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5
Emulsion Treatment and
Dehydration of Crude Oil
5.1 INTRODUCTION
The fluid produced at the wellhead consists usually of gas, oil, free water,
and emulsified water (water–oil emulsion). Before oil treatment begins, we
must first remove the gas and free water from the well stream. This is
essential in order to reduce the size of the oil–treating equipment.
As presented in Chapters 3 and 4, the gas and most of the free water
in the well stream are removed using separators. Gas, which leaves the
separator, is known as ‘‘primary gas.’’ Additional gas will be liberated
during the oil treatment processes because of the reduction in pressure and
the application of heat. Again, this gas, which is known as ‘‘secondary
gas,’’ has to be removed. The free water removed in separators is limited
normally to water droplets of 500 mm and larger. Therefore, the oil stream
leaving the separator would normally contain free water droplets that are
500 mm and smaller in addition to water emulsified in the oil. This oil has
yet to go through various treatment processes (dehydration, desalting, and
stabilization) before it can be sent to refineries or shipping facilities.
This chapter deals with the dehydration stage of treatment. The
objective of this treatment is first to remove free water and then break the oil
emulsions to reduce the remaining emulsified water in the oil. Depending on
the original water content of the oil as well as its salinity and the process of
dehydration used, oil-field treatment can produce oil with a remnant water
content of between 0.2 and 0.5 of 1%. The remnant water is normally called
the bottom sediments and water (B.S.&W.). The treatment process and
facilities should be carefully selected and designed to meet the contract
requirement for B.S.&W. Care should be taken not to exceed the target oil
dryness. Removal of more remnant water than allowed by contract costs
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.