Nautilus Subsea designed a custom solution for Cecon Contracting for a riser decommissioning project, involving the removal and retrieval of buoyancy modules from risers and umbilicals.
The riser and umbilical buoyancy modules are removed by cutting the Kevlar straps with an WROV and collecting them into the recovery catcher. The catcher is equipped with a hinged hatch to secure the modules and preventing them from evacuating the catcher. The modules are secured by an enclosed heavy-duty net. The catcher is lifted on vessel deck and the upper frame of the 2-part structure is lifted to easily release all modules and continue for an efficient operation.
The buoyancy catcher has a payload of 25Te and is designed according to DNVGL-ST-E273.
The operation was carried out during Q1 2020 for the decommissioning of the FPSO Dhirubhai-1, on the east cost of India.
The buoyancy modules are released from the riser by cutting the cevlar straps. One of the challenges in the project was to define the terminal velocity for the modules to determine the impact energy on the frame. CFD analyses was performed in both ANSYS and OpenFOAM to determine stability of the object, drag forces and direction. In addition, scale testing was performed to verify the results.