Safety was enhanced through remote operation on the debris removal scope. There was a significant increase in the capacity to move larger amounts of rock dump per day, vessel time reduced, with improvements on environmental footprint and project costs.
The Shell Indefatigable (INDE) gas field lies 75 km off the East Anglican coast in the Southern North Seas in water depths of approximately 31 m, developed in phases from 1970 to 1988. Two blocks are owned by Shell/Esso, which comprise 26 wells, 6 platforms, three inter-field pipelines, two export pipelines and two inter-field umbilicals.
We were contracted to provide support to decommissioning activities, this included:
- Hydrocarbon cleaning of the two export pipelines and one inter-field pipeline
- Injection of contaminated pipelines fluids into a disused well
- Use of an FPSO to remove contaminated liquids to shore
- Cut and removal of all riser base spools
- Burial of pipeline ends and any remaining spans and exposures
- Cut and removal of subsea umbilicals
- Debris clearance at platform locations and along pipeline corridor
- Final acoustic and biogenic reef survey at platform locations
- Handover of decommissioned pipelines to the Shell asset
As part of our overall scope of services, we provided support in the removal of cemented rock dumps around four platform legs. The Scanmudring Scanmachine (subsea hydraulic excavator) was used because after DSV, divers began to remove rock and steel slag conglomerate, it became apparent that after minimal progress another more efficient method needed to be introduced.
Safety was enhanced through remote operation on the debris removal scope, hours of operation per day increased from six and 12 hours (divers and ROVs respectively) to 22 hours. There was a significant increase in the capacity to move larger amounts of rock dump per day (up to 20 tonnes per day on Indea Kilo legs). Vessel time reduced and thus an improvement on environmental footprint and project costs. Acoustic and video mapping of the clearance area and depth at site offered better reporting of as-found, progress and as-built.