer in the middle of the Knox dolomite that lies at a suitable depth beneath eastern Ohio for injection of CO2 as a supercritical fluid. Large, coal-fired power plants, which are concentrated in eastern Ohio, are point sources of CO2 that potentially can be disposed of by injection into the Rose Run and other deep sandstone formations.

 

 

 

Figure 2: The Rose Run Sandstone is heterogeneous at multiple scales, consisting of interbedded sandstone and carbonate layers. Glauconite layers and sandstone layers with alkali feldpsars are likely to be important for trapping CO2 as carbonate minerals as a result of CO2-brine-mineral reactions.

 

Figure 3: Results of equilibrium geochemical modeling show that the carbonate minerals siderite and dawsonite are likely to be most important for trapping CO2, especially near the injection site where high CO2 fugacity will be encountered. As the CO2 disemminates other carbonate minerals become more significant for trapping CO2. Thus the rate of mineral trapping in carbonate phases relative to the rate of dissemination of CO2 is very important for predicting how much CO2 will be trapped as a solid immobile carbonate phase.

 

 

Figure 4: We designed and built inexpensive rocking tube reactors so that we could conduct long term CO2-brine-mineral reaction experiments.

 

Figure 5: Our far from equilibrium data show linear changes in concentration with time that can be used to calculated rates of mineral dissolution.

 

Figure 6: Over longer periods we can document the dissolution and precipitation of mineral phases. The albite has a swiss-cheese appearance due to dissolution, the finer grained mineral rosettes may be dawsonite.