Page 51 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Low-Salinity Water Flooding: from Novel to Mature Technology 33

on them. By weakening the electrostatic forces, LSWF can, in certain
conditions, disturb that equilibrium leading to fines particles being
dislodged from the pore linings and dragged along with flowing forma-
tion water into pore throats (Fig. 2.6), some of which will become
blocked by those dislodged particles (Khilar et al., 1983).
Bedrikovetsky et al. (2012) proposed a maximum retention function
that could be used to model fines migration in porous media. This involves
the calculation of the torque balance of forces to calculate the maximum
concentration of particles that can remain attached to the pore walls. The
mechanical equilibrium of a particle can be expressed as Eq. (2.1).

(2.1)
F d ðUÞl d 1 F l ðUÞl n 5 ðF e ðγÞ 1 F g Þl n
where: γ is salt concentration, U is the Darcy velocity, and l d and l n repre-
sent levers for drag and normal forces, respectively. If the detaching forces
(left-hand side Eq. (2.1): torque /drag F d and lift F l ) are greater than the
attaching forces (right-hand side Eq. (2.1): gravity F g and electrostatic F e )
the hydrodynamics of the flowing formation water is likely to dislodge
the particle (Fig. 2.7). LSWF can cause the electrostatic forces to reduce
and mobilize the particle.

Figure 2.6 Schematic of fines distribution and mobilization within porous rock.
Modified after Khilar et al. (1983).