Transition from viscous fingers to compact displacement during unstable drainage in porous media
Fredrik Kvalheim Eriksen, Marcel Moura, Mihailo Jankov, Antoine Turquet, Knut Jørgen Måløy
Abstract
The immiscible displacement of a viscous fluid by a less viscous one in a porous medium is known to be unstable and often results in dendritic fingering patterns, where the pressure gradient is screened internally and only advanced invading parts grow. We present experiments in porous media, systematically varying the imposed injection pressure ($P$) and viscosity ratio ($M$) of the invading to defending fluid. A crossover to more stable and compact invasion structures is found for higher $P$ and $M$. This compact invasion regime onset is observed even for $M<{10}^{\ensuremath{-}3}$. We show that the pressure gradient is not screened in this regime and invasion patterns exhibit rich internal flow dynamics.