Oil and gas production handbook An introduction to oil ... - ABB Group

Polyelectrolyte
Methanol (MEG)
TEG
Hypochlorite
Biocides
mist and liquid drops. An antifoam agent is introduced
upstream of the separator to prevent or break down
foam formation by reducing liquid surface tension.
Polyelectrolyte is added before the hydrocyclones and
causes oil droplets to merge. This works by reducing
surface tension and water polarity. This is also called
flocculation, and polyelectrolyte flocculants allow
emissions to reach 40 ppm or less.
Methanol or monoethylene glycol (MEG) is injected in
flowlines to prevent hydrate formation and prevent
corrosion. Hydrates are crystalline compounds that
form in water crystalline structures as a function of
composition, temperature and pressure. Hydrates
appear and freeze to hydrate ice that may damage
equipment and pipelines.
For normal risers, hydrates form only when production
stops and the temperature starts to drop. Hydrate
formation can be prevented by depressurization which
adds to startup time, or by methanol injection.
On longer flowlines in cold seawater or Arctic
climates, hydrates may form under normal operating
conditions and require continuous methanol injection.
In this case, the methanol can be separated and
recycled.
Hydrate prediction model software can be used to
determine when there is a risk of hydrate formation
and to reduce methanol injection or delay
depressurization.
Triethyleneglycol (TEG) is used to dry gas (see the
chapter on scrubbers and reboilers).
Hypochlorite is added to seawater to prevent growth
of algae and bacteria, e.g., in seawater heat
exchangers. Hypochlorite is produced by electrolysis
of seawater to chlorine. In one variant, copper
electrodes are used, which adds copper salts to the
solution that improves effectiveness.
Biocides are also preventive chemicals that are added
to prevent microbiological activity in oil production
systems, such as bacteria, fungus or algae growth.
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