CARBON DIOXIDE SOLUBILITY IN BRINES FOR THE PURPOSE OF STORAGE IN GEOLOGIC FORMATIONS

Brine composition is highly variable in formations suitable for long-term CO₂ storage. The Rose Run Formation in the Appalachian Basin has one of the highest concentrations of dissolved solids in the formations currently being studied for this purpose. Therefore, knowing the storage capacity of CO₂ in this formation brine would further the understanding of the maximum amount of CO₂ that can be safely stored in any site of interest. Dissolving CO₂ in formation brines has been shown to be one of the most important solutions for the long-term storage of the greenhouse gas. Once CO₂ dissolves into the brine, it forms a negatively buoyant plume that is unlikely to migrate back to the atmosphere or to contaminate any resources used by people. However, the solubility of CO₂ in solutions found in these storage locations is largely unknown. The addition of SO₂, a co-contaminant in fossil fuel power plant waste streams, could be co-injected into geologic formations for safe long-term storage. The addition of this gas would decrease the density and pH of the brine, increasing the potential for greater dissolution of the surrounding rock. For this study, the solubility of CO₂ was determined in solutions of up to 4 m of the most important salts found in saline formations, including NaCl, KCl, CaCl₂ and MgCl₂, at pressures up to 14 MPa as well as in a simulated Rose Run Formation brine and dissolved with SO₂. These data compare well to both the limited data and models in the literature. Both the type of salt and the salinity of the solution affect the solubility of CO₂. The solubility decreases with increasing composition of any salt, most significantly with the addition of NaCl.