ream down to this mark over a 15 ft to 30 ft (5 m to 10 m) interval. The reaming ROP should be
5% to 10% of the drilled ROP in the parent wellbore, and RPM should be drilling RPM or 120
rpm to 150 rpm.
• It is important not to ream beyond the sidetrack depth or the ledge will be destroyed. The time
taken to initiate this ledge will depend on the formation drillability and hole inclination. As a rule
of thumb, ream downwards to the sidetrack point up to 10 times at 5% to 10% of the drilled ROP.
Indications of the ledge being created will be a small increase in WOB or change in continuous
inclination.
• Commence controlled drilling at 10% to 15% of the drilled ROP monitoring WOB and continuous
inclination to avoid creating excessive doglegs.
• As the sidetrack progresses the Bias Unit steering pads will not be in contact the high side of
the hole. The side cutting action of the bit, high RPM and the side force created by gravity are
the primary sidetracking mechanisms.
• After the sidetrack has been initiated, closely monitor the inclination from the tool to avoid
excessive doglegs.
• With an open hole sidetrack, it is particularly important to carefully ream the sidetrack transition
to make sure that it is clear from debris and as smooth as possible.
• After the sidetrack has been initiated, and preferably before making a connection, reduce the
RPM to between 40 rpm and 60 rpm, and slowly backream through the transition. Shock and
Vibration levels should be monitored as well as indications of overpull or packing off. Reduce
the pump rate and RPM then run back through the transition at approximately twice the normal
drilling rate. Repeat this procedure twice more. Stop if there is any sign of hanging up.
• If the BHA hangs up, increase the flow rate and set the PowerDrive toolface to lowside (or the
sidetrack direction). Run back through the sidetrack transition. Use of real-time inclination will
confirm entry into the sidetrack wellbore.
• On subsequent trips though the sidetrack transition, care should be taken to avoid damage to
the transition and entering the original hole. Use of real-time inclination from the PowerDrive tool
is beneficial in confirming entry into the sidetrack.
Casing exits and whipstocks
All PowerDrive tools can be used to sidetrack off a whipstock. However, it is not recommended to drill
directly off the whipstock unless there is a suitable length of rat hole. This will help to ensure that the
PowerDrive is not damaged by rotation over the whipstock or window.
Experience has shown that significant tool damage occurs if the PowerDrive tools are rotated in contact
with the whipstock body. The following procedure is recommended:
• Ensure a sufficient length of rat hole is drilled with the mill assembly, 9 ft to 15 ft (3 m to 5 m)
minimum is recommended.
• To avoid the possibility of the milling assembly damaging the anchor slips an extension should
be added between the whip face and the anchor slips.
• Window milling and kicking off from a whipstock is a specialized operation and the service
provider should be consulted prior to the job. There is always a risk of the milling assembly
tracking the casing and failing to kick off in the following circumstances:
o The milling assembly is too flexible
o The length of rat hole is too long, and separation from the original hole has already been
lost.
o The length of rat hole is shorter than absolutely necessary to allow the PowerDrive
stabilizers to clear the window
o The mills are unable to cut laterally in hard formations as the window is exited
o Poor quality cement
o Milling multiple casing strings.
• Make sure mills are in gauge after window milling (make sure they have been correctly gauged).
• Initially run through the window without rotation or flow. Do not rotate the tool through the window
to minimize bit and pad damage when running in/out of hole.
• If resistance is encountered, the PowerDrive toolface can be oriented to the whipstock direction
and the tool rotated slowly with a reduced flow rate. Do not rotate more than 25 rpm to avoid
damage to the tools.
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