Page 92 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

74 Thomas Russell et al.

Figure 3.5 Increase of skin factor at the production well due to high-pressure
gradient, after switching the well on, and due to the arrival of “foreign” water.

Fig. 3.5 (Bedrikovetsky et al., 2011b). Switching wells on yields the crea-
tion of large pressure gradients in the vicinity of the wellbore, which
decrease with time and stabilize during the pressure wave propagation
into the formation. Equation (3.3) shows that the mobilized particles are
strained preferentially where the flow velocity is high, i.e., near to the
wellbore causing maximum damage. It corresponds to steep growth of
the skin factor. Pressure gradient stabilization leads to a stabilized skin
factor. The skin remains constant until the appearance of water in the
produced fluid. This could be either injected or aquifer water. The
particle detachment due to difference in compositions of formation and
breakthrough waters causes growing skin simultaneously with increasing
water-cut (Fig. 3.5). Skin growth during this second stage is substantially
higher when the injected (foreign) water has a smaller salinity than the
formation water.
The rate Eq. (3.3) with mass balance of attached, suspended, and
strained particles, and modified Darcy’s law accounting for permeability
damage by strained fines form a closed system of equations. Recently, the
analytical and numerical solutions of this system of equations have been
applied to well productivity and injectivity damage for single-phase and
two-phase flows.
Single-phase steady-state inflow well performance with fines migration
after stabilization shows zones of complete fines detachment, partial
detachment, and nonmobilized fines. It allows determining the size of
fines mobilization zone (Bedrikovetsky et al., 2012). Steady-state inflow
with fines migration occurs also during the intermediate production state,
where the decrease of fines mobilization due to spreading of pressure