Page 381 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 357

Drilling Problems [ ]
3.3.1

rather than up; if differential sticking has already started, moving down
will be more likely to get you free than pulling up, which may increase
the side force onto the sticking formation.
It is good practice on trips out and connections to set the slips on
a “down” drag. Pick up an extra 7-8 ft, come back down, and set the
slips. This does two things. It reduces the tension and stretch in the
drillstring, which reduces string side forces and sticking and also
makes it possible to cock the jar as soon as the slips are taken out. It
also confirms that you are not going to pull out of the slips straight into
a stuck point. If you see signs of the string getting tight when picking
up the extra height, go a bit further and work out the tight spot first
before setting the slips while you have plenty of height to work with.
Centralize casing well over this interval. Plan the casing job and
brief the crews well so as to avoid excessive time with the casing
stationary.
In the event of equipment failure, try to keep the casing moving
slowly while the problem is sorted out. If the casing cannot be picked
up due to weight plus drags, or to a drawworks problem, have the
driller lower the full joint very slowly, if possible, which could take sev-
eral minutes of constant slow movement.
If the weight of the casing plus drags is likely to be more than can
be picked up, consider floating in the casing (that is, running it par-
tially empty from a certain depth to reduce the hook loads). In this
case, check the collapse rating of the casing against the collapse pres-
sure that will be exerted.
Differential sticking—cure. If a likely differential sticking
zone exists in the well, it is especially important to avoid getting
stuck by another mechanism first. This requires good planning and
close supervision.
If differentially stuck, then the procedure for getting free involves
reducing or removing some of the necessary conditions. Fast reaction
is needed as the differential sticking force increases with time, so the
best chance to free the pipe occurs when initially stuck. Circulation
will be possible unless another mechanism also exists; for instance the
string may be mechanically stuck, then become differentially stuck due
to the pipe being stationary for a long time.
Start to work the pipe immediately after you become stuck. First
slack off almost all the string weight; this may cause the pipe downhole

357