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Transport of polydisperse colloid suspensions in a single fracture

Chrysikopoulos Constantinos, Scott C. James

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Summary

The transport of variably sized colloids (polydisperse) in a fracture withuniform aperture is investigated by a particle-tracking model that treats colloids asdiscrete particles with unique transport properties while accounting for either matrixdiffusion or irreversible colloid deposition. For the special case of a monodisperse colloidsuspension the particle-tracking model is in perfect agreement with predictions based onan existing analytical solution. It is shown that lognormal colloid size distributions exhibitgreater spreading than monodisperse suspensions. Increasing the fracture porosity of thesolid matrix leads to higher matrix diffusion, which in turn delays particle breakthroughfor both the monodisperse and variably sized colloid suspensions. The smallest particles ofa distribution are more greatly affected by matrix diffusion whereas the largest particlesare transported faster and further along a fracture. Both perfect sink and kinetic colloiddeposition onto fracture surfaces are examined. Kinetic deposition accounts for colloidsurface exclusion by either a linear or nonlinear blocking function. For both cases thesmallest colloid particles tend to preferentially deposit onto the fracture wall. Both matrixdiffusion and surface deposition tend to discretize colloid distributions according toparticle size so that larger particles are least retarded and smaller particles are moreslowly transported. Furthermore, it is shown that the rate of colloid deposition is inverselyproportional to the fracture aperture.

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