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Paniculate Processes in Porous Media 155
decreases. Gruesbeck and Collins (1982) also observed a similar phenom-
ena in systems of homogeneous grain sizes subjected to a constant rate
injection of a suspension of particles.
Millan-Arcia and Civan (1992) have reported frequent fluctuations in
the effluent fluid concentrations and pH during injection of brine into
sandstone (see Figure 8-8).
Colloidal Release and Mobilization
Colloidal mobilization is a result of the physico-chemical reactions
that involve electro-kinetic forces, zeta potential, and ionic strength
(Wojtanowicz et al., 1987). Let e p denote the volume fraction of porous
media occupied by the particles available for mobilization over the pore
surface. The rate of colloidal expulsion or mobilization of particles at the
pore surface is proportional to the excess critical salt concentration (c cr - c),
8,5
Q Core 24
• Core30A
7,5-
a a Q a
a a
6,5
100 200 300 400
Pore Volumes Injected, pv's
Figure 8-8. Effect of frequent pore throat plugging and unplugging by particles
on the effluent solution pH (Arcia and Civan, ©1992; reprinted by permission
of the Canadian Institute of Mining, Metallurgy and Petroleum).
