Case Study: Thunderhorse Subsea PLET Reconnect Project

Location: Offshore, 150 miles south of New Orleans in the Gulf of Mexico

Operator: BP

During the rehabilitation of the Thunderhorse field, problems were discovered with some of the welds in the subsea manifolds and PLET’s, resulting in them having to be brought to the surface for inspection and remedial repairs.

Sureclean Scope

Provide manpower and equipment for the removal of existing field joint coating using Ultra High Pressure Water Jetting Cold Cutting application to facilitate NDT inspection and repairs.

The Technical Challenge

Engineering a solution which safely, effectively and efficiently removed the coating (4 inch layer of composite material (polypropylene), without damaging the flow line and importantly contained all water and debris arising from the operation.

Restrictions / Considerations

1) Under no circumstances could we, when removing the composite, make even the slightest “cut” into the actual flow line sections.
2) The area in which we had to execute the project was “environmentally sensitive”, meaning we had to ensure 100% catchment and containment of all  water and debris arising from the operation.
3) Critical Path Timeline.
4) The humidity in the work area during the operations reached 45 degrees at times, so it was crucial our operative’s welfare was taken into account during the “Project-planning” regimes. 

Project

Completed in two phases, phase 1 was effectively the development phase which involved 6 months of extensive trials and technology development to engineer and perfect a cutting solution at the HMC welding facility in Vlissingen, the Netherlands.

Phase 2

Phase 2 was the live operations, offshore in the Gulf of Mexico, where the flow lines sections would be lifted onto either the Thialf (the largest Deepwater Construction Vessel in the world capable of a tandem lift of 14,200 t operated by Heerema Marine Contractors) or the Balder ( a Deepwater Construction Vessel capable of a tandem lift of 6,300 t, operated by Heerema Marine Contractors ) from depths of up to 1900 metres, to allow the removal of sections of the composite, exposing the welds for NDT inspection, remedial repairs, re-coating and re-use as appropriate.

Key Facts

The project was successfully completed without  safety or environmental incident

Success of the engineered cutting solution

Involved 16 Sureclean personnel

Lasted for 14 months

Provided turnover of $2.4 million USD to Sureclean