Well Integrity Technical Section

Dear Community Members and SMEs,

We are experiencing challenges with parting of the 30" conductor casings on an existing fixed platform. The conductors were driven in place and are uncemented on the outside. The first parting occurred on empty casings that were driven in place, for future production wells but never drilled and completed. Fairly recently, leaks have developed on production wells. It appears that the parting is occurring at the welded connections between the lengths in and around the splash zone and sections in air. Can anybody offer advice on what the normal maintenance requirements are on such casings? Any standards or recommended practices we can refer to? What are some of the immediate steps we can take to arrest future incidents? Please note that the location of the platform is remote and the only mitigation right now is annular fluid top-ups.

Regards

Hi, there is a company with expertise in remediating corrosion (holes) in platform legs, which is a similar problem to yours.  They are called Nautec and they may be able to help.  You can probably Google them

From the way you mention that empty casings have also failed and that the problem appears to be at the welded section between conductor lengths suggests that you have a fatigue failure at the welds. Do you have access to a fatigue analysis that considers both the cyclic stresses which occurred during driving and those generated by wave loads on the conductor. If you dont have a fatigue analysis in place, I would suggest you get one performed to look to quantify the issue, please contact me if you need more information on this. 

If you have the driving records for the conductors, they are also worth reviewing, if they conductors have been near refusal towards the end of the driving process then you can generate a high cyclic stress from the last period of hammering, all of which is passed through the marine section which will then see the wave loads.

For fatigue related rather than corrosion issues at the welds, you may need to install some form of clamp which provides local support at the problem location and acts as a load transfer mechanism from one joint to another taking the load away from the weld. These can be either bolted, welded or grouted in place.

If you have any future conductors you plan to install, possibly consider the use of premium threaded connections rather than welding the conductor. The installation will be faster and any conductor to connector weld will have been performed in a factory rather than at site and will have a far better fatigue performance.

Please let me know if you have any questions on the above and I will look to answer.

Regards,

Stewart

Hi Stewart,

Thank you for the response. I have uploaded a pdf file summarizing some of the info on the conductors. It appears fatigue analysis was performed on the conductors during design. You will notice from the pictures that there are half shell clamps installed. I am not sure if they are transferring the loads generated by the impact of the waves. I do have a summary of the driving records, but I will need to do some more digging to find the welding information. Design spec indicates 100% MPI and UT.

Regards

Amin

Attachment(s)

FA Platform Well Condutor Guide-Sleeves Info.pdf   1.03 MB 1 version