Pore-scale investigation of immiscible fluid displacement process in randomly distributed bead-based porous micromodels using Micro-PIV

This study reports pore-scale immiscible displacement processes in a bead-based porous micromodel using fluorescence microscopy and micro-particle image velocimetry (mu-PIV) technique. The porous micromodels with heterogeneous and homogeneous geometry are fabricated to investigate the effect of displacing phase viscosity and flow rate on the pore-scale displacement mechanism. The phenomena of shear-induced circulations and viscous instability are observed during the displacement of the trapped non-wetting phase through the porous domain. Breakage and coalescence of the droplets of the non-wetting phase were also observed during the displacement process. The velocity vector maps show that there is frequent flow reversal of ganglia, leading to an unsteady flow behaviour during the displacement process. The effect of flow rate and viscosity on the trapped non-wetting phase is investigated, and the results obtained indicate that an increase in the flow rate reduces the trapped non-wetting fluid saturation in the porous medium by disintegrating large ganglia into small droplets. Increasing either the flow rate or viscosity increases the shear stress at the interface of the trapped ganglion and displacing phase, leading to shear-induced circulations, and the strength of the vortex is found to increase. These circulations inhibit further displacement of the trapped fluids. At higher flow rate with more viscous displacing phase, the trapped non-wetting phase ganglion disintegrate into smaller droplets. It is observed that a heterogeneous micromodel causes significant trapping and lesser mobilization of the non-wetting phase compared to a homogeneous system. The porous medium with low porosity and a higher degree of heterogeneity results in more trapping and less recovery of the non-wetting phase.