An experimental study on CO2/water displacement in porous media using high-resolution Magnetic Resonance Imaging

Abstract

CO2/water displacement process in porous media under sequestration conditions was observed using high-resolution Magnetic Resonance Imaging (MRI) technique. The porous media was a packed bed filled with glass beads. Fast spin echo multi slice sequence (FSEM) was used to measure the distribution of CO2 and water in the porous media. For immiscible displacement experiments, three stages were obtained from the MR signal intensity profile. The CO2 channeling or fingering phenomena was obviously for the difference of permeability during the second stage. The final water residual saturation depended on permeability, and lower permeability always leads to larger final saturation. For miscible displacement, the displacement process was also divided into three stages from MR signal intensity profile. The MR signal intensity decreased gradually for the resolving of CO2 into water in the first stage. A piston-like miscible front moved uniformly from the top to the bottom of the FOV (field of view) during the second stage, and the MR signal intensity decreased sharply. The displacement efficiency in miscible displacement is larger than that in immiscible displacement process. It is clear that water displacement efficiency or average CO2 saturation depends on flow rate. With the CO2 flow rate increasing, the relatively uniform CO2 distribution and the uniform CO2 front occurred. Additionally, final water saturation decreased. With the core analysis methods, the CO2 velocities were obtained, which were applied to evaluate the capillary dispersion rate, viscous dominated fraction flow and gravity flow function. The capillary dispersion rate donated the effects of capillary, which was largest at water saturations of 0.6 and 0.7. At a high flow rate, the viscous force was dominated over the porous media. When at a low flow rate, the gravity force became important and played a positive role in downward displacements.