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 N₂. The overall average residual water saturation displaced by CO₂ is ~50.0% compared to ~20.0% displaced by N₂. 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 (μ_displacing/μ_displaced <<1) and low flow rate (c_a < 10^–6) (i.e., conditions that are typical for the displacement of water by CO₂, N₂ 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 N₂ 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.