4.3 Shock & Vibration
Too much shock and vibration can be destructive to all BHA components and needs to be actively
managed to avoid costly tool damage or, in extreme cases, parts left in hole. All well planning must
include a plan to deal with high shocks and stick-slip. If experience from offset wells shows that high
shocks and vibration are likely to be a problem, consult the client at an early stage. Create a clear action
plan before the job begins, with agreement on the actions to be taken if shocks become excessive. There
will be some occasions where excessive shocks can never be completely eliminated, and the best option
may be to trip out of hole. Extreme shocks can damage all BHA components including MWD/LWD tools,
bits, stabilizers, collars and BHA rotary shouldered connections. Shocks off bottom are of equal
importance and must be managed in the same way as drilling shocks. Shock and vibration management
should be promoted as good drilling practice, as well to make sure that the tool operates in the most
favorable environment.
Active management of shocks and vibration requires that the problem be recognized, and then
the appropriate action taken.
Low level shocks over a long period of time can be as dangerous to the tool as high-level shocks over a
short period of time. Therefore, when shocks are at shock level 1, you must monitor the length of time
at that risk level. If the shock risk level reaches level 3, you must take immediate action to mitigate the
shocks. Accumulated time of shock at level 3 greater than 30 minutes is exceeding the tool
specifications. The MWD tool will not see all of the shock being experienced by the tool. The crew should
also be aware of other indicators of downhole shock and vibration. Under excessive stick-slip conditions,
the rig's top drive will often be heard to strain, as the surface RPM and torque exhibits low frequency
oscillations. ROP can be seen to drop in some severe cases of stick-slip.
When the shock levels are exceeded, the crew needs to inform the client and make sure that action is
taken as soon as possible. The first step in management of the downhole shock and vibration
environment is to change the surface drilling parameters. Often a fine balance between surface RPM
and WOB will be required to reduce the shock levels. Ideally changes to RPM and WOB can be made
while the bit is still on bottom but often the bit needs to be picked off bottom and the surface RPM reduced
to zero to dissipate all the energy from the system. The new drilling parameters can then be selected,
and drilling resumed.
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