Oil production plant  An oil production plant is a facility which processes production fluids from oil wells in order to separate out key components and prepare them for export. This is distinct from an oil depot, which does not have processing facilities. Typical oil well production fluids are a mixture of oil, gas and produced water. Many permanent offshore installations have full oil production facilities. Smaller platforms and subsea wells export production fluids to the nearest production facility, which may be on a nearby offshore processing installation or an onshore terminal. The produced oil may sometimes be "stabilised" (a form of distillation) which reduces vapour pressure and sweetens "sour" crude oil by removing hydrogen sulphide, thereby making the crude oil suitable for storage and transport. The production plant can be considered to begin after the production wing valve on the oil well Christmas tree. The reservoir fluids from each well are piped through a flowline to a choke valve, which regulates the rate of flow and reduces the pressure of the fluids. The flowlines from each well are gathered together at an inlet manifold and routed into a (first stage) separator, which separates the three fluid phases. Produced water, the densest phase, settles out at the bottom of the separator, oil floats on the top of the produced water phase, and gas occupies the upper part of the separator. Oil from the first stage separator may be cooled or heated in a heat exchanger to aid further separation. Oil is then routed either to a second stage separator, operating at a lower pressure than the first stage to further separate oil/gas/water, or to a coalescer to further remove water. Several stages of separation, operating at successively lower pressures, aim to reduce the amount of dissolved gas and hence reduces the flash point of the oil to meet the export oil specification. For higher oil flowrates parallel trains of separators may be necessary to handle the flow and to provide a turn-down capability. From the final stage of separation, or from the coaleser, oil may be cooled to meet export specifications and is metered to accurately measure the flowrate and then pumped via a pipeline to the onshore terminal. Some installations such as concrete gravity-base structures and FPSOs have integral oil storage tanks which are continuously filled with oil and periodically discharged into oil tankers. Produced water from the separator(s) or coalescer is routed to a produced water degasser operating at near atmospheric pressure to remove dissolved gas from the water. Produced water is then routed to a hydrocyclone to remove entrained oil and solids and then either re-injected into the reservoir or dumped overboard.