Cut & Pull 9-5/8" Casing
17 March 2010
We are looking to cut and pull old 9-5/8" casing from several platform wells in the North Sea.
The wells were constructed back in the days when it was normal practice to cement casing strings up inside the previous casing shoe, however, the actual top of cement is a little vague as 9-5/8" cement records are incomplete (unknown losses) and the CBL logs are typically inconclusive. There is OBM with 25% solids left behind the casings and the casings have been landed with a Vetco slip-and-seal type hanger.
The million dollar question is at what depth could we reasonably expect to be able to retrieve 9-5/8" casing strings from these wells?
Any guidance / experience on the cutting and pulling of 9-5/8" casings and the retrieval of Vetco slip-and-seal hangers thru the BOPs would be greatly appreciated.
There was a presentation at the DEA Europe in March 2010 (Aberdeen) on this problem, how the operation was approached and a review of the results; unfortunately I don't have the paper or recall the presenter, but you should be able to find it.
From memory the advice was use the Top of Solids as indicated on the CBL as 10+ft of solids precipitated out of the mud is enough to prevent pulling of the casing regardless of the top of cement.
If this is just a side track, why are you pulling 9 5/8"? We routinely cut windows thru two strings of casing these days.
I would stay away from pilot milling unless absolutely no other route as sometimes it goes as planned and sometimes it don't, identical scenarios and set ups, same rig even...... you need a good rig, special considerations for straight flow lines, no butterfly valves,flow line cleaners, collection of iron, jetting bops, hi yield polymer mud, magnet downstream of the shakers the list goes on. Some of those"new" rigs have issues with feeding off drilline consistently and with the short solid milling strings you would/could be making some nasty steel wool type cuttings that are difficult to clear, cut an pull as much as possible. I have had where we went milling and after a half joint the string started turning, we went in jarred and pulled to the next cut and the rest was just spear jar and pull but that is more the exception than the rule. What ever you do you can almost certainly bet it will not be exactly to plan. Good fishin!
The above remark refers solely to 2-step uniheads i.e. unitised spool with a bottom prep for 13 3/8" casing a mid shoulder for the 9 5/8" production casing and an upper shoulder for the production tubing hanger.
For the most common spool type heads where slip & seal assemblies are often used, the BOP must be taken off to install the slips around the casing (Only one Operator splits the BOP to have at least one casing ram to rely upon, inserting the slips).
So no 13 5/8" BOP can be installed to retrieve the slips (unless a single ram preventer). This as the slips may catch the ram cavities and stop their ascension.
The Gray wellheads had a good reputation in the past. Hence their popularity in the 70s/80s. So there should be a lot of experience among the differente operators in cutting/retrieving Gray slip & seal assemblies. Maersk Oil & Gas could help in this stance.
If you use a seat protector, with the same ID of the seal area of the slip and seal assembly, and then cut the 9 5/8" casing, the topmost coupling will bring the assÂ´y casing + slips all the way tucked inside the special seat protector with a top No-Go profile.
Wrt the cut depth you should try first the level more convenient for final abandonment, well inside the cemented area of the 13 3/8" casing; failing that aim at cutting at the 13 3/8" top of cement.
Bear in mind what the Country regulations say about permanent abandonment.Most likely a cement plug inside the 13 3/8" casing near its ToC will do.
We did a lot of slot recovery in Egypt and Abu Dhabi. After abandoning the well, You can N/D the 9 5/8" casing spool or housing, then run with mechanical cutter and cut the 9 5/8" by 6 ft below the 9 5/8" Casing spills, then run with casing spear and retrieve the cut off. In case the cut off is not working and the slips are stuck so go direct using a welder torch to cut the casing below the slips (Dry one ft of the casing to use the torch inside the 9 5/8” casing, make circle cut inside the casing, below the stump by +_0.5 ft deepened on slips length, exactly make this cut below the slips), then make a vertical cut by the torch and easy the slips will come out
For 9 5/8" Casing in case the USIT shows good bond behind the 9 5/8" Casing so milling is the best option, therefore you have to plan very well handling the casing junk which is coming from milling the casing. The big problem is plugging the flow line from the junk. We have a good experience in milling 9 5/8" casing and 13 3/8" casing by using smith and weatherford equipment., average milling rate for 9 5/8” 47#/ft is 5FPH. Milling +_ 300 of 9 5/8” casing 47#/ft , of course milling will start from surface and can cost about 200,000 $ US; this includes only the Smith milling equipment plus MiIilling fluid. You can add your rig cost for milling +_300 ft of 9 5/8” casing is about 5 days
0. I have been retired for 12 years lnow so my picture cn be dated.
1. You mention North Sea Platforms and GRAY [Vetco] heads.
My recolletion brings me a standard platform with BOP deck far above the wellhead deck. You refer to a GRAY slip & seal assembly.
It seems inconsistent as GRAY had some 40.5% of the North Sea market using Multibowl design. This works best with mandrel type hangers - slip type the exception.
If indeed slip & seal assembly are the rule they were installed by splitting the well head to install them. The distance Rotary table wellhead may give room to a casing coupling somewhere and the GRAY slips could not ride it; hence splitting the head to install them.
Assuming this is the case it is better to review the installation manuals on how to retrieve the slips; most likely you have to split the head.
2. Cutting the 9 5/8" can be done mechanically, explosively, chemically and hydraulically. I would avoid the mechanical cut as I fear rotating the casing above and unscrewing it above the cutter.
