Overflow Drilling 1

[stephane]

We have a problem of leakage for two holes, how to stop the water outflowing?

After 10 meters of weak peat we met the clay layer that contains an important aquifer located down to it. The clay layer did burst while drilling and let the waterflow outgoing from casing with 8 cum/h discharge and 1 bar pressure at floor level and leaking in surrounding soil.

Nowadays water is still running as it was not possible to grout the hole in spite of pumping water. Because of running water that get the grout out and sprays it in surrounding soil. No grouting pressure can be used due to peat.

If anyone faced similar case or has got any idea to solve the problem, please let me know.

 

[georam]

The first thing that you must find out is how high is the water level above the ground. If you put a piezometer pipe and seal the ground surface around the pipe (temporarily), how high the water shoot up in the piezometer tube? This shows the pressure exerted upwards. You see flowing water even if the piezometric level is just a few inches above the ground. If that would be the case, you may be able to seal the hole easily.

Could you seal the hole by pouring in bentonite grout mix ? The mix can be made as a thick grout, or mixed with sand and cement so that it will be heavier than water (tends to go down the hole, rather than floats). You may have to inject the grout at depths (by using a grout pump into the hole), hence replacing the column of water above it, and creating a column of heavier liquid than water (therefore can stay and not expelled out of the hole).

Bentonite is critical in the mixture, as it swells or expands, and therefore will inhibit water flow. It may need time, and waste of the bentonite-cement mix, but the flow will slow down as the bentonite swells.

If flow is small, you may just use bentonite pellets and drop them in the hole. The pellets come in different sizes, from pea size, marble size to powder. You can even mix bentonite powder with water and make your own "bentonite balls" to the required size (1 to 2 in. diameter), and drop them one by one into the hole. Bentonite alone is heavier than water, so it may go down. You have to do it slowly to ensure that the hole is not plugged too quickly. To ensure a long term seal, you have to create a good column of bentonite seal, say at least 30 cm, and then backfill the remaining hole with cement grout or soil).

Hope that this helps

 

[bmike]

If possible, extend the casing above ground to a sufficient height that it exceeds the piezometric head at the bottom of the casing. The flow will eventually stop as there will be no hydraulic gradient. It is then a relatively simple matter to install a grout or bentonite seal.

If this height is too excessive, try putting an inflatable borehole packer into the caly layer. Use one that allows you to pump grout through it. Seal the hole below the packer and get your packer back, if possible.

 

[mudman]

I have had this problem in the past and the use of bentonite is the key. The problem is how to place the seal. What has worked for me in the past, depending on the size of casing is to use bentonite plugs. Pellets and tablets will probably get washed out, the same applies to bentonite grouts. The simplest solution generally works. We used on one occasion, whole bags of bentonite dropped down the hole. If this fails, due to casing size, use stockings or hessian bags (filled with bentonite) dropped straight in.

 

[doc11]

I had similar problems while drilling in Utah last year. We were able to control the formation using weighted drilling muds (up to 12 lbs per gallon). We grouted the borings using cement with barite added to bring the weight up. We didn't weigh the grout but the mix is:
25 gal water
3 bags portland cement
3 to 4 100 lb bags of barite
The mix will be very heavy and a temporary casing should be set to the bottom of the peat.
A high volume will have to be pumped at first to overcome the water flow. Afterward the grout will have to be watched for settlement and kept topped off.

 

[hogwart]

Stephane, Did you get an answer to your problem of the flowing well or is the well still flowing?

 

[TJWATKINSPG]

Barite is an excellent source of material to add wieght to the bentonite mud column. The real trick is to get the piezometric head to exactly equal the pore pressure at the aquifer. Good luck, it might take a few attempts but the balace is possible. The truth will set you free. Best of luck. Geodude