Page 55 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Low-Salinity Water Flooding: from Novel to Mature Technology 37

Zeinijahromi et al., 2011, 2013). However, fines migration and its size-
exclusion effects can also result in severe damage to reservoir permeability,
which leads to declines of well injectivity in the case of injection wells, and
productivity in case of production wells. During low-salinity waterflooding,
the majority of injection pressure loss occurs in the vicinity of the
wellbores. This is attributed to the high fluid flow velocities in these zones.
Therefore, understanding how to control or avoid fines migration in
reservoirs is an important issue for LSWF. On the one hand, it is desirable
to control fines migration to take advantages of its positive effects far
from the wellbore. On the other, it is important to minimize its negative
formation damage impacts near the wellbores. Here, we develop a mathe-
matical framework for designing a nanofluid-slug, preflush to enhance
well injectivity, while maintaining the mobility control assisted by fines
migration that contributes to improving LSWF performance (both EOR
and well injectivity).
During LSWF, the injected low-salinity fluid gradually sweeps out of
the reservoir the in-situ fluids with higher salinity. In the low-salinity
environment where smaller amounts of ions exist, according to the theory
of Debye and Hu ¨ckel (1923), the Debye-length (Double layer thickness
in of the 1910 Gouy-Chapman theory, Greathouse et al., 1994) would
increase. Therefore, the effects of fluid salinity can be reflected by changes
21
to the inverse Debye-length, κ,m (Elimelech et al. 1995), as shown in
Eq. (2.6):

s ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

ð
X
11
C mi;i S wc 1 C mi;j S w 2 S wc Þ
κ 5 0:73 3 10 z i 2 (2.6)

S w
th
where, C mi is the molar i ion concentration in water phase (injected and
3
th
initial conditions), moles/m ; Z i is a valence of i ion. This relationship
indicates that as the saturation of injected low-salinity water increases, the
inverse Debye-length would decrease; thereby, the repulsive energy
among the particles increases, and the bonding force among particles
attenuates. The double electric layer repulsive energy V DLR is described
by the DLVO (Derjagin Landau Verwey Overbeek) theory, as as
expressed by Eq. (2.7):
128πr FP n N k B T
V DLR 5 ς FP ς GS e 2κh (2.7)
κ 2