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Cable tool rigs
are a traditional way of drilling water wells
internationally and in the United States. The majority
of large diameter water supply wells, especially deep
wells completed in bedrock aquifers, were completed
using this drilling method. Although this drilling
method has largely been supplanted in recent years by
other, faster drilling techniques, it is still the most
practicable drilling method for large diameter, deep
bedrock wells, and in widespread use for small rural
water supply wells.
Also sometimes called "spudders", these rigs raise and
drop a drill string to finely pulverize the subsurface
materials. The drill string is comprised of the upper
drill rods, a set of "jars" (inter-locking "sliders"
that help transmit additional energy to the drill bit
and assist in removing the bit if it is stuck) and a
drill bit. During the drilling process, the drill string
is periodically removed from the borehole and a bailer
is lowered to collect the drill cuttings (rock
fragments, soil, etc.). The bailer is a bucket-like tool
with a trapdoor in the base. If the borehole is dry,
water is added so that the drill cuttings will flow into
the bailer. When lifted, the bailer closes and the
cuttings are then raised and removed. Since the drill
string must be raised and lowered to advance the boring,
casing (larger diameter outer piping) is typically used
to hold back upper soil materials and stabilize the
borehole.
Cable tool rigs are simpler and cheaper than similarly
sized rotary rigs, although loud and very slow to
operate. The world record Cable Tool Well was drilled in
New York to a depth of almost 12,000 feet. The common
Bucyrus Erie 22 can drill down to about 1,100 feet.
Since cable tool drilling does not use air to eject the
drilling chips like a rotary, instead using a cable
strung bailer, technically there is no limitation on
depth..
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