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Emulsion (water-in-oil)

A water-in-oil emulsion is a dispersion of small water droplets in crude oil, held apart by natural surface-active films of asphaltenes, resins, waxes and fine solids. The droplets will not settle until those films are broken and the droplets merge.

Also written as: water-in-oil emulsion

Emulsion (water-in-oil) explained

Emulsions form where oil and water are sheared together: at chokes, pumps and control valves. Stability rises with smaller droplets, heavier and more viscous crude, lower temperature and more fine solids. Heat, demulsifier chemical, residence time and an electrostatic field are the four tools used to break them.

  • Electrostatic coalescers

    An electrostatic coalescer is a pressure vessel that uses a high-voltage electric field to merge small water droplets in crude oil into drops large enough to…

  • Electrostatic coalescer prewash

    An electrostatic coalescer prewash removes entrained caustic from kerosene after the caustic prewash of a kerosene sweetening unit. A high-voltage direct current (DC) field makes the…

  • Crude oil heaters

    A crude oil heater raises crude to the temperature at which water can be separated from it. In oilfield treatment this is usually an indirect fired…

  • Crude oil dehydrators

    A crude oil dehydrator is an electrostatic coalescer used to remove produced water from crude so that it meets its basic sediment and water (BS&W) specification.…

  • Crude oil desalters

    A crude oil desalter removes salt from crude by mixing in low-salinity wash water to dilute the brine, then removing the water in an electrostatic coalescer.…

  • Crude oil treatment

    A crude oil treatment system removes water, salt and sediment so that crude meets its sales or refinery specification. It works as a train: separation, heating,…

  • Troubleshooting and performance diagnostics

    Troubleshooting a desalter, dehydrator or hydrogen pressure swing adsorption (PSA) unit starts with the symptom, because each symptom has a short list of probable causes and…

Basic sediment and water (BS&W)
Basic sediment and water (BS&W) is the combined volume of water and solid sediment in a crude oil sample, reported as a volume percentage. It is the usual measure of how well crude has been dehydrated before sale or refining.
Demulsifier
A demulsifier is a surface-active chemical injected into crude oil at parts-per-million levels to displace the natural films that stabilise water droplets. With the films weakened, droplets can merge and settle. It works together with heat, time and electrostatic fields.
Rag layer
A rag layer is a band of emulsion and solids that collects at the oil-water interface in a separator or desalter. As it grows it reduces settling volume, confuses level instruments and may reach the electrodes or the water outlet.
Electrostatic coalescence
Electrostatic coalescence is the use of a high-voltage electric field to make small water droplets dispersed in oil collide and merge into larger droplets. Larger droplets settle much faster under gravity, so water separates from crude in a smaller vessel.
Electrostatic coalescer
An electrostatic coalescer is a pressure vessel with energised electrode grids, in which a high-voltage field coalesces water droplets in crude oil so they settle. Used without wash water it is a dehydrator; with wash water it is a desalter.
Crude oil dehydrator
A crude oil dehydrator is an electrostatic coalescer that removes produced water from crude oil to meet a water specification, usually stated as basic sediment and water. No wash water is added. It is the same equipment as a desalter.

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