Oil and gas production handbook An introduction to oil and gas production

Polyelectrolyte 
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 (MEG) 
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.