The primary activity in surface processing facilities
is separating the produced fluids into streams of oil,
gas and water for sale and disposal. This separation is
accomplished largely by gravity segregation, drawing
the lighter gas off the top of the separator vessels, the
heavier water off the bottom, with only the oil remaining.
The first pressure vessel the fluid will enter at the central
facility is the gas separator, typically referred to as "the
separator." It removes the free gas from the liquid. Most
separators are two-phase, separating the gas phase from
the liquid phase, which includes both water and oil.
Vertical separators are used for low volume operations,
while horizontal separators are typically used in high
volume, high GOR "Gas/Oil Ratio" applications. Three
phase separators that divide the production into three
streams of oil, gas and water are usually used with high
gravity oils that readily separate from the water.