Percussion Jet Drilling

Percussion Jet Drilling

This writer has drilled over 6,000 wells by the percussion-jet drilling method. It is fast and efficient and possibly the cheapest drilling method available for depths up to 200 feet or more in unconsolidated soils and even some rock.

Along with the usual equipment needed such as a derrick or well machine, block and tackle or power source, pressure pump, drive hammer, casing and other, associated tools and material, a drill is needed. The drill is attached to the bottom of the drill pipe. This drill may be any of a number of designs, from flat chisels with jet holes on each side, to star drills with four jet holes. They might be "S" drills, or "stepped drills" which are longer at the center or longer on the outer cutting edges - but all with the necessary jet holes to allow water pressure to clear the drill and at the same time, force the cuttings up and out of the casing.

The equipment is set up as before including a 30 inch settlement trench. Dig a three foot deep starter hole. Raise the first section of drill pipe with the drill attached. Start the pump circulating the drilling water through the drill. Attach a turning clamp onto the drill pipe and start the percussion-drilling procedure. The drill is raised about two feet high and then dropped - repeatedly. A good operator will get 50 to 60 drops per minute. While the drilling is being done, the force pump is circulating water through the jet holes in the drill which wash out the cuttings and force them to the surface where they settle in the trench.

While doing this, the driller turns the pipe about an 1/8 of a turn per drop until he makes more than one-half a turn; then he turns the pipe 1/8 turn per drop in the other direction, repeating this over and over again until the hole is deeper than the first length of casing to be installed.

The drill is then removed from the hole and the first length of casing is attached and lowered into the hole opening. The casing is raised and dropped, as was the drill pipe, to place it into the drilled hole. The drive hammer is then inserted into the casing top and dropped onto it, repeatedly, until the casing is driven into the hole. A pipe wrench with extension is used to turn the casing, slightly, at each drop.

The driving is continued until the casing is just above ground level. The drill pipe is then attached once again and drilled through the first length of casing. When this point is reached, the drill pipe is clamped off on the installed casing and another length of drill pipe is added. Again, drill the length of this second pipe and remove drill pipe. Add another length of casing and drive it to ground level. Repeat drilling inside the casing, and driving more casing, until a solid formation or rock is reached. Set the casing firmly into the rock. Usually, no more casing is required.

Assemble the drill pipe in the casing and continue drilling until a water sand formation or porous water stratum is reached. The driller must watch and check his drilling mud many times to locate the water stratum. When this is reached, the well will usually start to lose water. The driller may want to drill deep enough into the stratum or through the stratum, if possible, to obtain the quantity of water desired. After removing the drill pipe, the well is developed until clear and free of sand.