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Thread: drilling a shallow well

  1. #1

    Default drilling a shallow well

    I managed to get my hands on fairly small hydraulic drilling machine, and decided to drill my shallow well. I'm down about 13 feet (the same depth I ran into trouble with my sand point attempt) and seem to once again be runnning into trouble. The drill is chattering up and down and not making much progress. There is a fairly constant stream of small river rock (1/4" - 1/2" diameter) that is being lifted out of the hole by the bentonite mixture. I'm continuing to get this river rock evne though I'm not making any progress in depth.

    I'm going to talk to the company that supplied the machine on tuesday. They have a heavy duty tri-cone bit that I can get; I'm thinking maybe this will cut through whatever is causing the trouble.

    Any hint/tips in the meantime? I'm surprised that river rock is continuing to come out of the hole even though I'm not getting depth. It must be either enlarging the hole or creating a pocket down there. The overall feeling in the way the machine is chattering is almost like there are some large rocks that are getting churned up, yet fail to lift and fall back down to the bottom. Is my bentonite not thick enough? it's the consistency of a milkshake / thin pancake batter.

  2. #2
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    If the rock is round and smooth, it's not being chewed up into smaller pieces. It's just what is down there and is saturated with water. It's like drilling into a box of marbles. Your not going anywhere. You would need to put a screen into this material and you might get some water from it. Since your using bentonite, you wouldn't know if it were taking water. Shut off the machine, break the bentonite and see if this hole will take water.

    bob...

  3. #3
    Porky Cutter,MGWC Porky's Avatar
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    Default Manufacturers aren't drillers!

    Speedbump is right. You're in a coarse loose gravel. The hole is only getting larger, not deeper. You're in an almost impossible situation with these portable drills. I teach drilling with these portable drills internationally. They are great but do have their limitations. Your situation is just one of them.

    If you call the manufacturer tell them you have been communicating with "Porky".

    Forget the roller cone rock bit. It will only compound your problems.

    EXAMPLE: Have you ever dug a hole in the sand on the beach? When you hit water the hole won't get deeper, it only gets bigger! You're existing hole will only continue to get bigger. . . you must move!

    You have two possible options:
    1. Try driving a 1 foot drive point into the gravel as far as possible, then backwash the bentonite from inside the drop pipe to the surface until reasonably clear. Then connect a pump to see what the well point will supply.
    2. Abandon the existing hole and move the drill at least 10 feet; mis up some heavy bentonite (looking about the consitency of a thick milk shake); Drill the new hole slowly. Keep the bentonite thick. Have your casing and well screen/point ready and when you get to a preferred depth; remove the drill stem and bit quickly as possible and immediately install the casing and point. NOTE: Due to this hole problem I don't recommend using over a 2 ft. screen and at maximum 3 ft.
    Once it's installed to the bottom, connect a pump and pump until clear. If it pumps satisfactorly, pour 3 gallons of clean coarse sand around the casing then add clay or bentonite to the top. Most states require the top 20 ft. being bentonite grouted with hole plug. Look up www.dci-inc.us

  4. #4

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    Quote Originally Posted by speedbump View Post
    If the rock is round and smooth
    I inspected the cuttings, and the rock that's coming up is round and smooth on one side, but cleaved/sheared on the other side(s). It looks kinda like river rock that's been through a crusher. This leads me to think (please let me know if I'm wrong) that the machine is encountering larger rocks and busting them up.

    It's not easy to try to get an idea of the size of the parent rock before it was broken up, but my best guestimate is that the rocks may have been 1" to 3" in diameter before being crushed.

    The bentonite mix that I'm using is very thick; about as thick as the mud pump will reliably work it.

    My plan is to resume drilling this weekend, see if I can make any depth. If I'm not making depth, I'll try pounding a sand point in as suggested and see if I get any result. This seems to be the same depth that the last sand point refused to go through, so I'm not hopeful that pounding a sandpoint into it will be successful.

    Porky -- I'm curious why you recommend backfilling around the sandpoint with sand (assuming I go that route) ... I had thought about this alternative earlier (installing a sandpoint in the hole rather than reaming it out and putting in a casing), and I had assumed I would just backfill around the point with small gravel. Is sand a better material to use?

    Assuming I end up at a final depth of < 25 feet, is there any advantage to going the (4") casing route rather than just sticking a sand point in the hole?

    Thanks

  5. #5
    Previous member sammyhydro11's Avatar
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    Drilling with a betonite mix to install a point well will plug up the formation that you are trying to pull water from.You will have a real hard tim trying to break up that mixture to allow that water to flow into your screen. By augering you get a good visiual of the material that you want the well screen in. How deep is it to water in this hole that you are drilling?

    sammy

  6. #6

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    Quote Originally Posted by sammyhydro11 View Post
    Drilling with a betonite mix to install a point well will plug up the formation that you are trying to pull water from.You will have a real hard tim trying to break up that mixture to allow that water to flow into your screen. By augering you get a good visiual of the material that you want the well screen in. How deep is it to water in this hole that you are drilling?
    The depth to water in the hole appears to be approximately 3 feet. The hole is currently about 13 feet deep. Thus there's about 10 feet of water in the well.

    As per suggestions, I tried to clear the well of the bentonite and dropped a sandpoint down. I then connected my trash pump to the sand point and pumped it at maximum rate. It took a few iterations of pumping/backflushing to get it so the sand point would not get immediately plugged. Once drained, water slowly fills back into the well. I can run the trash pump maybe 20-30 seconds, at which point it runs dry, and then have to wait a couple minutes for water to flow back in, and then I can run it for another 20-30 seconds. I haven't computed the GPM of doing this (it got dark), but at the current rate it's not enough GPM to do anything useful with.

    The sand point is currently resting on 12-18" of loose gravel. This is the same material that the drill was having trouble with -- I'd drill through it, the machine would lock up, I'd back out, and have to drill back through it again (i.e. with the drilling machine, I'm drilling through the same 12-18" of material over and over again). It might be possible to pound the sand point further into this material; it has to be pretty well ground up from running the drill through it multiple times. I might give that a shot tomorrow.

    Personally I think the mud pump they supplied me with is too small for the task. I'm not sure if it has enough flow to lift the larger gravel out of the well. Either that or new gravel is continually caving back in -- I *thought* a good thick bentonite mix was supposed to take care of that. Of course the thicker I make the bentonite, the more difficulty in pumping it.

    Can anyone tell me -- can you buy just the "pump" part of a mud pump? I have a decent 18hp gas engine laying around, and I'm handy enough to fabricate the rest of the parts if I could get a quality pump head. I'm thinking an 18hp pump might do what the 5.5hp pump I'm using now cannot. This would probably be a project for the fall, as I also need to beef up the machine's water swivel.

  7. #7
    Previous member sammyhydro11's Avatar
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    I say you are wasting your time drilling a point well with a betonite fluid. That fluid fills the pour spaces that the water needs to travel through to get into the well.

    You need to call a drilling company that has hollow stem augers to complete your well. The hollow stem augers will allow them to drill beyond the gravel without having to use a drilling fluid. Once they get to the depth where the screen needs to be, they can easily place it in the hole because of the hollowed out space in the augers.

    sammy

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