Page 38 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:55 PM Page 14

[ ] Well Design
1.1.2

ties. Logging will show large washouts (off-scale in places), but the
benefits in saved time with avoided losses more than compensates.
If losses occur in spite of good mud control, try reducing the cir-
culation rate. You may find that a small reduction is all that is needed
to cure the losses. After an hour or two of drilling ahead, it may be
possible to slowly bring the circulation back to full rate. If total loss-
es occur, first measure how much water is needed to fill the annulus.
If the hole is static and full with water on top, slowly kick in the
pumps and try to attain a circulation rate that will at least lift cuttings
up the hole to the loss zone and cool the bit with very low weight on
bit/revolutions per minute (WOB/RPM). Circulation of 250 gallons
per minute (GPM) will give 50 feet per minute annular velocity (FPM
AV) around 5 in drillpipe in 12 /4 in hole; this should be used as the
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minimum. Drill ahead at reduced parameters and monitor drags and
torques carefully for signs of drilled solids causing problems (poten-
tial stuck pipe). The losses are likely to cure themselves as generated
cuttings act as lost circulation material (LCM) to plug the loss zone.
Note that in past wells, LCM and cement have both been pumped, lost
lots of time, and did not work.
The shale interbeds need a fair amount of inhibition and by expe-
rience it has been determined that if KCl is maintained at 40-42 ppb
and shaledrill polymer at 1.0-1.5 ppb, there are no shale hydration
problems. Keep a close eye on the mud properties and have the mud
man run several tests throughout the day. The drilling engineer can be
delegated the specific task of keeping an eye on this and personally
supervising the tests to ensure that the tests are done properly and
accurate results are given. There have been cases of mud men giving
false results after a test to make it look as if the mud is in good shape
when in fact it needs treatment.
In order to get the best drilling performance, the driller has to have
the freedom to adjust the parameters for best ROP. The formation is
quite streaky and changes constantly. The limestone is more sensitive
to high RPM/lower WOB and the shales are better drilled with maxi-
mum WOB/lower RPM. If the driller is given a range of parameters to
work within and is constantly experimenting for best ROP, the overall
bit run will be far better.

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