Viscous fingering in polymeric fluids

The flow displacement process, through microchannel or porous media, suffers from a fingering phenomenon that manifests in the form of finger-like patterns around the interface region. Viscous fingering instability can be controlled by adding polymers to either displacing or displaced fluid which alters the fluid viscosity, the cause of viscous fingering. The shear-rate-dependent viscosity and elasticity of polymeric fluids influence the growth of fingers mainly due to non-uniform viscosity distribution. To investigate the role of rheological properties on instability, the miscible flow displacement is studied experimentally using the Hele-Shaw cell. The aqueous solutions of polyethylene oxide (PEO) of varying concentrations and molecular weights are used as one of the fluids. The visualization of fingers shows that displacement of PEO solutions at high concentration or high molecular weight leads to more complex and fractal-like patterns with tip-splitting and side-branching mechanisms. For similar viscosity contrast between two fluids, the finger formation is found to be more intensified when displaced fluid is polymeric in nature as compared to displacing fluid being polymeric fluid. The shear-thinning behavior strengthens shielding behavior whereas fluid elasticity leads to tip-spitting, irrespective of the flow arrangement.