From Fossil To Fuel™
From Fossil To Fuel™

Episode 12 · 3 years ago

Episode 11 - Completion Types


Overview of the different styles and types of well completions.

My name is Brennan McDougall and I'm a professional engineer. Or the last decade I've worked in many different facets of the oil and gas industry. While I have a pretty solid technical background in oil and gas, I don't really know a whole lot about the other non technical departments that help run an oiling gas company. Recently I took a course to help develop my business acumen and better understand how the financial side of the business works. What a novel concept to educate the technical people on the business and financial side. I thought it would be a really cool idea to return the favor and educate the non technical people on the technical side. This is how the concept from fossil to fuel was born. Through these twenty four episodes, we will take a journey from how oil and gas was formed millions of years ago how it is refined into the fuel that runs our cars and keeps our homes. Come join me on this adventure as we learn how the oiling gas industry operates from fossil to a few we've already talked about hydraulic fracturing, which is one form of completion and tends to be the one that everyone hears about in the media, but it's one type. Generally speaking, completion is a type of design that takes the well from the state it's in after drilling to a state it needs to be in in order to produce the only gas. So really you're completing the well. You're taking it from a state where it can't do anything to a state where it can flow oil and gas and therefore completing well. That's why we call completions. completions can be very simple and they can be very complex. It really just depends on where your well is and really what you're trying to accomplish.

So we'll take a look at the most common types of completions, which are generally categorized into two categories, open hole or case whole. The difference is fairly simple. Open hole completions don't have any casing cemented in place in the production section. And just to revisit production section. So we're all on the same page here. When, if you recall from the drilling section that we talked about in earlier episodes, when you're drilling well, you drill surface section or with you that you have with surface casing. Sometimes there can be an intermediate section if you need it. And then there'll be a production section and since a lot of the wells that we drill nowadays are horizontal walls, meaning the last portion of the wall is horizontal, that horizontal portion is typically the production section. So to give you, I guess, a generic visual in your head what I mean by production section, think of the horizontal part of the will so finishing that earlier section. Open hole completions don't have casing cemented in place in the production or horizontal section, and case whole completions do. In some structurally competent and conventional formations, the production section might be left entirely bare, and we call this type of open whole completion a barefoot completion because it's the most simplest and most basic type of completion that we have. However, if you want any sort of flow control, you'll have to have some type of equipment down there to help you out. The main advantage to openhole completions is really just the cost savings, as you don't have to pay for casing or cement or any other type of equipment that you'd have to have...

...down there normally. You also don't have to pay for all the time and equipment it takes to put that stuff down whole in the first place. OPENHOLE completions can only really be used, though, when the formation is structurally competent, meaning that it can support itself with an open hole. So really what I mean there is that it's not going to collapse. So think about digging a tunnel. If you're digging a hole or digging a tunnel through the ground, if whatever you're digging through is structurally competent, meaning that it's not going to collapse on itself, then you can dig that tunnel without any sort of support. But if what you're digging through is not structurally competent, you're going to need some sort of support to keep it from collapsing on itself. And so we would never do an open hole completion in a formation or rock that is not structurally competent, because if you're going to leave that open, it's just going to collapse on itself, and now what was the point of doing that? So if it's not structurally competent, you pretty much have to run casing in place and that's what keeps the whole thing open. So openhole completions typically use what we call liners and open hole packers. So a liner's just a piece of metal pipe that is used in the production section or the horizontal section of the well. And so remember for casing generally speaking, when we have casing that runs all the way from, if we're talking the production section, all the way from the horizontal part up to surface where it lands in the wellhead, talked about that. In drilling section, liners will typically be only used in one portion of the well. So they don't run all the way up to surface. It'll just be for that section. So they typically,... an open hole design, will have either pre drilled holes or are slotted, and so to again, to try and give you a visual here, when I mean pre drilled holes, think of something like a cheese greater. A cheese creator will have all those holes in it that are pre jilled to slice or cut your cheese. Not that it serves the same function in this aspect, but to help you visualize what it would look like. It's kind of like a cheese greater where there's a whole bunch of holes that are pre jilled in the actual metal Piper or the liner. The slotted version, again for a visual is more like a flower sieve or a strainer that you would use in your kitchen. So same purpose, but just different designs. Either way, you need a way for the oil and gas to get from the rock or the formation into and through the liner so it can flow up the casing or tubing to surface. This means there needs to be some sort of holes in the liner. But remember that we don't have any cement in an open hole completion, so there's nothing really isolating the rock or sound or formation. As the oil and gas is produced, it's possible for small pieces or chunks of rock and or sand to flow out of the reservoir with the oil and gas and into the casing. This can pose a lot of problems. The debris could potentially pile up inside the casing and eventually plug the well and shut down production entirely. That is not good. It can also make the production fluid abrasive. If you're flowing oil and gas up your well with sand in it, it's like rubbing sand paper on the inside of your casing. Just not a good thing. Eventually it'll wear through and you've got a breach in your casing and or your tubing to deal with. Even if it makes it to surface. If you don't have surface facilities capable of handling sand,... can wear that out too, and fairly quickly. Therefore, it's very important in open hole completions to consider sand control. It's also important in case Hohole to but much more important in open hole because you're starting off with nothing between you and the formation. Like with open hole completion technologies, there are many, many different options. We're only going to cover the more basic and most common ones here. will do the same for sound control. Sand controls typically accomplished by using slotted liners or screens. Think of them kind of like a coffee filter. The liquid can pass through, but the majority of the solids won't. So essentially, when we're talking about slotted liners and screens, picture a really long cylindrical metal coffee filter along the entire length of the production whole section, horizontal part. Like coffee filters, slotted liners and screens can eventually fill up. Will eventually fill up. I guess they'll have to be cleaned out or replaced. This is just part of the regular maintenance cost associated with producing the well. If you're going to be fracking an open hole, you can use what are called open hole packers to help you out. If you've got let's say kilometer of open hole that you need to frack, you could potentially try to do the whole thing at once, but fluid tends to take the path of least resistance, which means you frack a couple of parts of the open hole really well, but you wouldn't efficiently stimulate the entire length of the open hole. This is where the open whole packers come in. They're kind of like gates along the length of the whole open hole section. Keep them all closed and you can open one at a time and FRAC...

