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Sidetrack with whipstock in 7in casing
06 December 2013
Hello dear friends!

We have experienced restriction in running 4.75 RSS through window after opening window with Fastrack Tri mill. Does anybody have experience how to solve this problem?

11 answer(s)
DSL (Drill Site Leader)
Abu Dhabi Marine Operating Company
Total Posts: 48
Join Date: 20/04/11
Recently (last month) we set 7" cased-hole whipstock with 2deg whip face, Length of whip face was 14 ft.

We set the whipstock @15 deg right high side. Whipstock was set @14400'md, hole inclination 80 deg. We opened the window across dolomite and drilled 20 ft rat hole. Then we run directly with Baker autotrak and motor. Assembly passed window easy and drilled 6" hole. 1400 ft.

BHA was 6" bit- 4 3/4" Baker autotrack rotary steering, motor, MWD, resistivity, drilling jar 4" drill pipe & 5"" drillpipe to surface. 4" drill instead of 3"" drill pipe. We used 9000 ft of 4" Drill pipe because window @14400 and top 7" liner @ 8000'md. Every thing went fine, but free torque was too high 19000 ft-lb, drilling torque was also too high at 26000 ft-lb . However we retrieved the whipstock without problem (to access the lower drain).

In summary, for low whipstock inclination 2 deg with long face help to pass any stiff bha.
Multilateral Specialist
Multilateral Solutions
Total Posts: 36
Join Date: 30/09/13

Chen.  I think you need to be a lot more specific and provide more accurate details of what your problem actually is.

You say you experienced a restriction passing through a window with a 4.75” RSS. 

Did the mills come back within acceptable gauge size?

Do you know how long your milled window actually is?

Are you hanging up and if so is it at the top of the whip or the bottom of the window or are you just losing some weight but can pass through?

What is the hole angle and what is the whipstock orientation in relation to high side?

What size bit are you running on the RSS?

Was the widow fully qualified before pulling the milling BHA out of the well, could you run the milling BHA through the window with no rotation and no pumps? 

Did you generate a rathole and if so how long?

You say you are experiencing a restriction but does this mean you can still pass through?

The more information you supply the better the responses will be.

Total Posts: 2
Join Date: 25/04/10

Why not look at undergauge hole size through window. If your drift is 6.000 then drill a 5.875 hole thru 6.00 window. Whenever possible (and practical) drilling slightly undergauge hole thru a window is the preferred option.


fishing tool consultant
Total Posts: 37
Join Date: 13/03/12

  Not enough facts to discern the reason but these days guys are not so much cutting a window but "can openning", milling with too much weight and /or not holding penetrations rates back to "hold" the mills on the ramp particularly once past "centre point" where the chances of jumping the ramp increase.

Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 361
Join Date: 10/01/05
This is a very common failure where there are several reasons that could have caused and effected the end result.

Was this recognised as a risk? If not there is an issue in your safety / risk management process. 

If it was recognised, as stated this is very high on my list in such a task. What was being done to prevent this recurrence because it is quite a common failing. I.e failing to drill ahead with a directional assembly after setting a whipstock, milling a window etc. the objective first and foremost is to kick off and then if risked as achievable, then directionally drill ahead. Too often a rss etc or similar directional bha cannot achieve this. It's often risked as a two trip job!

In this case, why did the RSS BHA  not go through the window and rathole is most likely purely geometrical and/or due to dogleg incompatibility of bha pulled, casing well ore, and bha geometry etc then run.

Most common reason and issue is that rathole drilled was too short and/or ramp design, milling etc best practices and milling bha applied were not optimal to accommodate the bha that followed.

Note: A lot of planning and extra engineering is normally required to assure success in such matters from my experience. Where only those involved can comment in this respect. 

This lost time event, simply did not just happen,  but fact, was caused, where there are reasons that only the team involved should be investigating to conclude the physical and human factors involved, to collectively learn from what and why operations failed as planned.

Where without knowing the exact details of your well. E.g
Inc'ination, formation types being kicked off, whipstock info, milling bha, orientation of window, how this was achieve, bha that followed etc we can only second guess. 

I would recommend getting an experienced fishing supervisor or an old drilling guy, to have a look at all your data and evidence to get to the warning signs ( mills being pulled out of spec etc)  that were present and then to the physical causes and latencies of the team involved. 

