Page 119 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 95

1.4.21
Casing Design [ ]

These integral packers are quite reliable and can be routinely used.

Liners may also be set on bottom and cemented without hanging off
on the previous casing, though this is uncommon. A cementing shoe
with side passages is needed instead of the more conventional type.
Hangers (surface wellhead). The choice of hangers will be limited
to those compatible with the wellhead system. On a nonfloating rig, a
solid (mandrel) hanger may be used to allow the BOP to be safely nip-
pled down without having to wait on cement, if other circumstances
allow. Setting these hangers is simpler and safer than lifting the stack
and setting a slip and seal assembly, trimming the casing, and running
a seal bushing for the next spool. More care is needed to space out, and
a landing joint of appropriate length to reach from the top of the hang-
er to the drillfloor is necessary.
If a solid hanger is to be run, a slip and seal backup will still be
needed to land the casing if, for some reason, the casing is not run all
the way to planned depth. Therefore, a slip and seal assembly and a seal
bushing should be kept handy for emergency landing. A solid hanger
cannot be used to land the casing under extra tension, which is some-
times done to prevent buckling.
Other accessories. If casing is to be reciprocated while cementing,
scratchers may help remove wall cake and induce turbulence.
External casing packers (ECPs) are designed to seal off the annu-
lus to stop gas or fluid migration through the setting cement. The dan-
ger here is that below the ECP, hydrostatic pressure will drop very
rapidly as the cement sets unless special additives are used, so that the
cement below the ECP could become porous due to gas flow from the
formation into the setting cement. Consult the cement contractor and
consider all the factors carefully before choosing to use an ECP.
Special cement heads are available to allow you to rotate the cas-
ing during displacement. However, experience shows that reciproca-
tion during displacement is more effective in displacing mud.
Reciprocation must be used with caution in sticky hole conditions,
especially if using a fixed hanger that may be in the BOP if the casing
gets stuck while reciprocating.

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