Page 379 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 355

Drilling Problems [ ]
3.3.1

If the formation is particularly bad, it may be better to attempt
to drill through it, then case it off as soon as possible, even if this
means having to run an extra casing string. It may also be possible to
set cement across the formation and drill out through it to stabilize
the formation.
Junk. Ensure all drillstring components are inspected before the
well in accordance with API Recommended Practice RP7G and that
good handling and running practices are used. Use the correct size and
grade of drillpipe. Keep a good check on the condition of slips, slip
dies, rotary bushings, tong line pull sensators, and elevators. These will
help avoid downhole failures leading to junk in the hole. Ensure that
the crew follows good procedures to avoid junk falling through the
table and that rams are closed when out of the hole.
If stuck on junk it is important to try to determine what the junk
is, where it may be positioned, and how it is sticking the string. How
to get free will depend on the situation.
Cement blocks. Where a large pocket exists under a casing shoe,
cement in the pocket after cementing the casing may fracture as
drilling progresses and fall into the hole. Do not program in a pock-
et under the casing to be any larger than necessary. It may help to
add polypropylene fibers to the tail slurry when cementing (e.g.,
Dowell product D094). In the case of pipe sticking due to cement
blocks, the method of recovery is detailed in Section 3.3.1,
“Fractured and faulted formations.”
Soft cement. It is possible to run into cement that is not com-
pletely set, then find it impossible to pull back out or to circulate.
Monitor surface cement samples (preferably kept at bottom hole circu-
lating temperature) to ensure they are hard before approaching bottom
and run in the last couple of singles slowly and with the pumps on.
If stuck in soft cement try to jar free while maintaining pressure on
the standpipe. If unable to wash/jar free, a backoff will be called for, fol-
lowed by a washover fishing string, sidetrack, or abandonment.
Differential sticking—avoidance. As was noted in Section 2, there
are four conditions that must all be present for differential sticking to
occur. Avoidance and cure focuses on reducing or eliminating these
four conditions.
A permeable zone covered with wall cake is one of the four condi-
tions. Where such a zone is identified, the wall cake characteristics can

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