Remote Intervention & Leak Repair
Project
WW16 Leak Repair Scope
Location
West of Shetland, UK
Water Depth
360-550m
Project Type
Remote intervention repair of a subsea asset
Vessels
Normand Subsea
Project at a glance
Phase 1: A leak was discovered from the WW16 water injection tree assembly. The source of the leak was found to be a ¼” NPT port on a mounting block, fitted to a flowmeter spool piece within the tree structure, with very difficult and limited access. We removed initial steelwork and grating to install the first leak repair clamp behind ballast weights.
Phase 2: To mitigate further leaks from the remaining ¼” NPT ports, the entire mounting block, DP cell and sensor cable assembly were removed from the flowmeter spool and two bespoke leak repair clamps were fitted to seal the flowmeter spool ports.
Highlights
- SIT to help define installation and deployment methodology and prove 1st clamp design
- Offshore preparation of site by removal of flowbase steel work to gain access to leak location
- Installation and testing of 1st leak repair clamp
- Removal of ballast weights to gain access to flowmeter spool mounting block
- Removal of DP cell and sensor cable from mounting block, leaving CP system intact
- Removal of mounting block to expose flowmeter spool HP/LP ports
- Installation of two bespoke leak repair scissor clamps over the HP/LP ports
- Subsequent leak testing of the WW16 flowbase prior to re-instatement of water injection system pressuregain access to flowmeter spool mounting block
Scope of Work
Phase 1: Subsea 7 was tasked with fitting and testing a bespoke leak repair clamp. This was carried out successfully, however a secondary leak was discovered from another failed ¼” NPTport on the same mounting block.
Phase 2: The exposed two ports on the flowmeter spool were then sealed by installing two bespoke leak repair clamps. The new system was leak tested allowing water injection to resume at the tree.
- Engineering & tooling development to remove grating, external framework and structural steel as required to gain access to phase 1 leak location.
- Engineering & tooling development to remove ballast steel, DP cell and sensor cable assembly and flowbase spool piece mounting block to gain access to phase 2 leak location.
- Phase 1 and 2 SITs to determine methodology, test all bespoke designed tooling and prove execution sequences.
- Installation engineering of sealing clamping solutions including procedures and HIRA.
- Interfacing with 3rd party equipment to determine ancillary equipment required and operational parameters.
Technology and Innovation
Being able to define, prove and execute a successful leak repair project using remote technology/ROVs proved a significant cost saving to the client. The alternative option to effect leak repair was to utilise a drilling rig to recover the tree to surface, repair the leak and re-deploy the tree.
Project Milestones
- Initial installation method defined and tested during SIT. Learnings from SIT incorporated into offshore execution.
- Successful offshore execution of phase 1.
- Identification of a further leak path post phase 1 leak testing.
- Installation method defined and tested for phase 2 repair operations – method defined and tested during phase 2 SIT.
- Successful ballast weight removal, removal of DP cell and sensor cable assembly followed by mounting block removal to gain access to the spool LP/HP ports.
- Installation of two bespoke scissor leak repair clamps c/w dedicated anodes.
- Leak testing operations to confirm successful clamp installation and seal positioning, followed by re-instatement of water injection pressure to the tree.
Collaboration
Internal provision of SIT site set-up and support, and ancillary equipment used to prepare the worksite and install the leak repair clamps. This included utilising the same equipment to be used on another leak repair workscope, which helped simplify mobilisation and offshore operations, as well as passing equipment savings on to the client. Subsea 7 closely collaborated with IK (Norway) who designed the leak repair clamps for both phases.
Worksites
Subsea 7's Greenwell base facility was used for all SIT operations and support and equipment testing and mobilisation. The MSV Normand Subsea was used to complete all offshore operations.
