Page 6 - Treating Oilfield Emulsions

Segment 1 Chapter 3

Emulsions and Production Practices
Petroleum Extension-The University of Texas at Austin
A s oil and water are produced from a well, if the best method for avoiding a tight, difficuIt-to­

an emulsifying agent is present and if agi­ treat emulsion is to minimize agitation.
tationofthis combination ofwell fluids occurs, an The amount of water that disperses in oil with
emulsion will form. Once an emulsion forms, it a given amount ofagitation depends on the rela­
may remain loose and be relatively easy' to treat tive amounts of the two liquids. If there is not
or it may, because of the way in which it is much water, not much agitation is needed to
handled in the production system, turn into a disperse it in the oil. Conversely, if there isa lotof
stable and difficult-to-treat emulsion. Unfortu­ water, a lot ofagitation is needed to disperse it in
nately, manyother problems occur besides those the oil. If there is a lot of water in an emulsion
involving emulsions, and sometimes the action being agitated, the emulsion tends to break down
required to solve those problems maynotbeideal because the large numberofwater droplets in the
for preventing the formation of tight emulsions. emulsion strike each other frequently, coalesce,
Instituting new methods orinstallingnewequip­ and fallout. Therefore, less watergets dispersed,
ment just to minimize the formation of tight, and the stability of the emulsion is reduced. It is
stable emulsions is, however, frequently not eco­ possible, in some instances, to reduce treating
nomically justifiable. Operators must formulate difficultiesbyaddingwater to the well fluid ahead
production techniques by taking into account all of the point ofagi tation. This procedure is used in
factors, not merely those that pertain to emulsion relatively few cases, however.
problems. A free-water knockout-a vessel that removes
Each oil well has its own characteristics and free water from the well fluid~y be placed
offers individual problems, but previous experi­ ahead of the point of agitation. This works very
ence on similar wells often indicates a solution. well if the well fluid is easily separated into free
Trial and error, however, is sometimes the only oil and water; however, this procedure could
way to find the cause or to minimize the forma­ have a detrimental effect if the presence of excess
tion of a difficult emulsion. Some general prac­ water makes the emulsion looser.
tices are available, however, that, if followed, can
reduce oil-and-water emulsification. Minimizing Stable Emulsions
As mentioned before, certain conditions must in Flowing Wells
exist before an emulsion can form: (1) the liquids
must be immiscible; (2) sufficient agitation must Violent agitation of oil and water being pro­
occur to disperse one liqUid as droplets in the duced in flowing wells causes water droplets to
other; and (3) an emulsifying agent must be pres­ disperse in the oil and leads to the formation of
ent to stabilize this dispersion. In oil production, very stable emulsions, which are often difficult to
all of these conditions frequently occur. In some treat. Such agitation is caused primarily by gas
cases, however, it is possible to minimize, if not coming out of solution as pressure is decreased
prevent, two of the three conditions. Since treat­ and by turbulence that occurs when production
ing is done to disrupt or counteract the effect of flows through restrictions, fittings, and sharp
the emulsifying agent, either (1) water and oil bends in the tubing and lead lines.
must not be produced simultaneously, or (2) any
agitation great enough to form a more stable Surfa~ Chokes
emulsion must beavoided. Water production can When a surface choke ora back-pressure valve
sometimes be reduced, if not eliminated, by is used to control production, most of the emul­
remedial cementing procedures, such as plug­ sion is formed immediately downstream from it.
ging back the wellbore, so that the production is Upstream from the choke or the valve, pressureis
withdrawn from a point higher in the reservoir. relatively high compared to that on the down­
Because it is usually very difficult to exclude stream side. (Higher upstream pressure can be
water from the wellbore completely, however, confirmed by noting that tubing pressure at the

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