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An oil production plant (sometimes called an oil terminal) is a facility which performs processing of 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 production fluids are a mixture of oil, gas and produced water. Many permanent offshore platforms have full oil production facilities on board. Smaller platforms and subsea wells must export raw production fluid to the nearest production facility, which may be on a nearby offshore processing platform or an onshore terminal.
Sometimes the produced oil may be stabilised (a form of partial distillation) which reduces vapour pressure and sweetens "sour" crude oil by removal of hydrogen sulphide, thereby making the crude oil safer for storage and transport.

Process

The production plant can be considered to begin after the production wing valve on the oil well Xmas tree. The production fluids from each well are piped through a flowline to a choke valve, which regulates the rate of flow from each well and reduces the pressure of the well fluids. The flowlines 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 is routed either to a second stage separator, operating at a lower pressure than the first stage separator to further separate oil/gas/water, or to a coalescer to further remove water. Several stages of separation at successively lower pressures aims to reduce the flash point of the oil to meet any export oil specification. From the final stage of separation, or from the coaleser, oil is metered to accurately measure the flowrate and then pumped to the onshore terminal.  

Produced water from the separator(s) can be routed to a hydrocyclone to remove entrained oil and solids and then either re-injected into the reservoir or dumped overboard. In the early days of the industry dissolved gas flotation units were used to clean produced water prior to overboard disposal. Hydrocyclones are more compact.

The associated gas from the top of the separator(s) is also known as "wet gas" as it is saturated with water and liquid alkanes. The gas is typically routed through scrubbers, compressors and coolers to raise the pressure of the gas and to remove the liquids. Gas is usually dried by counter-current contact with triethylene glycol in a dehydration tower. This "dry gas" may be exported, used for gas lift, flared, used as fuel for the installation's power generators, or after further compression re-injected into the reservoir. Dry gas may be further treated to meet export gas specifications. Excess carbon dioxide can be removed by treatment with an amine solvent. Hydrogen sulphide can also be removed using amine or by passing the gas through beds of zinc oxide. The export hydrocarbon dew-point specification may be met by chilling the gas to remove the higher alkanes. This may be done by refrigeration, passing the gas through a Joule-Thomson valve, or through a turbo-expander. Export gas is metered to accurately measure the flowrate before being sent to the onshore terminal. Condensed liquids from the gas treatment plant may be stabilised in a stabiliser column to produce a gas product which can be co-mingled with the gas streams and natural gas liquids (NGL) which can be co-mingled with the oil export stream.

Onshore terminals generally have fired heaters followed by separators and coalescers to stabilise the crude and remove any produced water not separated offshore. Onshore separators tend to operate at a lower pressure than the offshore separators and so more gas is evolved. The associated gas is generally compressed, dew-pointed and exported via a dedicated pipeline. If gas export is uneconomical then it may be flared. Onshore terminals frequently have large crude oil storage tanks to allow offshore production to continue if the export route becomes unavailable. Export to the oil refinery is either by pipeline or tanker.

See also

• Petroleum


• Oil industry


• Upstream (oil industry)


• Chemical plant


• Oil refinery

External links

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• Production Facility