Corocoro FSO Mooring Line Tensioning. Tensioning system design, equipment supply and supervision

DLT Engineering
Reference Project

Construction Equipment
Construction Engineering
Site Services

Corocoro FSO Mooring Line Tensioning

The Corocoro Oil Field is located in the Gulf of Paria in Eastern Venezuela approximately 32 kilometres offshore. The field has being developed using FPSO technology.

The FSO vessel was required to be spread moored in position, adjacent to the production facility by 10 anchor legs radiating from the bow and stern. Each mooring line consisted of a large 36 tonne steel sea bed anchor connected to a 4.75inch diameter heavy wire line, which is in turn was connected to a 5inch studless chain using heavy shackles and link plates. Depth of water at the FSO site was approximately 28 metres.

The installation procedure for the anchors was to pull pairs of anchors toward one another causing them to plough into the sea bed. This operation was designed to induce a nominal anchorage load of 700 tonnes into each line to ensure the anchors were firmly embedded in the sea bed.

Venezuelan contractor, Conar Construcciones, supported by ODL Services Inc were appointed as installation contractors for the spread mooring system. DLT were appointed to design and supply of the tensioning system, together with commissioning and operation of the equipment.

Stage 1.

Stage 2.

Stage 3.

The tensioning procedure involved picking up the ‘live’ anchor line and connecting it to a tensioning beam. This was connected to two strand lines to a pair of DL-S418 strand jacks (418 tonnes SWL each) which were mounted on a support frame welded to the barge deck. The ‘dead’ anchor line was then attached via a tension link beam to the same steel frame on the barge deck. When both lines were fixed the tensioning procedure was started by pulling in slack strand on the live side and slowly lifting the mooring lines into catenary off the sea bed. Both ‘live’ and ‘dead’ lines formed a common tension system pulling the anchors toward one another as they ploughed into the sea bed.

There were 6 cross tensioning operations in total, with paired moorings selected to avoid cross over either during or after tensioning.

The tensioning operations were undertaken in 2007.