DETERMINATION OF COLLOID DEPOSITION AT GRAIN-GRAIN CONTACTS USING X-RAY MICROTOMOGRAPHY

The deposition of near-neutrally buoyant x-ray visible microspheres was examined in porous media of different grain sizes and angularities under both favorable and unfavorable deposition conditions. Colloid-grain diameter ratios were varied to span thresholds previously identified for physical straining. The environment of microsphere deposition was determined in-situ using x-ray microtomography. The relative prevalence of deposition at grain-grain contacts was determined for various flow velocities. Medial axis analysis yielded characterization of the pore structures, and provided the quantitative basis for comparison of the prevalence of deposition at grain-grain contacts among the different porous media. The mechanisms of colloid deposition in grain-grian contacts (e.g. interception, rolling subsequent to interception) were examined via subsidiary experiments. The relationship of deposition at grain-grain contacts relative to physical straining was examined. The impact of colloid deposition at grain-grain contacts on colloid transport was discussed.