Rigless Intervention in the Gulf of Mexico


A newly drilled subsea well in the Gulf of Mexico failed to come on-stream. Diagnostics from the host platform indicated tubing-to-A-annulus communication due to an upper completion production packer failure. The operator, Marathon Oil Corporation, considered several approaches but finally decided to apply the solution utilizing Welltec’s technology.
‘The fact that the entire operation could be carried out as an intervention rather than a workover made this approach more appealing as it was the safest, most efficient and cost-effective option’ says Graeme Miller, Completion Engineer for Marathon. He adds: ‘we had never attempted this type of operation before, but we found the best tools for the job and worked as a team to plan and test everything which enabled the success’.
The water depth at the well site was 2,949 ft and the field was located 150 miles from New Orleans, LA. The job was carried out aboard the Helix Q4000 “Category B” intervention vessel, which deployed a high pressure marine riser to allow access to the subsea well. The toolstring, which consisted of a Well Stroker and a Well Key, was lowered into the well. Once contact was established with the shifting profile of the annular formation isolation valve, the Well Key was engaged with the profile and the valve was shifted closed by the stroke applied by the Well Stroker.


The operation provided immediate success as the well was brought online at ± 8,000 bpd.
The actual turnaround time on the wireline work was 12 days, which is estimated to be a third of time required if a conventional heavy rig had been brought in to do a workover.
‘The job for Marathon illustrated the value of careful and methodical preparations prior to carrying out a job. All details must be thought through before you arrive at the site, although one also has to be able to improvise once on the scene. The concept of intervention from a light surface vessel has really caught on as it provides a much less expensive and quicker approach to well intervention’ says Corey Austin, Welltec USA.