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13-3/8" x 13-5/8" Deep Casing Landing & BTC Connection
22 December 2020
Dear All

We are at the planning phase of our deep well project that demands landing of intermediate 13-3/8" 72# P-110 (BTC Connection) (Surface - 1200m) x 13-5/8" 88.2# Q-125 (TSH ER) (1200 - 4000m) casing to 4000m MD/TVD.

I have done my calculations manually and through software, and it is satisfying the required loads for casing body. However, since it is BTC casing at the top, I am afraid about the axial loads during running for such a heavy string (Dry Wt: 496MT & Buouyed Wt: 389MT). Jump out of connection is my main concern as there is no fixed make up torque value and depends on triangle. If it breaks, then there is no way to bring back the casing to surface due to the limitation of DP overpull capacity.

Further data: Normal PP throughout well. Last shoe at 2100m. MW: 1.70 SG. SF of 1.5 for both casing and connection.

Does anyone have similar experience in running BTC connection to such a deeper depth? Any words of wisdom? I would appreciate it.

Thank you.


10 answer(s)
SPREAD Associates
Total Posts: 164
Join Date: 05/03/08
Hi Shah,

You should not have an issue with BTC for a heavy string as long as it is properly made up as noted by other posters on here already.

However, I would consult with the original manufacturer before doing so.

It used to be the case (perhaps not now - I don't know) that they did not recommend using a BTC thread on any grade higher than 80ksi.

This was because the BTC thread form has a 'relaxed' tolerance compared to a premium thread, and as a result the uneven build up of hoop stresses could shatter the coupling if it was a higher grade than 80ksi.

One question, if the 13 5/8" 88.2lb/ft Q-125 is needed just for collapse, why are you running it so far up inside the previous casing shoe?

All the best!

Drilling Consultant
SPREAD Associates
Total Posts: 70
Join Date: 15/09/14

I had never run such a long string of 13-3/8" casing. But had run 9-5/8" Buttress casing up to this depth before. For over 37 years, had never seen a buttress casing that failed prematurely on connection. 

13-3/8" buttress casing make up torque should be around 12-13k ft-lb, depending on manufacturer. Of course middle of triangle is what I normally make it up to. 

Other factors such as high deviation and type of mud could be additional factors to consider. 

Of course just need to take a little more time to clean the hole before running the casing. 

Drillling Engineer
Pakistan Petroleum Ltd
Total Posts: 5
Join Date: 03/08/19
Hi All.

Thank you for making some good points and asking further queries. 

- Using BTC connection just for the sake of consuming old inventories and dont want to order new casing or cutting threads from third party due to liability issues.

- It is an intermediate casing (not production casing) and designed to run in 17" hole size so there is no need to use gas-tight connection and no presence for sustained casing pressure problems that may jeopardize well integrity.

- Regarding not using the high rated casing at the top: burst load is not high at surface and satisfying the loads. However due to high collapse requirement, thick walled casing is used at the bottom.

- Frac gradient is high, so ECD wont be an issue during cementing or circulation. (hopefully)

- We usually do thread inspection before running casing, especially for BTC connection. 

I am still unable to find the use of BTC connection for heavy loads of casing running operation. I would also appreciate if someone may share their hands-on experience.

Thank you.


Drilling Consultant
Crescent Petroleum
Total Posts: 3
Join Date: 23/12/20
Shah, API threads are for low cost onshore oil producers, not hi-end project like yours. They have a higher risk of cross threading and they are not gas tight. The seal is provided by the thread compound which will disintegrate over time and you may have long term integrity issues. 

If you can, re-cut the BTC to a premium connection.

The attached list is 13 years old but still a good reference.
Documents uploaded by user:
Approved Connection List.pdf
Managing director Punch Energy Services
Punch Energy Services
Total Posts: 18
Join Date: 24/06/20
Hi Peter,

Guessing they run this in the bottom for the higher collapse rating.

Also wonder what hole size they will drill, pretty long section and to run the larger casing size in the bottom part it could result in ECD issues.
Drilling Supt
China National Offshore Oil Corporation
Total Posts: 18
Join Date: 24/09/09
How was is going of the casing runing?runing this casing string need a long time. wellcontrol issues should be considered. how to shut in the well, how to kill the well, how to do the drills, etc.
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 502
Join Date: 10/01/05
'Burst if first' typically in design where higher grades are generally run on top.

This is not in your case?

Why is this so? 
Inquisitive to understand the design rationale behind this.

Managing director Punch Energy Services
Punch Energy Services
Total Posts: 18
Join Date: 24/06/20
Hello Shah,

First question that comes up in my mind is, why run BTC casing?
There are many (good) alternatives and not be default a lot more expensive.

Tension rating can be calculated.

Next to tension, would be good to check compression rating for such a long string (if well is heating up in production)

If the BTC pipe selection is price driven, I guess it is a good approach to;

1st - Ensure Well mechanical integrity (even if this requires a more expensive premium material).

2nd - Optimize Well costs

Please realize that >90% of pipe failures occur in the connection
Well Construction Lead
Total Posts: 26
Join Date: 27/02/16
Hi Shah

Never done it, but there is an Exxon SPE paper dealing with N80 72# BTC casing strain tests, that can help.
SPE paper :

Document ID SPE-5598-PA
Publisher Society of Petroleum Engineers
Source Journal of Petroleum Technology
Volume 28
Issue 11
Publication Date novembre 1976

Total Posts: 117
Join Date: 10/04/08
Shah Kamal, could you consider using pre-use load tested float equipment and partially float your casing string in to reduce the hook load. It is after-all the reason that float equipment was invented 100 years ago. Of course this only assists whilst running and after landing when you completely fill the casing the full load appears. I suppose you could continue to computer analysis and torque turn your Buttress casing to help ensure full and proper make-up. 
Posted by

Shah Kamal

Drillling Engineer

Pakistan Petroleum Ltd

Total Posts: 5
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