Circulating excess cement off the top of a liner hanger
system can be one of the trickier parts of liner hanger installation and
several things need to be considered. I shall not try to address them all but
provide this as food for thought and perhaps it will stimulate discussion.
First and foremost, consider carefully your cementing volume and the amount of
cement that could be above the top of the liner, in length terms and volume,
also how you will handle it at surface.
Do your cement calcs :
- Consider what if
any excess you will pump and what the impact of this will be - if you don´t lose
any cement what the height of the plug above the liner will be with the
deployment drill pipe in.
- Consider the ECD pressure that this volume will be
once it is all in the drill pipe with any weighted spacer that was ahead of it,
this pressure can sometimes be quite a surprise.
- Consider what pump rate you
can achieve with this ECD and still handle it at surface when the cement
- Consider the time it will take, including picking up the running
tools, getting them to the top of the liner, closing the BOP´s etc, lining up,
making sure the cement head can go this high with the hoses etc, all as part of
your slurry thickening schedule, add it to the placement time and make sure you
allow a safe total job time from start to finish.
If you are using an integral
liner top packer you are probably using a retrieve-able pack-off and tail-pipe
for the liner wiper plug/s :
- Make sure you can pull this all the way up, they
are often telescopic and take more distance to get to the liner top than you
think. Normally the integral liner top packer is set with the packer setting
tool before the pack-off is pulled, which avoids u-tubing.
reversing out the cement, based on your prior shoe and its leak-off and the ECD
calculated for reversing out, if you do not see any clear indication of the
packer setting, as you could squeeze the cement down the liner top whilst
One thing to consider is pulling the pack-off, but leaving the
tail-pipe inside the liner top, then pumping +/-25bbls the long way to move the
cement above the liner top by say 200ft or so, then pulling the tailpipe above
the liner top before you start reversing. This serves several purposes :
proves the slurry is move-able, you might get an indication of the volume above
the liner top due to the differential pressure to move it slowly
- It also helps
to avoid cement being reversed into the liner top which later can confuse when
you enter it with the clean-up string.
I would only reverse out cement if you
bump the plug and it holds pressure and you check your floats and they are
Also have a contingency to pull above the planned top of
cement and circulate out the long way, being sure you can handle any cement
that does come back, if it does. Be sure to jet and flush the area below and
through the BOP´s when you get out of the hole.
I would have a thorough
rig-site pre-planning meeting to agree all of the above and be sure the
decision sequence is agreed between all parties before you start the job. My
experience having run many liners (in a former life) is that focus and attention
lapses once the liner is at TD, the hanger is set and the cement job finishes; and as those experienced know the liner hanger job is possibly entering its
most critical phases, getting the running tools out, not dragging the liner up
the hole, getting the packer set and dealing with excess cement.
I also advise
checking the running tools carefully when they are out of the hole as often
indications of success or failure are observed from shear screw remnants,
pack-off seals, dogs on packer setting tools etc, cement residue and the like.
Finally when you are well above the liner, after circulating out the cement, prior to pulling out anymore consider pumping
down a solid rubber flexible ball to clean the ID of the drill pipe.
above helps your planning considerations.