Planning Phase
Once the substation jacket was installed, a rock dumping vessel performed the scour protection around the jacket, but there was still a need for rock installation inside the jacket.
Challenges
- Strong current & Low visibility
- Precise placement of rock dump, especially around the spudcans
- Limiting access inside the jacket – how to get inside with the equipment
- Minimize disturbance to the pre-installed filter layer
- How to maximize efficiency in execution of SOW
- The operation required solutions for monitoring of the operation as well as the ability of working stable independently of the tidal current.
- The ScanCrawler had been utilized within structures in the past and was selected for placing the rock, whilst the 15Te Scanmachine was selected for feeding the Scancrawler with gravel pre-dumped outside the jacket.
Project Execution
SIMOPS utilizing both Scanmachine and Scancrawler
As the images show, the method statement was for the Scanmachine to work with the pre-dumped lumps of gravel, have the exhaust connected to the ScanCrawler working inside the structure and placing the rock dump.
Conclusion / Lessons Learned
- Project executed is a safe and effective matter
- Good project planning together with contractor, big part of the success.
- The rock size was larger than advised/ expected resulting in clogging
- As it was only possible to have one observation ROV and one work class ROV in the water, a lot of docking and un-docking was required of the Scancrawler. The ROVs did a good job, struggling in strong current, shallow water and difficult surroundings (inside jacket), but this slowed down the operation
- Relocating the whole spread with hose connected to both machines worked out good
