Borehole Completion Methods and Casing Options
Borehole completion methods and casing options
Your project manager is going to design your well in a way that works best with your aquifer and the type of well system that you need. There are three decisions that we will consider for your well. The first is the type of casing. Here are the options that we offer.
PVC Casing is most commonly used on residential wells or small commercial wells. It is great because it resists corrosion and is easy to install. But it is limited in the collapse pressure rating. So, we must be careful to use the right grade of pipe for your well. If the well is too deep for sdr-17, we will use sch. 80 pvc.
Steel casing is used for our large commercial wells and for deep applications. Steel is very strong and can handle heat stresses. But steel rusts over time so we have to understand that over time, the casing will rust.
Fiberglass casing is an alternative that we really like. It is very strong, handles heat up to 300 degrees, and does not deteriorate over time. We can get it made to any strength requirements and it is fairly easy to install.
The second decision is to choose a completion method. We have three methods to choose from. This is a big decision because this is how we connect our casing to the aquifer. If we do it right, we get all the water that the aquifer can provide, while limiting the amount of sediment that comes in. And the method that we choose will depend upon the type of casing you are using as well as the conditions of the aquifer. Here are the main options.
Open hole completion is a where we don’t install any casing in the production zone. The casing might only extend part of the way into the borehole, or it might go all the way down to the top of the production zone. The main point is that the production zone is expected to stand open without the need for any casing. This type of completion method is typically used in hard rock formations like granite. If there is no sediment visible in the water produced, these types of completions can be very effective. Furthermore, they are cheaper and give you the ability to clean out the well at any time.
Packer completion is used most commonly in most of our wells. For this completion method, we install casing all the way to the bottom of the borehole. We even have casing through the production zone. We install packers (seal made of neoprene) around the outside of the casing to seal between the casing and the borehole wall. We place the packers right in the top of the production zone so that the packer will seal off any sediment or bad water that we want to keep out of our well.
Gravel packing is used for wells that have a lot of sediment in the water. We have some aquifers that are filled with sand. We are trying to filter out that sand and just let the water flow into the casing. The best way to do that is with a gravel pack. We install our casing with a fine screen in the production zone. Then we put gravel down the hole to fill the space outside the screen. The gravel will trap the sand but still allow the water to flow into the casing. We have to choose the right size screen and gravel depending upon the size of the sand we are trying to stop.
The third decision is to choose the type of screen that we will install down in the production zone. If we have a hard rock formation that doesn’t produce much sediment, we typically just drill holes in the casing. But if the aquifer has sediments in the water, then we have to use a screen. Screens are fragile and can be expensive (depending upon the model) so we are careful to use these only when needed. Watch the video at the top of this page to see those issues.