What Is A Separator In The Oilfield: Function, Types and Process Role What is a separator in the oilfield? An oilfield separator is a pressure vessel installed near the wellhead or at a gathering station that splits the raw well fluid, a mixture of crude oil, natural gas and produced water, into its separate phases by gravity settling, so each can be measured, treated and routed correctly. The two main classes are the two-phase separator, which divides gas from liquid, and