Understanding and controlling particle transport in porous media is of widespread interest across diverse practical applications. Here, we report geometry-mediated accumulation effect on particle transport under dilute conditions driven by the interplay between particle lagging and viscosity effect, offering an alternative perspective for preferential flow control in porous media. Pore-to-throat velocity variations can trigger strong local accumulation of microgel particles in the absence of clogging effects, which is anomalous given the low Stokes number. Based on volume-averaged equations for two-phase flow, we theoretically elucidate the competition between the drag force representing particle-fluid interactions and an additional resistance force representing interparticle interactions, which governs particle accumulation and becomes significant only with concentration-sensitive viscosity. Differing from shear-induced migration driven by multibody hydrodynamic or collision interactions at higher concentrations, such accumulation occurs only in the presence of geometry variations, highlighting its promising impact on suspension flow in porous media. A new dimensionless number is proposed and validated by numerical simulations in typical pore-throat geometries to generally describe the triggering criterion and accumulation intensity. Investigations in heterogeneous porous media reveal varying accumulation patterns under various injection conditions, which are predictable applying theoretical descriptions. Unexpected preferential flow control performances arise from lateral flow reallocation, controlled by the formation and distribution of localized intense accumulation zones. Our findings provide insights into particle transport mechanisms and flow control strategies in microchannels and porous media.

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• Flows in porous media