Page 226 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

200 Bin Yuan and Rouzbeh G. Moghanloo

In view of the variation of released fines concentration depending on
formation fluid velocities at different reservoir locations, it is necessary to
optimize the radius of nanofluid pretreatment to maximize the efficiency
of the nanoparticles treatment. Yuan (2017a) and Yuan and Moghanloo
(2018c) presented the comparison between the case with 0.01 nanofluid
pretreatment radius (Fig, 4.11B) and the reference case without nanofluid
utilization (Fig. 4.11A).
In Fig. 4.12, the time-distance diagrams of three different cases are
presented, including waterflooding without fines migration effects, water-
flooding with fines migration effects, and waterflooding with nanofluids
to control fines migration in the near-wellbore region. The time-distance
diagram for the waterflooding case without fines migration is presented in
Fig. 4.12A. The profiles of water saturation in an asymmetric system at
different moments in time can be achieved by finding the intersection
points of different horizontal lines (t D 5 const.) with the characteristic lines.
In Fig. 4.12B, the end points of series of characteristic lines (propaga-
tion path of water saturation wave) reflect the front-saturation along with
the waterflooding front shock. The values of front-saturation keep chang-
ing at different locations, which is attributed to the dependency of fines
migration on the changing flowing velocities at different reservoir loca-
tions in a radial flow system. The line connecting those points represents
the trajectory of the classical Buckley-Leverett waterflooding front. The
dashed line (gray) in Fig. 4.12B indicates the trajectory of the erosion
front (upstream, no fines attachment occurs; and downstream, fines
attachment occurs). The trajectory of the erosion front becomes a vertical
line, which indicates the erosion front is stationary at location of 0.1. In
other words, the propagation of the erosion front does not affect the
movement of water saturation waves.
Fig. 4.12C demonstrates the trajectories of the water-saturation waves,
and the movements of both erosion front and saturation-shock, for the
case with nanofluid treatment to control fines migration. In contrast to
Fig. 4.12B, the trajectory of the erosion front passes through the set of
saturation waves. In other words, the erosion front is not always ahead of
the water saturation waves, which can affect the propagation of water-
saturation waves.
Fig. 4.13 summarizes the evolution of the water saturation profiles in
the radial flow system at different times for the above three different cases.
First, the effects of fines migration (fines attachment, fines straining, and
fines suspension) can slow down the movement of injected water. The