Page 210 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

184 Bin Yuan and Rouzbeh G. Moghanloo

medium to capture unsettled fines: (1) coinjection of nanoparticles with
fines suspension into porous medium; and (2) precoating medium with
nanoparticles prior to fines invasion.

4.4.1 Approach I: Coinjection of nanoparticles
and fines into porous media
Usually, the surface potential of fines is less than that of rock grains,
which results in the stronger attractive force between nanoparticles and
fines than that between nanoparticles and rock grains (Yuan et al., 2016
and 2018b). Hence, during the co-injection of a mixture of nanoparticles
and fines, nanoparticles should be assumed to be preferentially adsorbed
onto the surfaces of mobile fines rather than the surfaces of rock grains.
As a result, the nanoparticles adsorption onto fines would alter the surface
potential of fines, which consequently enhance the attractive force
between fines and rock grains. This is why the co-injection of nanoparti-
cles could help increase the maximum retention concentration of fines
onto rock grains.
As shown in Fig. 4.3a, the attachment of fine particles onto rock
grains has already reached the maximum retention concentration of fines
initially (Eq. 4.6a), which is determined by the surface charge of fine par-
ticles and rock grains. However, still excessive unattached fines are left in
flowing suspension through porous medium. As nanoparticles arrive, the
already attached fine particles onto rock grains would not be the immedi-
ate targets to capture nanoparticles; instead, the remaining unattached
fines in the carrier suspension are more prone to first host the arriving
nanoparticles. Continuously, the more nanoparticle adsorption, the larger
the decrease of the surface potential of fines; thus, the attractive electro-
static forces between unattached fines and rock grains could be further
enlarged. As a result, more attachment of initially unattached fine particles
onto the pore surface instantaneously occurs following the adsorption of
nanoparticles onto their surfaces. The n-nanoparticles-fine complex
would be attached onto the rock grain surfaces continuously until the
attachment of fine particles with nanoparticles adsorption onto rock
grains reaches a new maximum limit (Eq. 4.6b), which is controlled by
the maximum amounts of nanoparticles adsorbed onto suspended fines.
The stepwise reaction process of nanoparticles adsorption and subsequent
n-nanoparticles-fine complex attachment would continuously repeat,
and thus more unattached fines can be retained by rock grains with the
increase of nanoparticles adsorption onto their surfaces (Yuan et al., 2018b).