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Milling through a casing collar
26 March 2015

Hello Folks,

We are planning to carry out a cased hole sidetrack which entails setting a Whipstock using the Trackmaster Assembly with Fastrack mill. The following are the challenges we foresee.

  • We don't have a casing tally: This means there is possibility of milling the casing collar if casing collar locator isn't run.
  • Has anyone milled a collar? Did it take significant longer time than the usual or what was the effect on the milling assembly?
  • Has any one milled a window without running a CCL or having a casing tally?
  • Has anyone milled a casing without cement?

I will appreciate your response in anticipation.

11 answer(s)
NicholasA
Consultant
SPREADAssociates
Total Posts: 10
Join Date: 26/06/11
I Have never run a whipstock without a casing tally only a fool would.Get the relevant information and start afresh.Milling couplings is not a problem if you know where you are. It seems a complete and utter non compliance of measurements is the problem.Go back to basics and start from anew.
KenHorne1
Multilateral Specialist
Multilateral Solutions
Total Posts: 31
Join Date: 30/09/13

Thanks for the feedback Tinuade.  It is good to find out what has happened good or bad and in your case, it seems very good.

My biggest concern about milling a window through un-cemented casing is not the casing coupling but the centralizers.  Milling through a coupling is not something you would do knowingly but as the rest of the group have intimated it can be done it just takes a little longer some times.  The problems can occur when you try to mill certain types of centralizers and stop collars.  Its true you can mill through pretty much any centralizer and stop collar when it´s held rigidly in place with cement but when its free to mover that´s when the risk increases.

Regards

Ken....................

tinuade
drilling engineer operations
Addax Petroleum
Total Posts: 3
Join Date: 10/11/14

Thanks all for the response.

The following operations were executed.

  1. Scraped 9 5/8" casing above and below planned Whipstock setting depth (circa 3,450ft).
  2. Run a GR/CCL log to locate the casing collar and set the whipstock optimally.
  3. Ran the Trackmaster milling assembly comprising of the Tri-mill + Whipstock. Oriented the Whipface using the NaviTrak MWD tool and set the Whipstock.
  4. Milled and dressed the window in 1hr.No traces of cement were observed.
  5. Drilled 20 ft of new formation, performed a FIT, continued milling an 80 ft rat hole in 1.5 hrs. The rathole was to accommodate the RSS BHA, including density / neutron, such that it would not have to be rotated across the window.

The operations went as (or better than) planned without any NPT.

* A number of wells have been successfully sidetracked through uncemented casing without problems (the fact only known due to the lack of cement traces in the returns). However, it was considered that the risk of sidetracking through possibly uncemented casing and potentially through a casing collar was one too far. Had it been known that the casing was cemented at that point, the risk of milling the coupling would have been taken. On each occassion the required FIT was achieved without the need for a cement squeeze.

** Previous experiences of milling the rathole have been unsuccessful due to very slow penetration rates, to the extent that dedicated dual water melon mill BHA runs were planned. In this case the second run was not necessary with the original sidetracking watermelon mill came out of hole within the limits.

Regards,

greaneyt
Consultant
SPREADAssociates
Total Posts: 18
Join Date: 11/01/15
All things being equal I'd expect a collar to mill ok, it's relatively soft material, same as the casing.

I agree with suggestion to run a CCL unless a good reason not to.

You need to consider ODs of the mill & collar and dimensions of the pilot BHA / pilot mill vs Casing ID (how far can the pilot be pushed over).

However for info I had one bad experience, with a different application, using a pilot mill from surface, somehow it got pushed over too far (we'd tried to keep it too centred) and milled very slowly. We ended up getting much better ROP without s pilot.
KenHorne1
Multilateral Specialist
Multilateral Solutions
Total Posts: 31
Join Date: 30/09/13
Tinuade, any update on what you have done or your thoughts are?
hank
fishing tool consultant
SPREADAssociates
Total Posts: 31
Join Date: 13/03/12
Not a recommended procedure particularly in uncemented casing as once the coupling is cut the casing may part or the collar may turn sticking you and or causing an unusable window/csg exit.
It has been done but increases your risk of losing the well.
NicholasA
Consultant
SPREADAssociates
Total Posts: 10
Join Date: 26/06/11
I Have never run a whipstock without a casing tally only a fool would.Get the relevant information and start afresh.Milling couplings is not a problem if you know where you are. It seems a complete and utter non compliance of measurements is the problem.Go back to basics and start from anew. 
KenHorne1
Multilateral Specialist
Multilateral Solutions
Total Posts: 31
Join Date: 30/09/13

Tinuade, to your questions there are many other questions you need to share the answers to.

Is this a straightforward sidetrack or a multilateral you are carrying out?

What size, weight and grade of casing and range of casing joints are in the hole?

What size hole was the casing run into and what type and how many centralisers are attached to each joint?

What is the hole angle you will be setting the whipstock at? 

What orientation do you plan to cut the window at?

You ask if anyone has milled a window with no cement, from this are we to assume you do not have any cement?

Are there any signs of pressure in your B annulus?

p-j.palten
Drilling Supt
Nostrum Oil & Gas
Total Posts: 44
Join Date: 14/11/10
agree - different type of dwarfs, high lateral vibrations during milling the coupling or millling with no cement behind the casing causing a shark teeth profile - most likely a second mill run will be necessary -  apart from that pieces of a centralizer could be milled / pushed to the side causing hang up of the directional BHA afterwards. That means a CBL/CCL log and selecting the right top of whipstock is much more cheaper than all the trouble you get afterwards not doing it. Of cause it depends as well on what steel quality you plan to mill. Do a calculation for the wireline and BHA on stretch due to different weight and material and area to see how much difference it could be and correct the depth to run the right whip stock position.- You can add an active gammaray radiator on the whip stock to correlate depth.  Did you run a LWD tool in the past with logging started already in the casing section ? You can see the couplings in the difference in gammaray as well because of different dampening/wall thickness.
rockbit
Consultant
SPREADAssociates
Total Posts: 13
Join Date: 31/07/11
Collars are millable, just a little slower.
A CCL is a good idea, but I've done without.
If your casing is not well cemented, it is a good idea to run a piloted mill to keep things lined up, or you run the risk of premature sidetrack.
acraven
Project Manager
Myspread Users
Total Posts: 17
Join Date: 04/07/08
I have milled through couplings before when well geometry and architecture has forced us down that route, but would always prefer not to if you can help it. There will be additional time to mill and may result in higher vibration which may risk damage to the inserts on the mill.

Milling couplings will be harder if the casing is unsupported as there will be less stabilisation of the window as it is created, resulting in higher vibrations and further risk of mill damage. Unsupported exits have been before done both intentionally and unintentionally with very little issues observed. Window edges will be rougher and more likely to bend back and possibly shear off in larger pieces.

For all the extra effort involved, I would suggest running a CCL/CBL log to optimise kick off location though
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