Drillers Have Optons for Installing Water Well Screens
In my last column, I talked at some length about selecting screen openings and then ended up by describing one installation method: just driving a pointed screen into a water-bearing formation. Now, I am aware that in this day and age many screens are either threaded or glued directly to the bottom of the casing in a rotary hole. This certainly works, but if the screen has the wrong openings or fails for some other reason either at installation or later, it is impossible to pull. I’m going to limit my comments to screens that can be pulled and would be used in a cable tool or hollow rod drilled well.
Probably the most popular method of installation is the so called telescoping method—sometimes called the pull back method. In this method, the casing is driven down through the aquifer to where the drive shoe is at the target depth for the bottom of the screen on installation. The casing is cleaned out and it is a good idea to move through the formation in step. That is, drive a foot, clean out and drive another foot, and clean out and keep doing this until we get as deep as desired. Just driving the casing, say 5 feet for a 5-foot screen and then cleaning out is not a good idea.
In any event, when we have reached final depth we will clean out the casing one last time and lower the screen to the bottom. If we are using a neoprene packer and the screen is fairly short we may have to push it to the bottom with our drilling tools. I’ll write more about fittings for our screen in another column. With the screen at the bottom of the casing, we will then retract the casing the length of the intake portion of the screen so it is telescoped out. How we pull the casing back will vary with conditions and depth. If we are down fairly shallow, say less than 100 feet, we may be able to just pull the casing back using our rig’s casing line. If we are down deeper or the casing is really tight, we may have to bump it back using a knocker-head, pipe pulling jars or a trip spear. If we are down really, really deep we may need to use a casing ring and powerful jacks. In fact, we may have to use jacks and a bumping method if our casing is super-tight. The method we use to pull the casing back is not really that important, only that we expose the screen to the aquifer as any openings left in the casing will do us no good at all.
Rig operators have multiple ways of sinking screen, including just driving it in, telescoping it in or bailing it in. Source: iStock
In my experience, it is a really good idea to hold the screen down while we are pulling the casing back. The tool string on a cable tool or the drill pipe on a hollow rod machine can be used for this purpose if we are pulling back with the casing reel or the casing ring. If we are bumping back, we can use a couple sections of pipe set on the screen as long as we have ample clearance for our tool string while bumping back. Many years ago, I developed a tool called a “screen setter downer.” This is a solid steel bar about 6 feet long with a fitting at its bottom almost the same size as the inside of the casing. At the top is a bail not much different than the bail on a bailer. Using a long hook attached to my sand line, I can lower this down on the screen after it has been pushed to the bottom with my tool string. I can then release the hook, pull my casing back and then go in with the same hook and retrieve the “setter downer” tool. This may sound a little tricky, but I have used this tool hundreds of times and it really works.
A third method of installing a screen that is not very popular in my area due to the fact that most of our wells are shallow, is a method called wash-in. It is also called bail-in or wash-down—the same terms for an identical process. In this method, the bottom of the screen is equipped with a bail-down shoe, which is the term I will use for it. This looks something like a casing shoe and it threads to the bottom of the screen. Inside, it is equipped with a short nipple that has left-hand threads. The screen with the shoe attached is lowered on smaller-diameter pipe that will go through the screen to the bottom of the casing which, in this case, would be stopped at the top of the aquifer. Using hollow rods for a screen in a 4-inch well or a bailer on a larger-diameter screen, we then drill out below the screen and it is supposed to follow the drilled hole to its final depth. If the weight of the inside drill pipe is not enough to push the screen down, we can also drive on it.
I’ve only used this method a few times and have had mixed success. I remember attempting to replace a screen in a 6-inch well through heavy gravel and, in all honesty, not getting the screen down to full depth. My father on the other hand, in the years before I joined him full time, had good success with some screens in 4-inch wells, but he admitted that these were in extra-fine formations. If you are going to attempt this method, I would highly recommend you use a factory bail-down shoe and consult with your screen manufacturer before you start if this is your first attempt at this method.
If the screen is successfully bailed down to its proper position, a weighted plug is dropped in the drill pipe and corks off the bail-down shoe as the left-hand threaded nipple the drill pipe is attached to has a little smaller ID than the drill pipe itself. The drill pipe is then turned to the right, which tightens its joints and removes it from the bail-down shoe. This is a rather complicated and time consuming method but it does work and, if the casing is super-tight, the driller may not have a choice but to use this method if a screen is required. As far as I know the drive-in method, the telescoping method and the bail-in method are the three ways to install a screen—at least the most popular ways.
Well, as you might guess I tend to get a little long-winded when talking about favorite subjects and well drilling, pumps and water supply are right near the top of that list. So, I am going to close for now and next time I will write about fittings for our well screens no matter how we install them. If you read this after you went to the NGWA Expo at Nashville, I hope you had a good time. I will not be going this year, the first time since 1975 that I have missed one of these. I also want to wish you readers a merry Christmas and a happy and prosperous 2014.