How a Free Water Knockout Works | Podcast Episode #15

In this episode we are joined by Kyle Andrews, Product and Applications Trainer at Kimray, who explains how a free water knockout works. 

Topics in How a Free Water Knockout Works

  • What is “free water”?
  • Why is water management important?
  • What are sacrificial anodes?

oil and gas podcastblock and bleed valvedouble block and bleed procedure

Curtis: Hello, and welcome to Stuff You Should Know about Oil and Gas Production. I’m your host Curtis Winkle here with Kyle Andrews, product and applications trainer for Kimray.

The topic we’re talking about today is how a free water knockout works. This is a very common, important piece in oil and gas production upstream. So why don’t we start with water. Why is water present? What are producers’ options for dealing with it?

Kyle: Water is always a byproduct of oil and natural gas. When are you talking about what’s coming out of the earth, the emulsion, water is part of that—water, oil and gas are all mixed together and you’ve got to remove the water from both the oil and the gas to make those things valuable.

Curtis: And depending on the region, there could be a lot of water, right?

Kyle: The ratio of oil to water can vary. In certain places, the ratio can be 100 to 1. So, for every barrel of oil that you are getting out of ground, you have to deal with 100 barrels of water. That is a lot of water to just to get that one barrel of oil.

Curtis: Yeah, for sure. So, this free water knockout, talk a little bit about that. What is it, how is it used? What is it for?

Kyle: Its main purpose is to knock out (separate) the free water that’s in the oil emulsion.

This piece of equipment is usually large because of volume of the free water. The more time fluid can spend in this vessel, the more separation you will get. The free water is going to be separated from the oil and gas easily, that is why it’s called free water.

This would be the first piece of equipment, that the fluid enters, and there would be equipment downstream of it that further separate the water and gas that’s entrained in the oil. But this is going to knock out that free water.

Curtis: Is it usually one well or more than one coming to these things?

Kyle: It could be one well, it could be a multiple wells depending on the area and the location.

Curtis: How big do they get?

Kyle: They can range from 5’x20′ to 10’x30′. It just depends on the volume of liquid going through them and the number of wells going into it.

Curtis: Gotcha. So, you talked a little bit about what this vessel does. What are the advantages of it? What are the benefits? Why do people use this vessel specifically right out of the gate?

Kyle: If you do have a high water-to-oil ratio, if you were to use let’s say a heater treater to treat that fluid, to help separate, you’re going to be spending a lot of money on a fuel to heat it. And heated vessels are more expensive to manufacture. So, it would just get a lot more expensive.

It is more cost effective to build free water knockouts. And so, you are saving money in the long run by having an extra piece of equipment to get rid of majority of the water before you then heat the emulsion to help that all separate.

Curtis: Are they always necessary?

Kyle: No. It depends on your water-to-oil ratio. If it calls for it and it’s going to be more cost effective for you to have this piece of equipment on location, then that’s when you’ll have one made and use it, but it’s not always necessary.

Curtis: Okay, let us jump inside one of these things. So, the well stream is coming into the free water knockout. What is happening inside there?

Kyle: The well stream enters the vessel. Usually there will be a diverter plate. As soon as the fluid enters the vessel that impact with the plate changes the direction. That helps start the separation process

Then you will have a wave breaker or a baffle almost in the middle of the vessel. What that does is keeps things from splashing around too much. It settles the flow of the liquid through the vessel and that helps it separate.

If it’s really turbulent inside the vessel, that’ll keep the emulsion in an emulsion. It won’t let it settle and separate out. So, you want to slow down that flow to get it to separate out.

Curtis: Any troubleshooting tips for these free water knockouts? Maybe it’s not, you know, separating well, or your controls aren’t working, right?

Kyle: Yeah. The biggest one would be just the size of the vessel.

If your vessel is undersized and it’s not large enough to get the separation you need for the amount of volume going through it, you’ll get a lot of carry over. A lot of that free water will still be with the oil and will be carried over to the next vessel, which is typically a heater treater. That’s going to cause issues for that heater treater. You are going to have to get it a lot hotter, use a lot more fuel to heat it.

So really, getting the correct size vessel is the biggest thing.

Curtis: I’ve been out before and seen multiple free water knockouts on one site. Why would someone need more than one?

Kyle: So when we’re talking about a CTB, or a central tank battery, where multiple wells are coming into one location, they’ll have a production vessel, which is the largest because that’s what multiple wells will be going into.

But if a producer wants to test a single well, they’ll usually have a smaller vessel—still a free water knockout, but just much smaller—on that same location. They can test individual wells to see what they’re producing and see if the wells need work or if they need something done to them to improve production.

Curtis: I see. What about one of my favorite named pieces in the world—”the sacrificial anodes”?

Kyle: So, there could be two, maybe three anodes depending on the size of the vessel. They are called sacrificial because the salt water that’s swirling around in this vessel is creating static electricity, and that’s very corrosive.So, it will eat away at the shell of the vessel, which you do not want. These sacrificial anodes are installed and they’re made out of aluminum or magnesium.

So, it’s basically offering this sacrificial anode to the corrosive, saltwater and static electricity inside the vessel, and those will be eaten away instead of the shell of the vessel.

Curtis: And is that because the material attracts the static electricity?

Kyle: Yeah, basically. It is that softer material is easier for that static electricity go to and eat away at than the steel of the vessel. The static will take the path of least resistance.

Curtis: All right. Well, thanks for your time, Kyle, for explaining how a free water knockout works.

You’ll find links to the products and resources we mentioned in this episode in the show notes, and we’ll catch you next time on Stuff You Should Know about Oil and Gas Production.


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