Demulsifier
- Also known as
- emulsion breaker, demulsification
A demulsifier, or emulsion breaker, is a chemical used to separate an emulsion into its oil and water phases. In oil production it displaces the natural film that stabilizes water droplets in crude oil so the droplets can merge and settle out.
What is a demulsifier?
Oil and water produced together from a well often form a stable emulsion, usually water droplets dispersed in oil. Natural components of crude oil, especially asphaltenes, resins and fine solids, collect at the droplet surfaces and form a tough film that keeps the droplets from merging. A demulsifier is a surface-active chemical that breaks that film so the water can separate.
How demulsifiers work
Demulsifiers are designed to migrate quickly to the oil-water interface and displace the natural stabilizers. Once the film is weakened, water droplets can:
- Flocculate, clustering together.
- Coalesce, merging into larger drops.
- Settle, separating from the oil by gravity.
Most commercial demulsifiers are blends of polymeric surfactants, such as alkoxylated resins and block copolymers of ethylene oxide and propylene oxide, formulated to act quickly and to leave a clean water phase.
How demulsifiers are used
Demulsifiers are usually injected upstream, at the wellhead or before separation equipment, so they have time to work. They are used together with physical treatment: heat, which lowers oil viscosity; residence time in separators and treaters; and electrostatic grids, which help droplets coalesce.
Selection is typically done by bottle tests, which compare candidate products on the actual produced fluids for speed of separation, clarity of the water and dryness of the oil. Because produced fluids change over a field’s life, programs are re-evaluated periodically.
Reverse emulsions
When oil droplets are dispersed in produced water, the emulsion is called a reverse emulsion. It is treated with water clarifiers, or reverse emulsion breakers, so the water can be discharged or reinjected and the oil recovered.
Frequently asked questions
An emulsifier stabilizes an emulsion; a demulsifier breaks one. Both are surface-active, but they are designed to do opposite things at the oil-water interface.
Natural surface-active components of crude oil, such as asphaltenes and resins, form rigid films around water droplets, and fine solids can reinforce them, so droplets resist merging without chemical and physical treatment.
Sources
- demulsifier; emulsion breaker, SLB Energy Glossary
- Emulsions in oil production, SPE PetroWiki