Page 302 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 278

[ ] Well Programming
2.7.6

Fluid loss should be dictated by formation permeability. Refer to
the “Zone abandonment” previously covered in this subsection.
Slurry volume. It is important to know the actual volume of slurry
required. If a 4-arm caliper is run first, this will give accurate volumes
and a temperature survey can be done at the same time.
If the job is planned carefully, it should not be necessary to pump
large excess volumes that later have to be drilled out. Allowing 10 to
20% above open hole capacity will account for shrinkage and some
mixing at the top interface as long as mud removal is effective and the
plug is stable.
Plug stability. When slurry is placed in the open hole without opti-
mizing mud, spacer, and slurry properties, the slurry will tend to slide
down the low side of the hole (if more dense than the mud) or move
upwards due to buoyancy (if less dense). High gel strength slurry will
leave the slurry cored after pulling out the stinger. In vertical or devi-
ated holes (not horizontal) a base for the plug should be used, a high
yield/gel mud, and possibly a spacer that reacts at the mud/spacer
interface to produce a viscous or gelled fluid.
The following factors are important for first time success:

1. Reduce the difference in density between mud and cement
2. Increase the yield point and/or gel strength of the mud below the
cement
3. Use a reactive spacer above the mud as a base for the plug

2.7.6. Special Purpose Cementing

Curing total lost circulation with cement. Offset data sometimes
indicates a high risk of total losses. The following general technique
can be modified as needed and added to the drilling program.
Thixotropic cement is not needed; the technique has worked well in
practice with normal cements.

1. Drill ahead blind until it is anticipated that the loss zone has been
completely penetrated. Do not pump pills, LCM, fibers, or any-
thing similar that might impede the movement of slurry into the
loss channels around the wellbore.

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