Our problem as an industry is that too often we don't learn from these events, and when we do why we then struggle to find better ways to remember. SPREAD thus a valuable resource for those who choose to remember.  
Sr. Drilling Engineer
Total Posts: 8
Join Date: 05/09/14
Dear, I am sure you have checked the gauge of your mills after you pulled them out. As suggestedeither you can try a window cleaning with another full gauge mill. That shall help you. On the other hand try to drill some rat hole if the mills permit.20/ 25 ft rat hole will not cause you any harm even though you want to drill directionally. The most important that I would like to know is the hole angle at the window and the orientation of the window ( degrees right or left of high site along with a complete BHA details and the exact depth where the drill string hangs. Also I'd it is hanging on RSS Pads you shall see some marks on them. I hope you understand what I am trying to find. Contact me if you need more help on xxxxxx. All the best Regards Milind
Note from moderator:

We have removed your phone number, because we would prefer that everyone on the forum benefits from the exchange of ideas.

Milind, thanks for your input. If you have colleagues who would like to join our Free forum, of like-minded individuals, we'd be delighted to welcome them after they register. Just get them to quote your good name and approval will be automatic.  Best wishes .. Dave
DSL (Drill Site Leader)
Abu Dhabi Marine Operating Company
Total Posts: 48
Join Date: 20/04/11
Dear todden.
I agree with you,I would like to add very critical point in case that problem happened.
First where will set the whipstcok and how much original hole inclination.
If the old hole inclination from 0 to 60 deg at setting depth, we can set whipstock which has ramp or face inclination 3 Deg, in that case any BHA will pass easy without problem.
If the original hole inclination from 60 deg to 90 deg .we will set whipstock face inclination 2 deg or less that 2 deg.
I meant by all of these points the inclination of whipstock face is the key of success to set, open window, drill ahead with any type of BHA if we consider this point.
We discovered that from our problems whipstock. Only the disadvantages of changing whipstock face inclination the rat hole below the window.
If the face inclination 3 deg rat hole below window will be shorter with high dog leg.
If the face less that 2 deg the rat hole will be longer with low dog leg.
Total Posts: 19
Join Date: 31/07/11
In my experience, stack up the string reamers when you open the window.  Then it acts just like a dogleg when running future trips.
Head drilling Operation
Total Posts: 3
Join Date: 10/02/10
Dear Chen

We had this problem with one of our Re-entry wells in offshore and by using a stabilizer solved the problem and passed through window.

PLM Fishing & Remedial
Total Posts: 1
Join Date: 29/12/13

First, what was the gauge loss on the mills that milled the window ? If undergauged,I would say if more than ¼", a remedial trip is required to ensure that window/rathole is in good condtion.Factors affecting the mill wear such as the formation type and the length of rat hole that was drilled should also be taken into consideration.

If the Fastrack Mill completed the window but failed to complete the rathole due to the compressive strength of the formation and provided that the Follow Mill on the Fastrack Tri-Mill has passed the bottom of the window i.e. the window is essentially complete, then it is recommended that a bit (IADC Code 117 or IADC Code 447 or similar) is run instead of another Mill.

If there is a substantial amount of cement to be drilled out - following a remedial cement job, it is recommended that a Tri-Cone Bit (IADC Code 117 or IADC Code 447 or similar) is run instead of a Mill.  The Bit will perform better whilst drilling out the cement.

Was the whip set in vertical or horisontal well, and what was the orientation of the whip ? Another things to consider is the length of the rathole,as some RSS BHA`s require longer rathole than others.(I have no info on what type of the RSS BHA in your application).We run RSS assemblies( all suppliers) across our whips on a daily basis without any issues, so unless you ran a special BHA, this should not be the reason why you experienced problems.

Always take care at all times when passing through a window with any bottom hole assembly.

  • Bent housing motors should be orientated in order to allow them to pass the window without hindrance.  This should be carried out above the whip face.  After lining up the toolface the pumps should be switched off before sliding through the window.
  • If it can be avoided, drill bits and stabilisers should not be rotated down whip face.  Where this is not possible then the rpm should be reduced to the minimum acceptable rate.
  •  PDC Drill bits should not be rotated down the whip face.

It has been observed that very occasionally a drilling assembly requires to be ”œwalked” past the Top of the Whip to allow the drilling assembly to pass through the window.



senior drilling engineer
Kuwait Energy
Total Posts: 14
Join Date: 29/11/13
Dear Chen

You can try another tri mill run with full gauge mills. The process need to be repeated if mills pulled out undergauge

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