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From Fossil To Fuel™
From Fossil To Fuel™

Episode 15 · 2 years ago

Episode 14 - Wellheads

ABOUT THIS EPISODE

A high level overview of the different components and what they do.

My name is Brendan 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 to 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 Keats our homes. Come join me on this adventure as we learn how the oiling gas industry operates from fossil to a few...

...think of the Faucet on your kitchen sink. It's a pretty important piece of equipment in your house. It gives you access to water whenever you want it, with however much you want. You can open it a little bit or you can open it all the way, depending on what you're doing. This is almost exactly what a wellhead does. If we simplify its purpose, a wellhead is basically a tap or Faucet for the well. Its main purpose is also to provide a means of suspending, casing and tubing the metal pipe inside or what becomes the well, while also containing pressure, just kind of how...

...like the Faucet on your sink connects to the water pipe below it and holds back pressure from the water. Recall when we talked about drilling that the drilling rig drills different sizes of holes. The surface hole is the biggest, and then as they get progressively smaller, you're getting deeper because the deeper strings have to fit inside the shallower ones. So, for example, you could have a five and a half inch production casing string inside a seven and five eights inch intermediate casing string inside a nine and seven eights inch surface casing string. So that means you'd have three casing strings, all terminating at surface and they terminate in the well head. So think about how much several thousand feet or several thousand meters of metal casing waste. It's a lot and most of this...

...weight is hanging on the inside the wellhead, meaning it's pulling the well head down. You've got all this weight pulling it down. So the wellhead needs to be really strong and properly engineered for whatever casing system you're running. This can be done in several ways, but typically it's done with what is appropriately called a hangar or in some cases, a dog net. The hangar is like the cap that goes on the top of each casing string. The hangar itself will have some sort of lip or extended edge that's going to sit or rest on a shoulder or a lip inside the well head. So if you picture picture a screw landing or putting a screw inside a screw hole, so the body of the screw passes through the hole but is held in place by the head of the screw or the flap part at the top of the screw. It's the same kind of thing with the hangar. So as you're casing...

...is going through through the well head, the metal pipe, I mean so the metal pipe passes through the hole and once you get it to the point where you've gone as far as you need to. The top part that we now put on, or the Cap, is what we called a hangar, and so that hangar, as you're coming through the wellhead, is kind of like the top of the screw and it's going to sit on a lip inside the well head and by sitting on that lip it's going to be holding all of the weight of the casing string below it. So it's the same kind of thing we talked about with the screw. Hopefully that'll help visualize in your head what the casing hanger does inside the Wellhead. So while the oil and gas will typically come up the production casing string or possibly a tubing string, you'll want to have access to the annualist or the spaces between each casing string.

So wellhead will also enable you to do this and we'll have several smaller valves coming off the side of it to provide access points for these ANNULI. Now I'm not going to go into detail about little pieces and components of a wellhead because, frankly, I just don't think you need to know. I've taken a week long course on just wellheads that goes into all the details on seal sports, mechanical pieces, metallurgy. So we could go on for a while here, but like everything else in this podcast, let's just stick to the basics and then need to know type of stuff. wellheads are very important, though, and are surprisingly overlooked. Not Too many people, even on the engineering side, can tell you a lot about wellheads other than their basic functions. There's a ton of engineering that goes into designing them, though, and it's because the casing strings aren't all installed at once. You need to...

...consider how they're going to be installed in the wellhead, especially because they're different sizes. And this is just for basic drilling designs. Some will have complicated designs and lots of offshore wells will have subsea wellheads, which means the wellheads are located at the bottom of the ocean. At least with surface wellheads you can actually touch them and feel them. So, just like the Faucet, the wellhead has valves that open and close to contain pressure and chokes that control the flow of the well. So a choke, if you've never heard of that term before, I think in some of the previous episodes I've used the example of a garden hose, where if you put your finger over part of the garden hose it makes the water shoot farther. Essentially what you're doing is reducing the surface area to flow to increase your velocity of the fluid. It's...

