Bluestream carries out an integrated decommissioning project by rope access, ROV and diving.

Wintershall Noordzee contracted the SWIFT 10 drilling rig for a multi-year well decommissioning campaign. The first project scheduled for the rig was the decommissioning of the subsea wells. 

Before executing the rig work, Bluestream took several steps to prepare:

• We first repaired the platform control umbilical, which was damaged within the J-tube and therefor mobilised a rope access team to open the J-tube and reach the damaged section of the umbilical. The umbilical hydraulic and electrical lines were then repaired by re-connecting a new section of umbilical, which re-enabled well control from Wintershall onshore.
• Following the umbilical repair, subsea support vessel Stril Server was mobilised with a subsea excavator to dredge the rock protection from around the platform wellhead protection structures.
• After dredging, the same vessel was mobilised with a diving system. Divers removed the top hatch and side panels from the wellhead protection structures, performed integrity checks on the wellhead valves, disconnected the wells from the pipeline, and assisted with flushing the pipeline to the host platform.

After carrying out all integrated planning activities relating to the project, the rig arrived on location. Our divers periodically assisted the rig with integrity checks, wellhead re-entry, XMT and guide base removal. The subsea support vessel then executed several other decommissioning and inspection tasks:

• Removal of 31 riser bends, spools and J-tube bends to allow for the future removal of 10 platforms;
• Final subsea structural inspection by ROV prior to the future removal of several platforms;
• Installation of adapter flanges on the platform suction buckets, to allow for future diverless removal of the platform.

In the completion of the rig activities at the platform, we removed the two 100 Tonne, 120 m2 structures through various activities:

• Divers dredged sand from inside the structure, above the mud matts;
• Divers installed the rigging, complete with a cradle, allowing the masterlink to be perched upright for subsequent diverless removal by a heavy-lift vessel;
• We recovered the structures from the seabed with a heavy-lift vessel and ROV, and transported them to shore to be scrapped.