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Pre-installing under-reamer activation ball
01 December 2017
Dear members

At a DWOP last month, we were discussing the plans to use under-reamers (UR)  in the well.  The primary UR will be a ball-actuated type.  It will be run above the LWD etc.  Below the LWD will be an 'on-demand' UR. They will be used in several hole sections.

One of our senior drill-crew members suggested that we pre-install the activation ball before RIH.  The UR rep said that wasn't feasible, but the drill-crew member stated that it had been done on his rig (reminds me of the saying, "Those who say that it's not possible, should get out of the way of those who are already doing it").

In fairness, we then discussed the fact that as soon as we started circulation then the UR arms would try to activate. This might make it difficult/damaging to drill out shoetracks and so on.

So, please can you share your thoughts and experiences on this suggestion.  Experience (facts) will be more valuable than opinions.

Let the debate begin!


1 answer(s)
Senior Drilling Engineer
Drilling Consultant
Total Posts: 3
Join Date: 03/12/17


We used tandem UR, ball activation on top and flow activation below (rat hole elimination system) for the same reason you mentioned: to have the LWD tools below the UR in small hole section while drilling.

We dropped the ball after drilling out the shoetrack, LOT and when the UR was in OH.

One of the reason as you wrote is not to damage the casing... and also the UR cutters even before starting to open the hole.

In the case you mentioned, they maybe installed the ball before RIH on a subsequent BHA after the shoetrack was already drilled out... or drilled out the shoetrack with reduced flow rate to have an insufficient pressure differential at the UR... But I do not think the time saved by installing the ball before RIH is worth the risk.


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Dave Taylor - SPREAD Moderator

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Relentless Pursuit Of Perfection Ltd.

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