Abstract
In Q4 2012, the 8” Teal dynamic riser required replacement. A project team was assembled to remove the existing riser and install a replacement. The riser was originally installed in the 1990's by divers based on the Anasuria Floating Production Storage Offloading (FPSO). The FPSO facilities that were used to provide diver access into the chain table area to secure the bend restrictor were no longer operational. Previous diver intervention at the chain table had experienced high levels of non-productive time, so a remote removal method to cut and lower the riser and bend restrictor to the seabed was pursued.
The project team initiated a concept study to set the challenge to release the riser from the FPSO remotely to a) reduce HSE risk; b) de-risk project by separating release campaign from recovery campaign and c) perform the work offshore using a very small team (FPSO bedding constraints was one of the reasons the team didn't use an air dive team to do it from the FPSO). The concept selected was largely based on a method used for removal of other similar risers in 1999 albeit that all that remained from that campaign was a PowerPoint presentation. The majority of engineering calculations and drawings could not be located.
The tooling was designed, fabricated and tested in less than 6 months from award of contract to offshore operations. During the offshore campaign, various issues were encountered (e.g. incorrect ‘as built‘ documentation) but the remote removal campaign was a success with both the riser and its bend restrictor being removed from the FPSO without requiring any diver intervention, thus reducing the project costs and HSE exposure.
Lessons learned from the offshore campaign are being captured with the concept being further refined to allow the removal of the riser and bend restrictor without first having to cut and remove the topside riser end fitting. This should reduce the offshore operational time for any future riser removals and remove the risks associated with unknown internal condition of the riser.