[By the way, do you have Premium Threads or API ones? These are more prone to the inconvenience stated above...]
I would try calculating the Free Casing Point by streching the casing and giving the allowance to the volume of solids cut right above. Be prepared to repeat the procedure a few joints above
Here's the attachment that Tom Macrae refers to .. I'd like to thank Tom for this contribution.
Fully agree with the USIT comments, found it very useful doing tieback recovering deepwater GOm for Shell.
Avoid multiple cuts in one trip, if you pull out the pipe cutter and the carbide tip is gone, which cuts are made and which aren't?
For milling we had a lot of success (1000ft of 10 7/8" 72#) with 5 large blades on the pilot mill, designed a fairly loose pilot mill to allow a little bit of walk. (Again the need for this will be born out by the USIT which can show if you have casing to casing contact), also 5 degree back rake on the mill blades seemed to work well.
One of your biggest problems will be if you have coupled pipe as the connections form barite settling points and it ends up being like trying to pull a knotted rope trhough your hand, at that point you might end up at cut and pull 1 joint at a time versus milling.
Our experience of this is that there is no reliable way to predict what you will encounter. If you cannot get away with enduring a smaller hole size, then plan "what if" scenarios. Flow diagramme end up being essential Hope for the best, but plan for the worst.
Merlin ERD Ltd
I planned and executed the North West Hutton Casing Recovery programme when BP abandoned this platform. I was also involved in ATP's slot recovery programme in the SNS. Main lessons from these were: a USIT log will give you your best indication for your first cut - expensive but worth it if it saves dayrate; after you get the first lot out and are still far above required depth, it works out quicker and is much less problematic to cut short 100 ft or less sections and jar them free rather than milling - the swarf gets everywhere and leads to pump probs, drain probs etc, etc. My advice would be to avoid milling if you can, but if you have to, speak with Brandt in Aberdeen (Jamie Shakespear) as they have some good kit for collecting and separating the horrible stuff. I have sent Dave Taylor a presentation I put together on casing recovery when working on the ATP job. He can forward if required.
I agree with Dave to get to the depth required to kick off.
I would first run a cement evaluation tool.
Cut and Pull hanger.
Cut and pull as much as one can, that is free or could like be work and pulled free.
Then lots of Milling to depth required. Main problem being that in the old days, these wells had far more vs less cement generally pumped.
Note: We have however far better milling technology today so this is a far more effective and efficient process.
Milling casing lessons learned? I suggest SPREAD raises a seperate discussion for this and we can attach what we have learned. (note: there is lots!)
One simple thing that I´ve done to determine cut and pull depth of casing before is to compare theoretical vs. actual volume cement pumped. I experienced the same thing with you that the drilling report didn't capture about losses during cementing operations. I did some probability after comparing the actual total volume pumped vs. the theoretical and come up with TOC. The probability that I´ve made is related to % wash out of well bore during drilling. It was succeeded and no need to run CBL/USIT or even Free Point Indicator. Hope this works for you too...
Snr Drilling Engr
As Trevor points out you will need to lift the BOP to get the slip&seal hanger our of the way (if that's what it is). Even if you think it's a 'proper' hanger than than an emergency one be careful as the well file may not reflect reality ! The seal seagments and binding wires on the hanger may have deteriorated - quite often the slip segments bind to the casing, but then all fall off (with the risk of going down the hole) as the hanger is in such a poor condition. Hopefully you can get the required barriers before going onto the well with the rig and use your well services crew to effect P&A of the lower portion of the well off-line, but sometimes strange things happen. I have seen one case where the 9-5/8" casing had dropped thru' the wellhead and we were testing the 'B' annulus rather than 'A'. Give me a call on 01224 565603 if you wish to discuss further.
current project I am on we have been cutting and pulling 9 5/8" for sidetrack purposes. Our own well data was vague therefore we took a lesser performance stance.
It might be worth considering running a usit log to identify TOC, barite settlement and cement channeling. What you haven't mentioned is the depth and angles including DLS above the cut and where the cut will take place.
Dave's suggestion for cutting below the hanger is an option to consider. Alternatively you could try and pull the casing full bore (additional over pull compared to pulling with pipe)or just go ahead and cut, pull a couple of stands, RIH with the spear and attempt to pull free. The latter was the succesful method we used and could clearly see that the pipe was free at the wellhead. You will also clearly know if most probably free should you get returns through the 13 3/8" annulus.
As for the slip hanger you will need to lift the riser and BOP to get access to it, therefor you will need to follow your 2 barrier policy. Removing the slips should be relatively straight forward as there should be threaded holes for lifting eyes.
Finally I'm sure you don't want to mill, but if you have to then that's a different discussion which may also require some specialist equipment.
More the pity you !! When we were faced with similar challenges C&P on Shell platforms, our approach evolve to this :
1. Cut and retrieve the hanger .. this removed a "point of confusion"
2. Run spear assembly (with bored out DC), and then Free-point Indicator thru the tool
3. Run cut and pull assy (Red baron in them days).. packoff to seal below top of stump
4. Cut pipe and break circulation .. if needs be, circulate out the old diesel-based OM
5. Then mill to required depth
I know that companies like Chevron and Oxy would routinely mill thousands of feet of casing to get deep enough for the side-track.
Hope this helps
Relentless Pursuit of Perfection Ltd