Page 174 - Reservoir Formation Damage

156 Reservoir Formation Damage

and the amount of the unblocked particles at the pore surface available for
mobilization, £r\ e.

(8-26)

subject to

(8-27)

a is the volumetric expansion coefficient for swelling clays as described
in Chapter 2; ot = 0 for nonswelling particles; c cr is the critical salt concen-
tration; and r\ e is the fraction of the unblocked particles approximated by
(see Figure 8-3) (Civan et al., 1989; Ohen and Civan, 1993; Civan, 1996):

= exp (8-28)

A, is an empirical constant; 2-> p represents the total volume of various
p
types of particles retained within the pore space; k r is a particle release
rate constant given by (Khilar and Fogler, 1987, 1983; Kia et al., 1987):

k, ^ 0 when c < (8-29)

and

k, = 0 otherwise (8-30)

Hydraulic Erosion and Mobilization
The rate of hydraulic mobilization of the particles at the pore surface
is proportional to the excess pore wall shear stress, (T w -T cr ), and the
amount of the unblocked particles available for mobilization at the pore
surface (Gruesbeck and Collins, 1982; Khilar and Fogler, 1987; Cernansky
and Siroky, 1985; Civan, 1992, 1996).

(8-31)
dt