What is an Oil Emulsion?

What is an Oil Emulsion?

What is an Oil Emulsion?

Emulsions are mixtures of oil, water and an emulsifying agent.

They are almost always very fine droplets of water dispersed, or mixed into, crude oil. The quantity of water droplets dispersed in an emulsion is usually less than 10%. Other common examples of emulsions are homogenized milk, shaving cream, and mayonnaise.

Occasionally, an emulsion occurs that contains droplets of oil dispersed in water. This is called a “reverse emulsion.”

How are Oil Emulsions Formed?

Emulsions normally do not exist in the producing formation but are formed when oil and water are produced together with a great amount of agitation. When water and oil in a reservoir enter the wellbore through the perforations in the casing, comparatively large pressure differences are created which violently mix the produced oil and water together, so that an emulsion forms.

In traveling up the tubing more mixing and agitation takes place. It is intensified by the release of gas bubbles as the pressure reduces as the fluids move up the tubing.

Upon reaching the surface, even more violent action takes place as the fluids pass through a choke. Violent mixing is even more pronounced in pumping or gas lift wells.

In appearance, the emulsion resembles neither oil nor water. For example, a dark green crude oil when emulsified will often appear a muddy brown color.

Generally, the viscosity of the emulsion is higher than the viscosity of the oil or water. In other words, the emulsion is thicker and will not flow as readily as oil or water. It may have a fluffy appearance and feel, which is caused by gas bubbles trapped in the emulsion.

If the emulsion is viewed through a microscope, a great number of tiny spheres of water can be seen mixed throughout the oil. Each of these tiny spheres is surrounded by a tough film. This film is a layer of emulsifying agent, and it prohibits the droplets from bumping into one another so they can coalesce.

The agitation caused by the production of oil and water together is the basic cause of emulsion. This is the reason emulsions are not found in the producing formation.

Not all of the salt water produced with the oil is emulsified. The water that is not emulsified is known as free water. Free water will settle quite readily from oil.

In fact, if the produced fluids are allowed to stand in a vessel for a short period of time, three distinct layers will form.

  1. On the bottom will be free water.
  2. On top will be clean oil.
  3. In the middle between these two elements will be a layer of emulsion.

This middle emulsion layer will often remain as an emulsion indefinitely.

An emulsion composed of extremely small droplets that shows no tendency to separate into water and oil is known as a “tight” or “stable” emulsion. If it is composed of droplets which shows a tendency to separate, it is known as a “loose” or “unstable” emulsion.

Emulsifying agent creates a film around water droplet and hold it in the oil. The film must be destroyed in order for the water droplets to coalesce and fall out.

Treating Methods for Oil Emulsion

Anything which tends to weaken the film surrounding the water droplet will try to destroy the emulsion. There are four things that producer use to break the emulsion:

  1. Chemical action on the film.
  2. Heat to weaken the film, change the effective weight of water and oil, and reduces oil viscosity.
  3. Electricity, causing the droplets to smash into each other
  4. Scrubbing action

When the emulsion is broken by weakening the film, the water droplets coalesce to form bigger drops, which will settle to the bottom because water is heavier than oil.

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