Page 279 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 255

2.6.2
Casing Running Program [ ]

preventative measures can be specified by the program; well-central-
ized casing run in a well-conditioned wellbore with properly condi-
tioned mud is less likely to get differentially stuck. Careful reaming of
problem sections will only be effective for geometry-related problems.
In high-angle or horizontal wells, the casing may push cavings or
cuttings ahead and buildup a wall of debris, which may then get the
casing packed off. A casing circulating packer that will allow circulat-
ing to start with a minimum delay should be included in the program.
Consider washing every joint down from about 70˚ inclination, taking
care not to initiate lost circulation with high AVs/ECDs. A casing cir-
culating packer is cheap insurance on any casing job, but it makes no
sense not to use one for a high-angle well (>45˚), if there are any prob-
lems or if fill is anticipated.
An undergauge hole may be caused by mobile formations squeez-
ing in (e.g., salt or some shales) or thick filter cake buildup. If logs are
run before casing, a 4-arm caliper should be included in the logging
program for drilling evaluation. This gives an accurate cement volume,
and will indicate if there is an undergauge hole that needs to be reamed
out prior to running casing. In this case, a wiper trip after logging
before running casing is justified.
If filter cake buildup against a permeable sand is a problem, there
should also be concerns regarding differential sticking. One thing that
can be done is to ream down through these intervals to remove the fil-
ter cake and spot weighted, supersaturated salt pills across the sands.
This will delay filter cake buildup by several hours as the salt slowly
dissolves but meanwhile acts as a fluid loss control agent. Even if the
filter cake has started to build up by the time casing is run in, it will
not be as thick as it would be otherwise. This method can also be used
as a nondamaging temporary fluid loss/filter cake control agent for tak-
ing RFT or MDT pressures and samples, and to minimize the risk of
differentially sticking these kinds of tools.
If a build, drop, or directional motor assembly is planned, a rela-
tively stiff BHA should be used to ream through these sections prior to
running casing. When reaming a kickoff in softer formations, take pre-
cautions to ensure that a sidetrack is not drilled. Use low WOB and
higher RPM and if necessary, make a special trip with a bit-sized hole
opener and undergauge bullnose to ream out the hole.

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