Page 263 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

234 Xingru Wu

Supersaturated solution
Chelation
Nucleation
Nucleation inhibition
Crystal growth
Flocculation Crystal growth
dispersion modification
Adherence
Figure 5.10 Summary of scale inhibitor mechanisms in different stage of scale-
forming process.

through a strong affinity. This type of inhibitor has to be sufficiently small
to be diffused, but sufficiently large in order not to be absorbed into the
growing crystals. Different from the first kind inhibitor, this type of
inhibitor promotes the formation of small crystals to reduce the supersat-
uration of the solution and lower the risk of scaling in following parts of
flow conduit. If the inhibitor is absorbed into the crystal, it can be con-
sidered advantageous in that the resulting scale may be soft, friable, and
easily removed.
Some inhibitors can modify the crystal surface. The transport theory
and models of scale inhibitor can be found in the literature (Sorbie and
Gdanski, 2005, Kahrwad et al., 2009). Molecules that are neither nucle-
ation nor crystal growth modifiers are able to absorb strongly to crystal
surfaces and prevent attachment of crystals.
Selecting the right inhibitor is critical in scale management and timing
of inhibition is also important. Fig. 5.11 is an illustrative diagram for scale
index change with time and when scaling inhibitors should be deployed.
Even though the diagram is made for sulfate scales, other scales also quali-
tatively follow similar trends.

5.4 MANAGEMENT OF SCALING IN DEVELOPMENT
AND PRODUCTION

The management of scaling occurrence during the development
and production of an oil & gas field is done mainly to reduce the risk of
scaling formation in reservoir and production facilities, especially in the
near-wellbore formation and wellbore. It is possible to have a severe