Effect of the Flow Rate on the Relative Permeability Curve in the CO₂ and Brine System for CO₂ Sequestration

The relative permeabilities of CO₂ and brine are important parameters that account for two-phase flow behavior, CO₂ saturation distribution, and injectivity. CO₂/brine relative permeability curves from the literature show low endpoint CO₂ permeability values and high residual brine saturation values. These are the most distinguishing aspects of the CO₂/brine relative permeability from oil/water and gas/oil. In this study, this aspect is investigated experimentally by employing a wide range of CO₂ injection flow rates. As a result, all the measurements align with previous studies, having low endpoint relative permeability and high residual brine saturation values. They have obvious relationships with the changes in CO₂ flow rates. As the CO₂ flow rate increases, the endpoint relative permeability increases, the residual brine saturation decreases, and they converge to specific values. These imply that a high CO₂ injection flow rate results in high displacement efficiency, but the improvement in efficiency decreases as the flow rate increases. The reasons are identified with the concept of the viscous and capillary forces, and their significance in the CO₂ injection into a reservoir is analyzed.