Page 60 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

42 David A. Wood and Bin Yuan

However, in the presence of fines migration effects, the characteristic lines
are no longer straight; therefore, the water-saturation values, also, would
not remain constant along those the curved characteristic lines. As the
water-saturation wave with a specific injected water saturation at the inlet
(injection well) moves toward the outlet (production well), the corre-
sponding water saturation progressively decreases and the velocity at
which that saturation wave moves (i.e., the slopes of characteristic lines)
increase, as indicated in Fig. 2.10.
By drawing vertical lines with constant time (for example, t D 5 0.2)
passing through the characteristic lines with varying water saturation, the
water saturation distribution in a radial flow system can be derived. The
comparisons of the water saturation profiles at specific times between
conventional waterflooding and low-salinity waterflooding are illustrated
in Fig. 2.11. A key effect of fines migration is to decrease the effective
water-phase permeability, which can significantly slow down the move-
ment of the injected water. This confirms the effectiveness of induced
fines migration during low-salinity waterflooding to improve the
mobility-control performance by slowing down the flow of injected water
through the reservoir.
Nanoparticles can effectively enhance the attractive forces between
fine particles and grain surfaces by changing the surface zeta potentials of
fine particles, and significantly mitigating formation damage caused by

0.9
LSW flooding with fines migration
0.8
Water flooding without fines migration
0.7
Water saturation, S w 0.5
0.6

0.4
0.3
0.2
0.1
0
0 0.2 0.4 0.6 0.8 1
Dimensionless distance, x D
Figure 2.11 Water saturation profiles of conventional waterflooding cases and low-
salinity waterflooding cases with fines migration effects at the same moment.