Page 304 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 280

[ ] Well Programming
2.7.7

(indicated by returns while displacing) because the plugging will pre-
vent migration of the lead slurry away from the wellbore.
If returns are seen at surface, then cement will have risen in the
annulus around the drillpipe. If the loss zone is still taking fluid then
this should drop when pumping ceases to the level supported by the
formation fluid pressure and the cement that has moved up the annu-
lus will probably drop down back to the loss zone.
Repairing damaged casing. The technique will be similar to spot-
ting and hesitation-squeezing cement over perforations (see “Zone
abandonment” in Section 2.7.5), usually without a cement retainer.
Use slurry with low fluid loss and high strength so that cement pene-
trates through the split and forms a high-strength sheath in the annu-
lus. Thixotropic slurry may be used so that it will not move away from
the area of the split after spotting.

2.7.7. References for Cementing Program—Design

Nelson, Erik B. Well Cementing, published by Schlumberger
Educational Services (order number SMP-7031).

“Process Implementation Improves Cement Plug Success,” from
Cementing the Future Petroleum Engineer International, Hart
Publications, 1996. Supplement.

280