(469f) Controlling Immiscible Fluid Displacement Using Pore Size Gradients in Disordered Media

Capillary fingering is a fluid instability that occurs when a non-wetting fluid displaces a wetting fluid from a porous medium. This instability can affect groundwater contamination, oil recovery, and agricultural irrigation. Using microfluidic experiments and pore-network models, we show that capillary fingering is strongly influenced by a pore size gradient. We find that the non-wetting fluid displacement pathway depends sensitively on the direction and the magnitude of the gradient, enabling the flow to either be completely stabilized or destabilized. By analyzing capillary forces at the pore scale, we develop a geometric criterion that predicts when capillary fingering is completely suppressed. Our results thus help elucidate how diverse flow pathways can be controlled in disordered media.