What Is an Oilfield Three Phase Separator: Design, Weir and Interface Control Answering the core question: What is an oilfield three phase separator? An oilfield three phase separator is a horizontal pressure vessel that separates a wellstream into gas, crude oil and produced water in a single shell, using gravity for all three phases and internals to manage the oil-water interface. Gas is separated by the Souders-Brown velocity limit with a K factor of 0.10-0.25 m/s, while