Page 170 - Petroleum and Gas Field Processing

separation of the water droplets, which flow countercurrent to the oil flow
and collects at the bottom section of the tank.

5.5 CHEMICAL TREATMENT

As mentioned earlier, some oil emulsions will readily break upon heating
with no chemicals added; others will respond to chemical treatment
without heat. A combination of both ‘‘aids’’ will certainly expedite the
emulsion-breaking process [5]. Chemical additives, recognized as the
second ‘‘aid,’’ are special surface-active agents comprising relatively high-
molecular-weight polymers. These chemicals (deemulsifiers), once adsorbed
to the water–oil interface, can rupture the stabilizing film and/or displace
the stabilizing agent due to the reduction in surface tension on the inside
of the film (i.e., on the water side of the droplet). In other words, when the
deemulsifiers are added to the oil, they tend to migrate to the oil–water
interface and rupture the stabilizing film, as depicted in Figure 13. A
deemulsifier, as it reaches to oil–water interface, functions in the following
pattern: flocculation, then film rupture, followed by coalescence. The
faster the deemulsifier reaches the oil–water interface, the better job it
achieves. Figure 14 illustrates these steps.

5.5.1 Selection and Injection of Chemicals (Deemulsifiers)
The very first step for selecting the proper chemical for oil treating is
testing an oil sample. The representative sample is measured into a number

Figure 13 Action of chemical agents in deemulsification of water drops.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.