Disorder-Induced Capillary Bursts Control Intermittency in Slow Imbibition

A multiscale analysis of the spatially averaged velocity of an imbibition front V_(t) measured at scale reveals that the slow front dynamics is intermittent: the distributions of ΔV_(τ)=V_(t+τ)-V_(t) evolve continuously through time scales τ, from heavy-tailed to Gaussian---reached at a time lag τc set by the extent of the medium heterogeneities. Intermittency results from capillary bursts triggered from the smallest scale of the disorder up to the scale c at which viscous dissipation becomes dominant. The effective number of degrees of freedom of the front /c controls its intensity.