Page 221 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Using Nanofluids to Control Fines Migration in Porous Systems 195

In Fig. 4.9A, the coordinates of the stream-function and distance, the
corresponding characteristic lines of nanoparticles, and fines concentra-
tions that vary from the injection condition to the initial condition, are
obtained. This is followed by an inverse transformation of the stream-
function back to time as the independent variable using Eq. (4.16). Along
the characteristic lines in Fig. 4.8A, the constant values of component
concentrations (nanoparticles, fines, and water) lead to the inversed trans-
formation as straight-line images of t D in Fig. 4.8B.
ð x D ;ϕÞ 1 S w x D ; ϕÞ
ð
ð
t D 5 dϕ 1 dx D (4.16)
f w x D ; ϕð Þ f w x D ; ϕð Þ
ð 0;0Þ
Displayed in different coordinates, Fig. 4.9 indicates that the charac-
teristic velocities (slope of characteristic lines) are different. Using the
distance-time diagram of Fig. 4.8B, the intersection points of horizontal
lines (t D 5 const.) with the characteristic lines determine the profile of
component concentrations through a 1-D porous medium.
Accompanying the discontinuities of particles-concentration waves,
c-shock1, and c-shock2, are the discontinuities of the water saturation
wave, where water saturation decreases from 0.76 upstream to 0.696
downstream of c-shock1, and increases from 0.66 upstream to 0.693
downstream of c-shock2. In the initial-condition region with constant
nanoparticles and fines concentration, analogos to the classical Buckley-
Leverett problem, the Sw-shock appears because of the discontinuity of
fraction flow curve, where water saturation decreases directly from 0.66
to the connate-water saturation 0.20. Nanoparticles coinjection can help
enhance the attachment of fine particles onto pore surfaces (preferentially
in the higher-Sw regions), which results in more damage to the water-
phase relative permeability. Hence, as a positive consequence, nanoparti-
cles utilization leads to the formulation of an “oil-bank” in the region
between c-shock1 and c-shock2, as shown in Fig. 4.10.

4.5.2 Nanofluid preflush to control fines migration in a radial
flow system saturated with two immiscible fluids
It is also recommended to precoat porous medium using nanoparticles
prior to waterflooding to prevent the induced fines migration by injected
fluids. In this section, fines migration affecting two-phase (oil and water)
radial flow is discussed incorporating multiple fines capture phenomena,
i.e., fines attachment and straining. The performance of nanofluid