Drilling out 30" conductor shoe with 17-1/2" bit x 26" Under-reamer

29 May 2012 Hi folks

Hot on the heels of the recent discussion about drilling out shoetracks with "undersized" bits, here's another one for you.

The plan is to drill 36" hole, set 30" conductor and drill ahead in 26" hole size. However, the rig/wellhead set-up is such that the ID is only 21-1/4" so a 26" bit will not pass through. Hence, we are planning a 17-1/2" bit with 26" under-reamer above.

Our challenges are :

• The 30" conductor cementation will be performed with drill-pipe stinger, which will leave 10-15m of cement above the shoe.
• The U/R is flow-activated, not ball-activated, so it will open if we drill the sheotrack with it in the assy. (Apparently the industry does not have ball activated U/R in this size).
• We are worried that if we drill out the shoetrack with the U/R in the BHA then it will get damaged inside the casing.

So, our plan is to :

• Run dedicated 17-1/2" assy to drill out the shoetrack before committing the 17-1/2" x U/R assy.
• U/R would only be opened once inside openhole.

This still leaves the possibility of cement blocks inside the 30" conductor that have only been drilled through in 17-1/2" size (if they don't break off). Then the 20" casing would not pass.

One "final mitigation action" could be to drill to 26" TD, pull back U/R inside 30" conductor to place it above the "original shoetrack", open the arms and wash/drill/clean out the shoetrack.

Our questions are :

1. Have you done "heavy" work inside 30" conductor with a 26" U/R open and, if so, was there any damage observed ?
2. Did you omit the dedicated clean-out run and, if so, any problems ?
3. What comments do you have on our "final mitigation plan " ?

(Note : we are also discussing a stab-in cement job).

Thanks

Dave

6 Answer(s)

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