Experimental evaluation of chemical sequestration of carbon dioxide in deep saline formations

Deep saline formations are considered to be among the largest and most widely available potential reservoirs for long-term to permanent storage of CO2. However, before deep well injection of CO2 can be considered at terrestrial sites, several prerequisites must be completed, including detailed evaluations of geochemical issues. Because of the many geochemical processes involved, the feasibility of injection will be influenced by the specific chemical interactions that take place between a CO2-rich brine and the native rock. Also, because the characteristic time of the injection (e.g., 20 years) may be either faster or slower than some geochemical processes, the rate behavior of these processes needs to be well understood. This paper presents preliminary results of an ongoing experimental investigation of CO2-brine-rock interactions to answer questions concerning solid phase stability and reaction kinetics. In this study, reactions between a natural sandstone, synthetic brine, and supercritical phase CO2 were investigated. It was postulated that addition of CO2 and subsequent carbonation of the brine could either promote long-term storage by precipitation of carbonate minerals, or interfere with injectivity by reducing the permeability of the formation. Experiments are being conducted using both mineralogically pure samples and rock samples from the Mt. Simon formation in the Midwestern United States and Texas Gulf Coast region. The effects of pressure, temperature, time, and brine composition on mineral transformations are being investigated.