Page 426 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 402

[ ] Practical Wellsite Operations
3.5.5

reduce the pump rate if significant losses occur. The cement slurry will
U-tube due to its greater density, therefore, surface active volume will
first show a gain as cement is pumped, then a loss will show until the
mud behind catches up with the cement. In a critical displacement, the
cement unit can be used to accurately displace the slurry.
Never allow the bottom plug diaphragm to be slit. This used to be
done, presumably in case the diaphragm did not rupture when the plug
bumped; but apart from being totally unnecessary, it will allow the
cement to mix with the mud ahead.
The pumps should be slowed down shortly before theoretical
bump after bumping the plug pressure up the casing to test it as per the
program. Release the pressure and check for backflow; if no backflow
then preparations can be made for the next operation. Where a solid
hanger has been used, the running tool can be laid out and the stack
nippled down; otherwise, wait on cement before removing BOPs.
If the plug is not bumped, then the casing must be pressure tested
prior to drilling out the cement.
Stinger cementing. Where the internal capacity of the casing is very
large (such as in large surface casing), a float shoe or collar with a 4 in
bore above is normally used. This allows a drillpipe stinger with a stab-
in sub to be run after placing the casing on depth and cement to be
pumped down the stinger. Lead slurry is pumped until cement returns
are seen at surface and then the tail can be pumped. This has clear
advantages: in a large surface hole that is not usually calipered and that
will be cemented to surface, cement is mixed and pumped without hav-
ing to know accurately in advance what the hole capacity is.
Offshore a ROV or wireline deployed camera may be used to mon-
itor for returns. It can be quite hard to see when the cement actually
starts returning; often a bright dye is used at the end of the spacer or
in the first part of the slurry. The dye itself can be hard to see especial-
ly in low visibility water; try adding a few handfuls of mica LCM as
well or instead; this is easy to see because it glitters when the camera
lights hit it.

3.5.5. Post-Job Evaluation

Various logs can be run to evaluate the cement job quality. Where
no problems have been seen and/or the cement job is not critical, a

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