...that little section, then close it off and open the next gate and frack that little section, and on and on until you complete the entire open hole section. The packer itself basically involves a piece of rubber that can expand a seal off the open hole, providing pressure isolation. It's more expensive than just leaving the open hole as is, but if you think you can fract the reservoir more efficiently and get more oil and gas out of the wall, then your increased production will more than justify the cost. Let's take a look at case tole completions open hole completions have grown in popularity recently, especially in unconventional reservoirs, but case hole completions are still much more common because they are the tried and true technology and tend to be, generally speaking, more reliable. However, because you now have both metal pipe and cement isolating the oil and gas, you need to perforate through both the casing and the cement to provide access points for the oil and gas to flow into the well. Recall that we talked about perforating when we went through the hydraulic fracturing episode. perforating uses guns to create these holes. Now, to clarify, we do call them perforating guns, but they don't actually use bullets or projectiles to create the holes. They actually use an explosive charge called a shape charge. The technology comes from the military, where it was used in anti tank weapons to Pierce tank armor. The explosive charges are physically shaped in a way so that when they explode, they concentrate their explosive energy into a high velocity jet which is sort of shaped like a carrot, or or at least the the cartoon style of Carrot. I guess most of this jet initially travels at hypersonic speeds up to...

...fourteen kilometers per second at the tip. This is over fiftyzero kilometers per hour or over thirtyzero miles per hour. Temperatures of this explosive jet can easily reach four to five hundred degrees Celsius. You can imagine it's not too hard for these charges to penetrate a few inches of metal and cement. It's pretty cool stuff. Anyways, back to caseful completions. Once you've perforated the casing, you have a couple of options. You can use the plug and perf method that we talked about in the hydraulic fracturing episode, but you can also use a packer system like we talked about for open hole completions, only this time the packers are cemented in place. The last thing we should mention about completions is the production packer and tubing. In case you didn't know, tubing is the same as casing in the sense that it's metal pipe, but it's the smallest metal pipe in the well, typically only a couple of inches in diameter. So the tubing, even though it's effectively the same as casing, being that they're both metal pipe, it has a different name because it has a different function. The reason we use tubing is to help the well produced better. For the main reason, as the well produces oil and gas, the reservoir starts to lose pressure over time. The reservoir loses enough pressure that it becomes harder and harder for it to push oil and gas up the well because, remember, the reservoir has to have enough pressure to not only push the oil and gas out into the well, in some cases it's got to push it up several kilometers up through casing and tubing before it even gets to the surface. So, in terms of a visual, I guess I seem to love these visuals. When we were kids, we used to play with super soakers all the time, the water guns that you would pump up and spray each other with. It's kind of the same thing with a reservoir. So...

...if you start off with your supersilker and it's all pumped up and charged full of pressure, as you pull the trigger and you start shooting the water out, eventually you start to lose your pressure and over time you basically run out a pressure and there's no water that comes out. It's the same kind of thing with an oil and gas reservoir. So unless you have a method of charging the reservoir back up, which we can talk about in a later episode. Water flooding would be an example of that, but we won't talk about that here. So unless you have a method of charging the reservoir back up, it's going to keep losing its pressure and eventually it's going to get to a point in time where it gets harder and harder to push that oil and gas up the OH. So at that point you can decide to install tubing and really what you're doing is you're effectively shrinking the diameter and therefore the flow area of the pipe that the oil and gas flows up. So I'll give you another analogy for this now. So think of a garden hose. What happens when you put your thumb partially across it? The water coming out goes way faster and way further. By reducing the flow area, you're able to increase the velocity of the water. It's just basic physics. That's exactly what we're doing when we install tubing, or well, typically it's the main reason. Like the packers I just mentioned, production packer uses an expanding piece of rubber to seal off the inside of the casing. You would typically only use a production packer if you had tubing inside you. Well, the tubing comes out of the top of the packer so that the oil and gas flows up the casing until it hits the Packer, at which point it flows through the packer and into the tubing. Because the packers been sealed up on the outside,...

...the oil and gas can only flow up through it and into the tubing. So what we've effectively done is isolated the casing above the packer. This is the second main reason why we install tubing to protect the casing. Sometimes Times oil and gas has corrosive chemicals in it. Well, a lot of the time oiling cast has corrosive chemicals in it. We can protect the casing by using the tubing as a sort of sacrificial lamb. As the tubing wears out, we can pull it out and change it with new tubing because, remember, if you're casing is cemented in place, it's going to be a lot harder to pull damage casing out of the well then it is with tubing. If you can just pull tubing out of the well and put it back in, fairly easily. As the tubing wears out, we can pull it out and change it with new tubing. The production packer is just what anchors the tubing and it's what isolates the casing above it. Hey guys, if you like today's episode, make sure you subscribe to the podcast. Unlike most podcasts that release an episode every week or two, I did all twenty four at once, Netflix style, so you can listen to them all right now if you just hit subscribe. If you like today's episode, make sure you leave me a comment or thumbs up, or you can email me at from fossil to fuel at GMAILCOM, or look me up on Linkedin. I'm Brendan McDougall.

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