Page 212 - Well Control for Completions and Interventions

Completion, Workover, and Intervention Fluids 205

5.6.4 Brine additives
A number of different chemicals are routinely added to completion and
intervention brine. Adding these chemicals changes brine chemistry and
can increase the potential for a brine to damage the formation. The most
commonly used brine additives are listed and described in Table 5.7.

Table 5.7 Brine additives
Additive Function
Clay inhibitors Used mainly with low density (low salinity) brines,
these organic compounds are used to inhibit the
swelling of pore lining clays. They are mixed
directly into a brine at the surface.
Caustic soda (sodium Low pH brines are corrosive. Adding caustic soda or
hydroxide) and magnesium oxide increases the pH and reduces
magnesium oxide corrosion. Increasing pH can lead to fines
mobilization.
Corrosion inhibitors These are used to limit tubular corrosion. They are
often oil wetting, and therefore damaging to the
formation. Highly toxic in concentrated form,
there are HSE risks associated with their use.
The use of thiocyanate corrosion inhibitor had been
discontinued by some operating companies, as there is
evidence to suggest that it breaks down at high
temperature with corrosive H 2 S as a by-product. a
Surfactants These are used to prevent secondary emulsions.
Surfactants also improve the dispersion of other
additives used in completion fluids.
Defoamer As the name suggests, defoamer is used to reduce
foaming when mixing surfactants and some types of
corrosion inhibitors.
Friction reducers Polymers (such as polyacrylamide) are used to reduce
the coefficient of friction. This reduces tubing-to-
casing friction when running coiled tubing and
completion tubing, and also reduces frictional
pressure drop when circulating fluids. They are
widely used when fracturing unconventional (shale)
formations.
Oxygen scavenger Used to reduce/eliminate free oxygen from the fluid
system.
Biocide Used to control sulfate reducing bacteria and acid
producing bacteria. They are not normally required
in brine with a high salt content.
a
Mingjie K, Qi Q. Thermal decomposition of thiocyanate corrosion inhibitors: a potential problem
for successful well completions. SPE paper 98302, 2006.