A leading operator in Western Australia was carrying out a rig move during a drilling campaign. While they were moving the anchor of a mobile offshore drilling unit over live hardware the anchor chain become entangled with a subsea christmas tree and caused considerable damage. After subsea inspections were carried out the extent of the damage became clear; the chain had sawed completely through part of the christmas tree and in the process severed the unitech gas lift connector and flowline off the tree, leaving only a broken API flange weld neck flange in its place. The damage rendered the christmas tree inoperable but, thankfully, the well integrity remained intact.
The client approached Proserv to understand whether the problem could be repaired economically via ROV. The remit was simple; re-establish the unitech connector on the tree and deliver the system in five weeks.
Some of the challenges were significant and included:
Incredibly tight deadline
No tool existed to perform the task
API compliance was to be retained so no modifications allowed
Near 100% redundancy required
Proserv developed a new spool support frame so that the orientation and attitude of the replacement spool could be adjusted to adopt that of the damaged tree. An ROV operated, semi-automated flange bolting tool completed the connection.
The scope of supply included removing damaged sections of the gas lift spool, delivering and supporting a new spool on the seabed adjacent to the tree, and connecting the new spool flange with the existing via a standard API flange. Pressure testing of the completion was required to verify integrity of the
- Provided a qualified, industry standard, bolted flange connection in a subsea environment
- All tooling used for the bolting operation was removed from the spool, guaranteeing enduring integrity of the spool
- Support frame isolated the flange from external loads, and allowed the location of the spool to be adjusted in 3D space