Application of MRI in the Measurement of Two-Phase Flow of Supercritical CO2 and Water in Porous Rocks

Storage of CO2 in geological formations is one way to mitigate the greenhouse gas emission. Immiscible two-phase flow of CO2 and water is affected by viscosity, buoyancy, and interfacial tension. Therefore understanding CO2 migration in porous rocks will improve the ability to predict long-term behavior, including changes in trap mechanisms such as residual gas and solubility trapping. This article describes experimental research on two-phase flow of supercritical CO2 and water in porous rocks under sequestration conditions. We used magnetic resonance imaging to directly visualize the distribution of supercritical CO2 injected into porous rocks containing water, under conditions similar to those at 800-m depth in an aquifer. A special core analysis method has been applied to in situ saturation data to estimate directly the effect of viscosity, buoyancy, and capillary pressure on CO2 migration. Next, we developed a noninvasive nuclear magnetic resonance (NMR) technique to measure the amount of CO2 dissolved in water in porous rock. The relaxation time of the NMR signal is shortened by the porous material surfaces and CO2 dissolution. Continuous monitoring of the relaxation time at the same position can help to monitor dissolved CO2 in underground water in a noninvasive manner.