Page 132 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

112 Thomas Russell et al.

Two additional curves are shown to demonstrate the effect of produc-
tion rate. Larger rates create higher fluid velocities in the reservoir which
consequently result in more fines detachment and formation damage.

3.5 FINES DETACHMENT AND MIGRATION
AT LOW SALINITY

Weakening of the electrostatic force between particle grains during
low-salinity waterflooding will lead to particle mobilization, as discussed
in Section 3.2. Formation damage during low-salinity waterflooding due
to fines mobilization, migration, and straining in thin pores has been
widely presented in the literature (Civan, 2014; Sarkar and Sharma,
1990). Significant pressure-drop increase and fines appearance in the core
outlet have been observed during numerous corefloods with injection of
low-salinity or fresh water (Morrow and Buckley, 2011).
This section presents a mathematical model for fines migration during
low-salinity waterflooding. Different from the model for particle detachment
due to velocity alteration discussed in Section 3.3, in the case for particle
detachment due to salinity alteration particles only detach upon the arrival
of the injected low-salinity water. Therefore, it is not possible to assume that
particles detach as soon as the salinity of the injected water changes and an
equation that describes the transport of salt must be included.

3.5.1 1D analytical solution with instant fines detachment

During low-salinity waterflooding, the colloidal-suspension flux is assumed
to be incompressible, so the carrier water flux U(t) is constant (Barenblatt
et al., 1989; Lake, 2010). All particle concentrations are small enough not to
affect the volumetric water balance. Porosity is considered to be constant.
Particles drift with velocity αU that is significantly lower than the carrier
water velocity U,i.e., α ,, 1,as stated in Section 3.3 (Oliveira et al., 2014;
Yuan and Shapiro, 2011). Particle and salt diffusion are ignored.
To take into account the water salinity alteration, it is necessary to
introduce the mass balance equation for salt transport:
@γ @γ
φ 1 U 5 0; (3.92)
@t @x
where γ is the salinity.