...not to go too deep into physics here, but hopefully you follow what I'm talking about. But essentially what you're doing is you're choking off part of the fluid with your thumb, and so a choke is effectively reducing the area to flow. And so if you think about your thumb on the garden hose, as you're putting part of your thumb over the mouth of the hose, there's less area for the water to flow out and so therefore it's velocity is increase. So if we have a choke in a pipeline or we have a choke in a wellhead, it's basically doing the same thing. It's reducing your flow area. The tap on your kitchen sink or bathroom sink typically only has one valve, but due to much higher pressures when dealing with oil and gas, most wellheads will have to or even three main valves. These main valves are known as the master valves. The one on the bottom is fittingly called the...

...lower master valve, and the one on top of it is called the upper master belve. So ninety nine percent of the time the upper master valve is the one that's used as the working valve. When I say working valve, what we mean by that is that's the valve that we operate. So if we're opening and closing valves on and off, on and off, we're not going to use the lower and then the upper or the upper and then the lower. Will only use one and that one is called the working valve. And in this case most of the time, if not all the time, it's the upper master valve. And this is because if anything happens to the upper master valve, whether it gets eroded or it stops working or it seizes up and you need to change it out, you can still close the lower master valve and isolate pressure below it while you change out the upper master valve or anything above it. On the contrary, if you were to use the lower master valve as your working valve and it failed now if you need to...

...change it out, there's no easy way to isolate the wells pressure below it so that you can change it out. So this is why we use two valves, and oil and gas, then only one in your house, although, yes, your house does have a main water shut off valve two. But essentially we'd have two valves in oil and gas stact on on top of each other and one is basically a backup. Most people who are listening to this have or have had leaking tap at some point. Some people change out the valve cartridge, cartridge in the Faucet or whatever it is. That when you would change out the valve to stop the leak, and some maybe are comfortable leaving a slow drip well. That might not be a big deal in your house. If you're leaking a slow drip of oil onto the ground, that's a big deal because now you've contaminated the ground. It's important that your...

...valves are in proper working order and that the different components of the wellhead are assembled properly. I should probably make a couple of differentiations here before we wrap up. When you talk about wellheads, most people tend to assume that you're talking about the whole metal stack that sticks up out of the ground, and so anybody who googles a picture of oil and gas if you're seeing the metal stack or the the metal valves that are above ground. This is what most people would think about when I say the word wellhead. So I should clarify, though, that while wellhead tends to be an all encompassing term, technically speaking the wellhead is only the piece of equipment that provides the suspension point and pressure seals for the casing strings, the master valves and everything above, which is what most people actually see in their head and think of as a wellhead,...

...is actually known as the Christmas tree, or sometimes just the tree or production tree. So, going back to when we first started this episode, I should correct myself and saying that it's the Christmas tree and not the well head that actually controls the flow coming out of the well, because it's the Christmas tree that contains all of the main valves. The wellhead is just what houses the tops of the casing strings. Remember, these are the casing hangars. The hangars suspend the weight of the casing but also provide a seal so that oil and gas can't leak out of the well head. A lot of wells will run a tubing string inside the production casing. Kind of talked about that a little bit already, but will get more into why this happens in episode nineteen. But typically the top of the tubing string or the tubing hangar does not actually reside in the well head, and we'll get into details as...

...to why that is, but it has to do with the operation happening at the later time. But as a result, a tubing head is attached to the top of the well head for the tubing hangar to sit in its purposes effectively the exact same as well head, but it's run as a separate piece of equipment and is therefore designated with a different name. So let's recap for a basic well. So you have your casing and tubing strings coming from below ground what, at whatever depth they are, and they're coming back up to surface. So the casing strings will come all the way to surface, they'll terminate in the well head and are locked in place and hanging by the casing hangars. The tubing head sits on top of the well head so that the tubing string can come up through the production casing come up through the well head and then the tubing hangar, which is at the top of the tubing string,...

...can land inside the tubing head, and I guess, just if you haven't heard this term before and I may have already used it today, apologize if I didn't clarify what it was. But when we say land something, it means for something to sit on. So if I'm saying land the tubing hangar or land the casing hangar, what I mean is the final action of that casing hangar or tubing hangar sitting on the shoulder or the lip inside the well head. So it's actually coming down and making contact with that lip. That that action, that final action of it's sitting there. Is What we mean when we say landing the tubing hangar or casing hanger. So we've landed the tubing hangar inside the tubing head and on top of the tubing head or the master valves, which is where the Christmas tree starts, and on top...

...of the master valves is the rest of the Christmas tree which, depending on what you're doing, is various configuration of smaller valves that can provide access to the well. 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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