Page 389 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 365

Drilling Problems [ ]
3.3.4

end for leaks. If both pumps show the same pressures as on the
slow circulating rates (SCRs) taken earlier, resume drilling cau-
tiously, watching for further signs of problems. If both pumps
show lower pressure, something in the circulating system must
have changed.

At this point, the surface equipment and mud have been isolated
and so the problem must be downhole. Do not slug the pipe, POH wet
to allow the washout to be seen more easily. Some old hands would
throw small rope strands down the drillstring before tripping out. The
string might be seen hanging out of the washout.

3.3.4. Backing Off

In some circumstances, when the pipe is stuck, it becomes neces-
sary to backoff the pipe at one of the downhole connections, either to
fish the remaining pipe or to sidetrack or plug and abandon.
The most common method used is to apply left-hand torque to the
string and set off a small explosive charge at the desired backoff depth.
The vibrations from the explosion cause the joint to unscrew with the
left-hand torque stored in the elastic drillstring.
Sometimes an explosive backoff cannot be done. If the string is
plugged higher up or if explosive is not available, it is possible to back-
off at or close to the desired depth. The method is less reliable than
using explosives.
Planning and precautions. A pre-job safety meeting must be held
in advance since this is a high-risk operation that the crew may be
unfamiliar with. Subjects to be addressed should include:

1. The pipe should be worked under torque and high tension with the
tongs. If the tong becomes detached or the tong line breaks, the
tong can fly across the drillfloor causing serious injury. The tongs
should be tied between the jaws when on the pipe.
2. Torque should be held in the string by the slips unless using a top
drive. If the slips were picked up with the table locked and torque in
the string, the slips can fly across the drillfloor causing serious injury.
The slips should be tied around the pipe when set in the table. No

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