The next technique for drilling in sand involves using bentonite to hold the hole open. As we have already seen, sand will quickly collapse on your drillpipe when drilling in sand. When the drilling fluid contains dissolved bentonite it creates a coating on the inside of the hole that keeps the sand from collapsing, thereby holding the hole open.
It is absolutely critical that the bentonite be thoroughly mixed with water before using. If you haven’t already done it, please review the page “Drilling Deeper with BENTONITE” before going further
You can either use the modified drill head shown below for adding bentonite or use the mud pump system.
Drillhead with valve on top for adding bentonite
Keep in mind that while bentonite helps while you are drilling, it hurts when you start to pump the well. The bentonite cake or coating keeps water away from the inside of the hole and the well screen. So, it helps you while you are drilling. It works against you when you start to pump the well because it keeps water out of the hole. So, the trick is to use it while drilling but when you get to the depth where you are going to be setting your screen, stop using it so that bottom layer will let water through.
As information – later when you start pumping the well, it is common for well production to start slowly and improve as the flow of fresh water into the hole weakens the bentonite coating.
My suggestion for the drillers using two hoses as drilling fluid is to use plenty of bentonite as you are drilling and then quit just before you get to depth.
For example, say you have a 10 foot standing water level and your plan is to dig a 30 foot hole and put a four foot well screen at the bottom. Use a two inch drillpipe. Use plenty of bentonite for the first 25 feet. Then for the last five feet don’t use any bentonite. Just drill with pure water. Even with the sand collapsing you will be able to drill five additional feet with no bentonite.
Then, while the water is still running make up your well screen piece. Attach your four foot long 1.25 inch diameter well screen to about 27 feet of 1.25 inch PVC. This will give you a 31 foot long well screen piece. Perfect for your 30 foot hole.
Make sure you have some help for this next step.
Next, turn off the water supply from the two hoses. Then, quickly:
- 1. Remove the drill head from the two inch drill pipe.
- 2. Put the 1.25 inch well screen pipe down through the two inch drillpipe.
- 3. Once the well screen pipe is in place, pull the two inch drillpipe up and out of the ground. Be sure and pull it straight up for the first ten feet so the well screen pipe will not be pulled up with it. After that, the sand should collapse on the bottom of the well screen pipe and hold it in place while you remove the two inch pipe.
Pull the two inch drill pipe completely out of the ground. You can re-use it on the next well you drill. The remaining 1.25 inch PVC well screen piece is your well. Hopefully about a foot of it will be sticking out of the ground. Attach a pump and start pumping the well.
If you can arrange it, it is best to attach a trash pump or a temporary pump when you first pump the well. New wells typically produce sandy water and the sand will eat up the plastic impeller in a pump. If you can pump out the sandy water with a sacrificial pump or a mud pump, then your permanent pump will both last longer and work better.
OK, so you were happily drilling away and you were almost there and maybe you took a break, or the phone rang, or whatever and the pipe stuck. You’ve got a nice deep hole with a stuck pipe. You know you are in water because several days later water is still standing in that two inch pipe.
Wait! Stop! Don’t jump! Crawl back in off the ledge of the basement window. You can still use that hole.
If you want to get the pipe out of the hole, please check out the page, When the Pipe Sticks.
If you want to use the pipe as it is, There are two techniques:
1st stuck pipe technique: Attach your water supply to a 1.25 inch pipe. You can usually adapt your two inch drillhead to the smaller pipe. Use the 1.25 inch drillpipe inside the stuck two inch drillpipe to drill the hole way past the bottom of the stuck pipe. Use a little bentonite. While you are doing this, it is usually a good idea to attach a two inch Tee to the top of your stuck two inch pipe so the cuttings will be directed to the side.
Once you get to the depth you want to set your well screen, keep the water water running while you make up your wellscreen pipe. I know this is wasteful of 1.25 inch PVC but there is no way around it. Make up a 1.25 inch well screen pipe with a three or four foot long piece of 1.25 inch diameter well screen at the bottom and 1.25 inch diameter PVC above that.
Then similar to the protocol described above:
Turn off the water supply from the two hoses. Then, really quickly:
- 1. Remove the drill head from the 1.25 inch drill pipe.
- 2. Pull the 1.25 inch drill pipe out of the stuck two inch drillpipe ground and put the the 1.25 inch well screen pipe back down down through the two inch drillpipe.
The idea is to take the drill pipe out of the hole and then put the well screen pipe back down before the sand collapses. It is likely you won’t get quite as much back down as you took out.
Sealing the well – After you finish and have your well producing like you want it, you’ll need to fill that two inch pipe with bentonite or cement to keep groundwater out of your well.
2nd stuck pipe technique: Simply use your stuck two inch pipe as a head start for a drive point!