Page 163 - Petroleum and Gas Field Processing

using either heat or chemicals followed by gravitational settling can break
some emulsions, but the process is dependent on the time spent in
coalescence. This time is the element that determines the equipment size,
hence its capital cost.

5.3.3 Treating the Emulsion
As explained earlier, using chemicals followed by settling can break some
emulsions. Other emulsions require heating and allowing the water to
settle out of the bulk of oil. More difficult (tight) emulsions require,
however, both chemicals and heat, followed by coalescence and
gravitational settling.
Basically, a dehydration process that utilizes any or a combination of
two or more of the treatment aids mentioned earlier (heating, adding
chemicals, and an applying electrical field) is used to resolve water–oil
emulsions [6,7]. The role of each of these aids is discussed next in detail.

5.4 HEATING

Heating is the most common way of treating water–oil emulsions. To
understand how heating aids in the resolution of water–oil emulsions and
separation of the water droplets from the bulk of oil, reference is made to
the droplet settling velocity equation derived in Chapter 4 [Eq. (7)]:

u ¼ 1:787 10 6 ð
Þd m ft=sec ð3Þ
o
where u is the water droplet settling velocity,
is the difference between
water and oil specific gravities, d m is the diameter of the water droplet (in
mm) and m o is the oil viscosity.

5.4.1 Benefits and Drawbacks of Heating
Heating of water–oil emulsions aids in the resolution of the emulsion and
the separation of the emulsified water in several ways. The most significant
effect is the reduction of oil viscosity with temperature. The viscosity of all
types of crude oil drops rapidly with temperature. From Eq. (1), such
reduction in viscosity results in increasing the water droplet settling
velocity and, thus, speeds and promotes the separation of water from
the oil.
As the water and oil mixture is heated, the density (specific gravity)
of both water and oil is reduced. However, the effect of temperature on oil

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