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

sand cyclone, which removes most of the sand. The sand is further washed 
before it is discharged.  
 
The water then goes to a hydrocyclone, a centrifugal separator that 
removes oil drops. The hydrocyclone creates a standing vortex where oil 
collects in the middle and water is forced to the side. 
 
Finally the water is collected in the water de-gassing drum. Dispersed gas 
slowly rises and pulls remaining oil droplets to the surface by flotation. The 
surface oil film is drained, and the produced water can be discharged to sea. 
Recovered oil in the water treatment system is typically recycled to the third 
stage separator. 

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4.3  Gas treatment and compression 
The gas train consists of several stages, each taking gas from a suitable 
pressure level in the production separator's gas outlet, and from the previous 
stage. 
 
A typical stage is 
shown on the right. 
Incoming gas (on 
the right) is first 
cooled in a heat