Page 299 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 275

Cementing Program [ ]
2.7.5

Slurries will have particular design requirements depending on
the objectives.
Zone abandonment. When a producing zone is exposed (either
open hole or perforated casing), cement is usually placed across the
exposed interval and a moderate squeeze is applied. Fluid loss is
matched to the formation; a high permeability zone requires a lower
fluid loss and a low permeability zone requires a high fluid loss. As
squeeze pressure is applied, filtrate will move into the near wellbore
zone. Cement wall cake will form on the face of the formation. When
perforated casing is being abandoned, cement wall cake is desired to be
built up inside the tunnels. However, if the fluid loss is too high against
a very permeable zone, cement cake nodules can build up at the casing
inside face rather than getting cake buildup inside the tunnels.
If a cement retainer is used, it can be set on wireline and the
cement stinger can be stabbed in to pump the cement. For this to work
it must be possible to easily squeeze off fluid into the zone or cement
will not reach the formation face. Otherwise, a retainer can be run on
drillpipe, cement can be pumped over the zone, pipe can be pulled
back, and the retainer can be set above the zone. Squeeze pressure is
applied and once no more slurry can be squeezed in, then the pipe can
be released from the packer leaving squeeze pressure below the retain-
er. Any cement left in the string is dumped on top of the retainer.
Spot slurry across the zone a distance above (100-300 ft) if a
cement retainer is not being used. Then pick up above TOC, circulate
out excess slurry, close the BOP, and apply squeeze pressure.
During well abandonment, cement sometimes has to be spotted
outside casings due to exposed permeable zones. The casing can be
either perforated (4 shots at 90˚ phasing) or cut, recovered, and
cemented, or can be placed across the cut off and over the exposed for-
mation. In the first case, the techniques will be as described above. In
the second case, see the next topic.
Well abandonment. Cement plugs may be set across liner laps,
across cut off casings, or placed at an intermediate depth in a casing if
a lower plug fails. The cement does not need any special properties,
just retarded or accelerated to give a reasonable setting time.
Refer to the placement techniques described for kickoff plugs,
which follows. The placement needs for a plug in casing are less
severe than an open hole plug, but some of the techniques are applic-
able and easily used.

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