Page 374 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 350

[ ] Practical Wellsite Operations
3.3.1

work out. If you have problems picking up to make a connection in
these shales, sometimes you will find that after a period of time the
shales cave slightly into the wellbore and the problem cures itself while
you are drilling. Field experience will dictate whether this is the case.
You can experiment (in a development area) if previous wells have
had problems picking up to make connections by only working/back-
reaming enough to make the connection. Drill ahead and when you
come to POH, trip carefully through the troublesome intervals and note
how much you have to work to get through. This may save time on
future wells.
Keyseating. Pipe stuck in a keyseat will only occur when pulling
out of the hole. The top drill collar or stabilizer will be the most likely
item to hang up in the keyseat.
If the deviation profile and formation type make a keyseat likely,
consider running a keyseat wiper on top of the drill collars or prefer-
ably, if one is available, run a string reamer in the drillpipe (refer to
“Keyseating” in Section 3.7.2).
If stuck in a keyseat, the jar will not work if the stuck point is at
the top of the drill collars (above the jar). In this case, work the string
in compression, letting it drop and catching it sharply with the brake to
send a shock wave down the string. If one is available, a surface jar does
the same thing only more efficiently. However, if the stuck point is
deeper than about 700 m (or less if the well is crooked or significantly
deviated above this), then the shock wave will probably not be great
enough at the stuck point to have much effect.
If the downhole jar is working, the prognosis is much better. Limit
the overpull at surface to just enough to cock the jar (if it jars down-
wards) and work/jar down. Do not allow the jar to fire upwards, since
this will force the BHA tighter into the stuck point.
Be prepared to backoff above the drill collars and run a fishing
assembly consisting of overshot - fishing bumper sub - 2 drill collars -
fishing jar - 3 drill collars - accelerator. A sub with the correct pin to
make up into the fish plus a safety joint could also be run instead of an
overshot. Bump/jar down to free.
Stiff assembly. Where a stiff BHA is to follow a more flexible one,
or where a rotary assembly is run after pulling a motor, lay out
enough drillpipe to ream the complete section drilled with the more
flexible assembly.

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