Page 409 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 385

3.4.2
Casing [ ]

the seabed. In this case, the conductor can be secured and the conduc-
tor shoe drilled out with a smaller diameter bit, usually 8-10 in less
than the conductor ID. It is not necessary to drill out too far ahead of
the conductor shoe before recommencing driving since the conductor
can normally be driven deeper than the drilled hole.
Drilling out may be done even when a mudline suspension system
is not used, where penetration/shoe strength is considered to be insuf-
ficient for holding hydrostatic pressure during the surface hole section.
Offshore, especially if the flowline is a long way above sea level, a
line can be welded in to a hole cut in the conductor close to sea level
and a 6 in air-operated valve installed, aligned away from the rig. This
will be done after driving is complete. If losses are seen, the valve can
be opened so that the hydrostatic head imposed at the conductor shoe
is reduced as the returns will flow out of the valve. If the well kicks
then the 6 in valve could be closed when the diverter is closed.
After driving the conductor, it should be cleaned out with a large
diameter drill bit to the conductor shoe. If this is not done and drilling
commences with a smaller diameter bit (say 17 /2 in in a 30 in con-
1
ductor), the formation left inside the conductor can cause problems
later on. Check that the bit will clear the mudline suspension ring, if
run, and take particular care when cleaning out past the landing ring;
it can be damaged or torn off by the bit.

3.4.2. Equipment Preparation for Casing

Refer to the checklists in Appendix 4. Use these to assist in order-
ing the equipment and services, and also for checking the presence and
condition of the equipment when it reaches the rig. The following pro-
cedures are only guidelines—each job has to be planned individually.
The casing should be laid out, connections cleaned and inspected,
drifted, numbered, and measured. Subtract the make-up loss from the
total joint length; refer to the Weatherford Tubing Data Handbook or a
similar publication. For buttress threads, measure from the end of the
pin to the base of the triangle for an average make-up loss.
If it will be some time before the casing is run, make up clean dry
protectors onto the clean, dry connections. A light coating of oil can be
applied to prevent corrosion in damp conditions or where condensa-
tion is possible. Do not dope the connections.

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