What is a Free Water Knockout (FWKO)?

What is a Free Water Knockout (FWKO)?

A free water knockout (commonly abbreviated as FWKO) is an oil and gas production vessel that separates the produced oil emulsion into its various elements.

What is “Free Water”?

Free water is water produced with crude oil that is not emulsified. Free water will generally settle out of the oil emulsion mixture if given time.

Producers remove the free water as soon as possible for three primary reasons:

  1. Free water overloads piping and equipment. It may be up to 50 or 60% of total production, depending on your region.
  2. Free water can be highly corrosive. Emulsions ordinarily are not corrosive because the water is dispersed in oil so only oil comes in contact with steel equipment. In other words, oil is the continuous phase.
  3. Free water costs more to heat. When heating the emulsion as a means of breaking it, water takes about twice as much heat as oil, driving up fuel costs.

This said, free water does have some benefits. For example:

  1. Free water carries heat. When produced in the tubing, oil, gas and water all start out at the same temperature, which is the reservoir temperature. Since water takes about twice as much heat as oil to raise it to a given temperature, a unit weight of water carries twice as much heat as oil. This means the water will carry reservoir heat farther downstream than oil, and it is therefore a help in eventually breaking the emulsion.
  2. Free water can facilitate “water wash.” When an emulsion is mixed with salt water, the washing action of the salt water has a tendency to break down the emulsion. This is called “water wash” and is incorporated into many treating systems.

How Does a Free Water Knockout Work?

A free water knockout separates the three elements of a well stream: gas, oil, and water. As the elements in the vessel separate, a liquid level controller opens a control valve to release the water downstream.

Another liquid level controller performs the same function for the middle oil emulsion layer.

Finally, the gas is released through the top of the vessel and sent downstream for further treatment, flaring, or to a sales line.

Depending on the pressure requirements, either a Back Pressure Regulator or High Pressure Control Valve is used to hold pressure on the vessel.

What’s the Difference Between a Free Water Knockout and a Separator?

A free water knockout is often referred to as a separator. It may be labeled “three-phase separator” as it separates gas, oil emulsion, and free water.

To speak with an expert about how we can help control your free water knockout, contact your local Kimray store or authorized distributor.