We compare quantitatively two experimental situations concerning injection of a miscible fluid into an initially jammed
granular medium saturated with the same fluid, confined in a Hele-Shaw cell. The two experiments are identical, apart from the interstitial and injected fluid, which is in one case air injected into a dry
granular packing, and in the other case
silicone oil injected into a dense
suspension. In spite of the strong differences regarding the nature of the two fluids, strikingly similar dynamical and geometrical features are identified as functions of the control parameters: cell thickness and applied fluid injection pressure. In both cases an initial hydrodynamically driven decompaction process controls the unjamming and prepares the final displacement process characterized by fingerlike patterns empty of grains. The pattern shapes are comparable. In addition, the mobilities of the coupled fluid-grain
flow, rescaled by the
interstitial fluid viscosity and grain diameter squared, are of the same range and behave comparably. The mobility proves to depend on the initial
solid fraction of the medium. Subtle differences are observed in geometrical aspects like
the finger width
with respect to the control parameters.
