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Drilling out 20″ casing shoe with 12¼″ bit
10 February 2013


some feedback needed on the below.

The situation is the following: after casing off the well with 20" casing, we need to drill a pilot hole for FE purposes and then open up the hole to 17" with a separate run. The well is vertical at this point.

We are looking at 2 options to avoid a dedicated run:

  1. single run in 12¼" to drill out the shoe track and then drill the pilot hole - POOH - run and drill with 17" UR
  2. drill 12¼" hole with a non-activated UR in the BHA, POOH to the shoe, activate the UR, clean out the shoe track

I personally dont like much the first scenario, as cement would be falling down on the BHA- which should be ok for drilling, considering the clearances, but could cause issues for the wireline run thereafter.

The second option could be achievable, but we are still confirming availability of the tools in country.

Thoughts? Ideas?



8 answer(s)
UK Country Manager Halliburton Dril
Total Posts: 2
Join Date: 06/05/09
Halliburton also have the XR1200 which is a drop ball activate/deactivate reamer. This would allow you to drill with 12¼" bit and enlarge to as much as 17½. You could either drill ahead and enlarge at the same time or drill the section and pull back to shoe, drop ball and enlarge. There are no presssure drops through the tool so less hydraulic restrictions.
There is also the Dual Reamer which is effectively the same set up with a 14¾" fixed PDC reamer to remove more of the casing shoe above the XR1200. This would enable you to drill out and then activate the reamer and drill ahead without having to do a dedicated drill out run.
Drilling Engineer
Maersk Oil
Total Posts: 5
Join Date: 10/02/13
Hi Elisa,
Looking back past experience,
We did second scenario successfully by placing Halliburton NBR (17" Near Bit Reamer) in BHA, In the BHA (LWD)caliper tool placed to confirm NBR open or not, the only challenge drilling out shoe track with restricted drilling parameter so that NBR does not open up in shoe track and after shoetrack and new formation drilled-confirmation of NBR opened up.
We have track record of several wells drilled successfully with this method.
Regards, Mahesh


Drilling Systems Technical Support-Drilling Solutions
Baker Hughes Inteq
Total Posts: 5
Join Date: 07/07/11
It would be preferable to open the hole while drilling rather than try to drill it & then ream an already opened hole as the lack of a contact point/stability below the reamer will destroy your MWD tools & cause a catastrophic failure within the BHA. Use a bit that is less agressive than the reamer to keep the bit in contact with the bottom of the hole.
 If you cannot do the above, drill the 12 1/4 then come out & pick up a dedicated hole opening BHA. Limit the mass below the reamer & be very careful about using high RPM
 If you underream a previously drilled hole you run the risk of backing off connections below the undereamer while rotating. The reactive torque generated is dependent on RPM & can be substanstial. Low angle , Mass below the reamer & connection size determine what RPM you can use. I have seen 8 5/8 connections back off when rotating off bottom with an underreaming BHA.
Many of the reamer manufacturers have reactive torque charts that give guidlines on max allowable RPM for each collar/connection size. Use them.
Documents uploaded by user:
17.5 in hole section reactive torque.pdf
Snr Drilling Engineer
Total Posts: 5
Join Date: 12/03/10

We are doing this on our next well. We are are drilling a piolt hole below the 18" casing for FE purpose and then stage hole opening from 12 1/4" to 16" and then to 20" to run our 16" liner. SLB has this stage hole opener
Drilling Site Manager
Chevron Corporation
Total Posts: 1
Join Date: 28/05/13
Dear Elisa,
In my experience, I have ever drilled pilot hole 12¼" to open 17½ w/ hole opener(HO)+bull nose, then RIH casing 13â…œ" below casing 18⅝". It is very effective to smoothen the borehole.

I see your case quite similar with mine. These are my procedure:
1. Drill out cement w/ 17½ bit f/ TOC to CP+5 ft
2. CHC out of cement from the hole
3. POOH to change BHA to 12¼" bit
4. Drill pilot hole until next casing point (I guess 13⅜")
5. CHC
6. POOH 12¼" bit to  surface
7. Change BHA into 17½ HO+bull nose
8. Ream w/ 17½ HO+bull nose
9. CHC

I face unconsolidated sand formation so that reaming w/ HO is much effective than using UR. Even, until 40 degree inclination.

I'm afraid if you select option #1 or option #2, you still drill remaining shoe track w/ UR (as you first DOC w/ 12¼") and cement debris could plug your UR's arm. Using UR also results less smooth than using HO+Bullnose, so that affect OH logging.

That's my opinion based on practice in my field. Let me know if you have succeed in using UR :)

Consultant [retired Shell staff]
Total Posts: 249
Join Date: 02/09/05
During my active drilling time the consensus was to to drill the shoetrack with a 17" bit or combination 14 3/4 " pilot bit/17" hole opener. This to avoid not only the problems you alluded but also because some 17" under-reamers/hole openers bodies are larger than 12 1/4".
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 362
Join Date: 10/01/05

Its always a compromise. 

First assure to differentiate between must have and nice to have? If primary target is not in this section then surely this is secondary fruit already. So why waste so much 
company time and money.

I would First talk with g&g and get them to justify that you cannot get the must have data with 9" tools in a 17.5" hole? 

If 12¼ is the only way. Then if formations allow I would run the 12.25 MWD /LWD as the lead BHA and then enlarge (PDF underreamer) at the same time behind in one trip. This is common in the North Sea and Norway when drilling development wells, at higher angles, when formations allow. Thus very deliverable in vertical wells. 
Assuming you are likely in deepwater you are likely in a young sedimentary sequence so you can have your LWD data and hole enlargement in the same one trip is my view. 

Finally get someone who knows how to work a bit/bha systems solution to this from within whatever of the big three service companies you are using. This knowledge and experience is vital to assuring success on all fronts.

The right bit unerreamer design, stabilisation and dynamics modelling is central and key to success. Understanding what is going on then applying best practices rig site then key to delivering on all fronts. 

There is a lot to think about but as stated has been delivered successfully on numerous and repeated occasions.

Project Quality
Total Posts: 102
Join Date: 06/05/09


In a previous life, I was part of a group that did something highly similar to what it appears you have planned:  On a fairly high-cost jack-up, using staged fixed-cutter reamers, the hole was opened from 8-1/2" hole to 16", from ~3,500' BRT to ~4,740' BRT, at ROPs ranging from 10 fph to 50 fph (this was a cored and logged section).

The 'only' issue of significance was a jar twisting off, which was successfully fished on the first try.

From memory, the failure was not attributed directly to the increased torque, though that was obviously a contributing factor.  What the failure and subsequent RCFA highlighted was the jar vendor's lack of a predictive component replacement program.  The vendor only, as pretty much all rental tool vendors do, replaced components detected as failing during the service interval.  Unfortunately, the window of detection for components which are subject to fatigue failure is rarely in sync with the service interval (see attached presentation).

And yes, despite the high cost of the reamers and the fishing trip, the opening operation was considered a success.

Hope that helps,

Dominic Drouin

Documents uploaded by user:
Tool Component Replacement.pdf
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