Capillary trapping of supercritical CO2in porous media at the pore scale

Abstract

Carbon dioxide capture and storage in geological formations is recognized as a promising method for decoupling fossil fuel use and carbon emissions. Carbon dioxide injected into geological formations is expected to be trapped by several mechanisms against buoyancy. In this paper, we focused on capillary rapping. Trapped bubbles in packed beds of glass beads were visualized by means of micro-focused X-ray CT at pore scale for supercritical CO2 and water systems at reservoir condition and for nitrogen and water systems at laboratory room condition. When the diameter of glass beads is the same, distribution of volume of trapped bubbles is similar for each condition. At the pressure of 8.5MPa and the temperature of 45oC, which corresponds to just above a critical point, the morphology of the interface between the supercritical CO2 and water suggests that CO2 is non-wetting to glass beads. Residual gas saturation increases with a decrease in a diameter of glass beads, because the capillary pressure is higher with respect to buoyancy. Residual gas saturation can be expressed as a function of the reverse Bond number for each condition. Distribution of trapped bubble volume is identical with each other for each condition at same diameter of glass beads. The large trapped bubbles contribute to the residual gas saturation.