Page 387 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 363

Drilling Problems [ ]
3.3.2

(Note: Do not position the bit below the loss zone. Any cement
remaining in the wellbore below the loss zone is a waste; if slurry
is left above the loss zone it can at least drop down and enter the
zone.)
3. Mix and pump 100-200 bbls of extended “lead” cement slurry.
4. Pump 100 bbls of extended “tail” cement slurry with 0.5 ppb
polypropylene fibers added (Dowell product D094), preferably
batch mixed in advance of the job for the best quality slurry.
5. Displace with mud. If the annulus fluid level can be estimated,
pump a quantity of mud that leaves a small quantity of cement in
the string after U- tubing. It is vital to avoid mud entering the loss
zone after displacing the cement.
6. Monitor for returns at surface while pumping and displacing
cement. If returns are seen, close the BOP and displace with mud.
Now that the annulus level is at surface, displace with the string
capacity–5 bbls instead of the originally calculated displacement.
Slow the pump if necessary so that excessive pressures are not
imposed on the well.
7. POH. Pull back two stands without filling, then fill the annulus
from the trip tank with mud to just replace the open-ended pipe
displacement. Pull back to the shoe and wait on cement samples in
the oven. It is better to add slightly too little mud than too much.
8. RIH, carefully drill out the cement. If losses are seen right away,
repeat the cement job.
9. If losses are later experienced in the same zone, repeat the process.

There are two key elements. First, placement of sufficient cement
in the zone around the wellbore so as to flood the loss channels.
Cement left in the wellbore after setting is of no benefit and may cause
an inadvertent sidetrack. Second, to ensure that the unset cement is not
displaced away from the wellbore by adding more mud than necessary
to the well as pipe is tripped out.
The first slurry should enter the loss channels easily. If the fiber
cement starts to plug the loss zone near the wellbore (indicated by
returns while displacing), this is a good sign since the plugging will
prevent migration of the lead slurry away from the wellbore.
If returns are seen at surface, the cement will have risen in the
annulus around the drillpipe. If the loss zone is still taking fluid this

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