VISUALIZATION OF COLLOID REMOVAL AT THE PORE SCALE IN SATURATED POROUS MEDIA

Colloid transport is studied at the pore-scale in order to gain insight into the processes governing particle removal. Monodisperse suspensions of colloids and homogeneous transparent PDMS micromodels with pore throats in the order of 6-10 &mum are employed. Experiments are carried out for different particle sizes, surface roughness of the pore grains and flow rate conditions. Straining and attachment are observed and measured by tracking the trajectory and fate of individual colloids using optical microscopy. Results of theses experiments indicate that the mechanisms of removal and the spatial distribution of colloid retention differ greatly as a function of the T/C ratio (pore throat/colloid diameter). Straining is found to be important for small T/C ratios. Removal increases with increasing surface roughness and decreasing the flow rate. For a given flow velocity there is a limited number of sites available for attachment. As favorable sites are been filled a constant decrease in retention is observed. The role of hydrodynamic interactions on colloid deposition will be discussed.