Page 262 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Formation Damage by Inorganic Deposition 233

10 1
10 0 X = 0.9
10 –1
–2
Permeability ratio 10 –3 X = 0.3
10
–4
10
–5
10
10 –6 X = 0.1

10 –7
10 –8
10 –9
0.0 0.2 0.4 0.6 0.8 1.0
Porosity, fraction
Figure 5.9 Impact of pore radius reduction on permeability and porosity as the
result of scale deposition using the modified Carman-Kozeny model. Here, X is the
radius ratio of reduced radius to the original radius.

Fig. 5.9 shows the severity of permeability reduction as a result of
scale deposition for variable formations. The figure shows that the perme-
ability ratio decreases significantly when the thickness of precipitation
increases.

5.3.4 Scale inhibitors
Scale inhibitors are most often used as a prevention technique to reduce
the scaling risks in near wellbore location and wellbore (Shaughnessy and
Kline, 1983). From the process of scaling formation, scale inhibitors can
work in one or more of three ways. Fig. 5.10 shows a summary diagram
for main mechanisms of scale inhibitors.
Some scale inhibitors can interfere with the nucleation process by dif-
fusing in the bulk liquid to reach the ion clusters either in the liquid or
on a solid substrate. These inhibitor ions should be of a sufficiently large
size to disrupt the scaling ion clustering and prevent further growth of
existing clusters to the critical size where crystallites would form. A good
nucleation inhibitor ion needs to be of a critical size but still be able to
diffuse in the water at an acceptable rate.
Some inhibitors do not prevent the nucleation to cluster, but retard
the crystal growth by diffusing over the crystal surface and active sites