CO2 Solubility at High Pressures: Understanding Immobilization Techniques for Carbon Sequestration

The injection of fossil fuel power plant emissions into saline aquifers is a viable option for carbon sequestration. CO2 is injected as a positively buoyant supercritical fluid that, over time, dissolves into the connate brine and interacts with the host rock. The amount of CO2 that can be sequestered safely is poorly understood, due in part to the interaction of the plume with the brine and host rock. Established models suggest that in the long term CO2 is mineralized and trapped in the formation as a solid. However, the models also show that in the short term, CO2 is trapped as a soluble species or is free and buoyant and has the potential to migrate upward. Typical subsurface brines that are suitable for CO2 sequestration have pressures of over 12 MPa, up to 30% salinity by weight and temperatures above 35°C. The potential for CO2 to dissolve in brines is directly proportional to pressure and inversely proportional to salinity and temperature. Therefore, understanding the changes in solubility of CO2 with pressure, temperature, brine composition and salinity is imperative to making carbon sequestration safe and reliable. CO2 solubility in brine was measured at pressures up to 1500 psi, salinities up to 6 molal NaCl and between 35° and 75°. Power plant emissions also contain SO2, which is costly to separate from CO2. Preliminary results of the co-solubility of CO2-SO2 in brine solutions will also be presented.