Breaking Emulsions
In the beginning of this course you learned your job as a specialty oilfield chemical sales rep is to keep the oil and gas flowing and to make sure it’s salable. In this unit, you will learn about emulsions, which potentially threaten the production flow in both ways.
Contents
- 1 What is an emulsion?
- 2 How can emulsions affect production?
- 3 What causes an emulsion?
- 4 What is an emulsifying agent?
- 5 How do emulsifying agents create emulsions?
- 6 Once formed, is an emulsion permanent?
- 7 How are emulsions broken?
- 8 How do demulsifiers work?
- 9 What are Champion’s demulsifier products?
- 10 How are emulsion breakers applied to the production system?
- 11 References
What is an emulsion?
An emulsion is a combination of two immiscible liquids in which one of the liquids is dispersed as small droplets into the second liquid. The phase that is dispersed is called the internal phase. The liquid into which it is dispersed is called the external phase.
Emulsions can be:
- Water-in-oil (forward)
- Oil-in-water (reverse)
Not all emulsions are bad. Commercial products such as mayonnaise, peanut butter, some types of make-up, and paint are examples of useful emulsions.
How can emulsions affect production?
Emulsions can imperil production operations in two general ways:
1 Cause oil to be unsalable 2 Slow the flow of production fluids
The first case is caused by water-in-oil emulsions. Only a specified percentage of water can be contained in oil for it to be “in spec” for transport in a pipeline. If oil exceeds this specification, it either cannot be transported in the pipeline, or it has to be sold at less than top price. Oil that is “out of spec” because of its water content is called wet oil (also referred to as slop oil.) If a well is producing wet oil, it is typically stored in a large tank to be demulsified and then transferred to the pipeline. Unfortunately, these tanks have only a limited capacity. Although most emulsions will break on their own over time, if they do not break before the tank is full then production must stop.
Besides making the oil unsalable, emulsions can also slow the production flow. Emulsions are characteristically very viscous, making them thicker than base production fluids. This can cause the production flow to slow excessively because the fluid is so thick it cannot flow properly. Emulsions can also create friction in flowlines that will slow the production flow.
What causes an emulsion?
Emulsions are created when a thin film surrounds the internal phase (water), entrapping it in the oil so that it cannot readily break free. There are certain conditions that must exist for an emulsion to be able to form. Emulsions require:
- Two (2) immiscible liquids
- An emulsifying agent
- Agitation
What is an emulsifying agent?
Emulsifying agents (also called emulsifiers) allow a film barrier to form around the small water droplets dispersed in the oil phase. This barrier prevents the water from separating, or falling out, from the oil. Only minute amounts of an emulsifying agent (ppm) are needed for an emulsion to form.
Typical emulsifiers are:
- Clay
- Sulfates
- Sulfides
- Asphaltenes
- Wax
- Carbonates
- By-products of other chemical programs (e.g. – iron particles from corrosion)
- Surfactants from drilling and work-overs
How do emulsifying agents create emulsions?
Emulsifying agents are dual nature molecules. They consist of a hydrophobic end, which dislikes water, and a hydrophilic end, which likes water.
These properties cause the agents to concentrate where the oil and water meet (also called the oil-water interface) and form a barrier around the water droplet. Over time, more emulsifying agents will migrate to the oil-water interface and the emulsion usually becomes more stable and difficult to break. The layer that forms at the interface is called a rag layer.
Once formed, is an emulsion permanent?
Theoretically, an emulsion could remain stable for years. However, oilfield emulsions usually will separate with time. The problem is the producer seldom has the time to wait for the water to fall out of the oil. Additionally, the more stable the emulsion, the tougher it is to break.
The stability of an emulsion depends on:
- The emulsifying agent
- The viscosity of the fluids
- Specific gravity of the oil and water
- Amount of water in emulsion
- The age of the emulsion
- Amount of agitation present
How are emulsions broken?
There are several options available for breaking emulsions. Even though Champion’s business is selling chemicals, you should also be familiar with these other available options for treating oilfield emulsions.
To break an emulsion, the film surrounding the internal phase must be disrupted so that the water droplets can unite and collect in a layer separate from the oil. This can be accomplished with a chemical emulsion breaker, which is also called a demulsifier.
A demulsifier is usually a blend of several chemicals that give it hydrophobic and/or hydrophilic properties, which enable it to penetrate the stabilizing film that surrounds each water droplet.
Demulsifiers are used to:
- Dehydrate oil (remove the water)
- Desalt oil (remove solids)
Wet oil cannot be sold as “pipeline spec.” Oil that contains salts is often desalted because the salts can adversely affect the refining process.
How do demulsifiers work?
In a nutshell, demulsifiers work by weakening the film formed around the water by the emulsifying agents. It is a process that occurs in four stages, as illustrated in the table below.
The Four Stages of Chemical Emulsion Breaking
What are Champion’s demulsifier products?
Champion’s line of demulsifiers is marketed under the trade name Emulsotrons®. Because the nature of emulsions can differ from region to region, Emulsotron® products come in many formulations.
In spite of the many formulations, however, almost all demulsifier are designed with a polymeric “backbone” molecule. Ethylene oxide (EO) and propylene oxide (PO) are then added to the polymer molecule to increase the surfactancy and to change the way the base molecule is soluble in the emulsion.
Both EO and PO change the solubility of the demulsifier in the emulsion.
- Adding EO makes the demulsifier base more soluble in water.
- Adding PO makes the demulsifier base more soluble in the oil or condensate.
Some demulsifiers act faster than others. These faster acting products will drop the majority of water quickly, but may not completely dry the oil. It typically takes a blend of both types to thoroughly dry the oil and remove any salts. Sometimes, those demulsifiers that are fast waterdroppers can carry out of the vessel with the water, and therefore cannot continue working to dry the oil.
How are emulsion breakers applied to the production system?
Emulsion breakers are typically applied by continuous injection. However, batch application of water knockout products are sometimes used for problems in storage tanks. In these cases, the intent is to hit the oil supply with a large dose of chemical to quickly drop the water.
References
Treating Oilfield Emulsions (4th Edition). Austin: University of Texas Petroleum Extension Service, 1990.
