Page 7 - Treating Oilfield Emulsions

Segment I Chapter 4

The Basic Principles of Treating
Petroleum Extension-The University of Texas at Austin
F or purposes of this manual, treating refers to

any procedure designed to separate foreign
matterfrom crude petroleum.Foreign matter may
include water, salt, sand, sediment, and other
impurities in oil; paraffin wax and asphaltenes
are not considered impurities here. Basically,
treating involves allowing time for water to settle
out of an emulsion and be drained off. Settling
time and draining are accomplished in various
mechanical devices such as gun barrels (wash
tanks) and free-water knockouts. To speed up
settling time, oneormore of the following proce­
dures may also be used: Figure 10. A photomicrograph of a water droplet in a
water-in-oil emulsion. Note that the rigid film sur­
1. applying heat; rounding the water droplet looks like plastic wrap.
2. applying chemicals;
3. applying electricity; and
4. adding diluents to reduce viscosity.

Factors Influencing Treating
The factors involved in treating water-in-oil
emulsions include breaking the films surround­
ing the small water droplets, coalescing the drop­
lets to produce larger drops, and allowing the
water drops to settle during or after coalescence.
In theory, all emulsions separate into oil and
water if allowed to settle for an unlimited time.
Indeed, a considerable amount of water pro­
duced with petroleum does separate without the
assistance of heat, chemicals, or other devices.
Figure. 11. A photomicrograph of a water-in-oil
However, the small water particles in water-in­
emulsion showing two water droplets touching but
oil emulsions are usually surrounded by a tough unable to merge because of film around the droplets.
film that gives the appearance of plastic wrap
when viewed under a microscope (fig. 10). This
film resists being broken, and, until it is broken,
the water droplets cannot coalesce-at least, not
in any reasonable length of time (fig. 11). There­
fore, heat, chemicals, electricity, mechanical
devices, and various combinations are normally
required to cause the film around the water drop­
lets to break and coalesce (fig. 12).
It should be emphasized that no two oilfield
emulsions are alike. The procedures used to treat
the emulsion produced from one field almost
never work on an emulsion from a different field. Figure 12. A photomicrograph ofa single water drop­
In fact, the emulsion produced from individual let in a treated emulsion. Note that the film is break­
wells within the same field sometimes varies. ing.

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