Pore-Scale Displacement Experiments Using Microfluidic Device to Investigate Fingering Mechanisms Using Both CO2 and N2: Implications for EOR and CO2 Geo-Storage

For water-wet porous media, the literature revealed a poor displacement efficiency for CO2 relative to N-2. The overall average residual water saturation displaced by CO2 is similar to 50.0% compared to similar to 20.0% displaced by N-2. Furthermore, based on the "Land" trapping model (Land, 1968), the non-wetting phase trapped during a subsequent imbibition displacement would also be reduced due to the low end-point saturation of the non-wetting phase achieved during the drainage flood. In this study, we hypothesize that for a drainage flood with a very low viscosity ratio (mu(displacing)/mu(displaced) <<1) and low flow rate (c(a) < 10(-6)) (i.e., conditions that are typical for the displacement of water by CO2, N-2 in a strongly water-wet porous media) the end-point residual water saturation is predominantly controlled by the interfacial tension of the fluid-gas system. To test our hypothesis, we have performed six pore-scale displacement experiments on a micromodel using both CO2 and N-2 to understand the influence of different fingering mechanisms (i.e., capillary vs. viscous) on flooding performance. It is observed that, for capillary-dominated floods, IFT values control the displacement efficiency. Therefore, we could conclude for capillary experiments that the poor displacement of the non-wetting (i.e., CO2) is due to a snap-off model which is closely related to the IFT value.