depending upon how tightly and in what manner the drill
pipe is stuck.
When the drill pipe becomes stuck by balling up
while drilling in soft shale or clay, it can often be
loosened by circulating clear water. An upward strain
should be kept on the pipe while circulating the water.
When the pipe is stuck by sand or drill cuttings that
have accumulated in the hole, circulation should be
maintained with the heaviest mud obtainable. When
possible, the pipe should be worked. Any movement
transmitted through the pipe, however slight, helps
dislodge the sand particles into the mud stream that
carries them to the surface.
When a drill pipe is stuck through lack of
circulation, there is not much that can be done to recover
the entire string of pipe; however, an attempt should be
made to pull the pipe with jacks. Sometimes the pipe can
be recovered by mixing the proper circulating fluid and
circulating it while working the pipe with both the
rotating and hoisting mechanisms. In some instances,
the pipe can also be recovered by cutting it with a
blasting charge in the bottom of the hole or about where
the pipe is stuck.
Fishing
One of the major problems encountered when well
drilling is the recovery of tools lost in the well. Lost tools
are recovered by fishing. The most frequent cause of
tool loss in rotary drilling results from the drill pipe
twisting off. Such “twist offs” usually occur near the
lower end of the pipe. They may consist of a simple
shearing off from the pipe or of a fracture at a coupling.
The accidental dropping of a drill pipe into a hole also
calls for fishing. Among less common accidents
requiring fishing is the dropping of tools, such as slips
or wrenches, into the hole. When a break occurs,
remember the exact depth of the break. This helps in
locating the tops of the tools and coupling to them with
a fishing tool. Recovery of lost drill pipes depends upon
whether the driller can set the tool down on top of the
pipes and connect to them.
Some of the more common fishing tools are the
circulating-slip overshot, the die overshot, and the
tapered fishing tap (fig. 9-13).
The circulating-slip overshot, as implied by its
name, provides circulation through the lost pipe to assist
removal when fishing. This tool is similar to the die
overshot in its action but provides a watertight coupling
between the drill pipes.
Figure 9-13.-Tap and overshot fishing tools.
The die overshot is a long-tapered die of
heat-treated steel. When fitted over the lost drill pipe and
rotated, the die overshot, like the fishing tap, also cuts
its own threads. The tapered thread is fluted to permit
the escape of metal cut by the threads. The upper end of
the die has a thread to fit the drill pipe. The die is hollow
but, as is also true of the tap die, circulation cannot be
completed to the bottom of the hole through the lost
pipes because the flutes allow the fluid to escape.
The tapered fishing tap, as its name implies, is a
fluted tapered tap made of a heat-treated steel. Its action
is similar to that of a machine tap, as it cuts its own
threads when rotated, and thus grips the lost drill
pipe.
REMEMBER: In many shallow wells, it is more
economical to abandon the hole than it is to fish for the
lost tools.
WELL DEVELOPMENT AND
COMPLETION
Once an aquifer has been tapped by the drilled hole,
the important and essential phase of completion and
development must be accomplished in order to assure
maximum yield under sanitary conditions.
Development and completion of a well includes
1.
2.
3.
setting the casing and screens,
removal of the drilling fluid, and
stabilization of the aquifer by removal of a
predetermined percentage of the fines, grouting,
and sterilization of the well.
9-15
