Ahead of the arrival of the BW Athena FPSO from Dubai, subsea mooring specialist First Subsea has supplied the Ballgrab connectors used to moor the FPSO’s submerged turret production buoy in 440 feet (134 meters) of water in the Ithaca Energy (UK) Limited, Athena field located in the UK North Sea.
First Subsea has supplied 4+1 Ballgrab Series II subsea mooring connectors with a minimum breaking load (MBL) of 6,594 kN to moor the FPSO’s 220 tonne, submerged turret production (STP) buoy. In total the buoy has nine R4 studless chain mooring lines attached to suction anchors. Five mooring lines use chain and wire, while the remaining four lines comprise chain, mid-line Ballgrab connector and wire to the buoy.
“The geometry of the STP buoy’s mooring lines meant that four of the nine lines needed a diverless solution. The Ballgrab connector has an excellent track record for this kind of shallow water mooring in the North Sea,” said Brian Green, general manager, First Subsea Ltd.
Each Ballgrab mooring line installation involved the use of a temporary docking porch or mud mat holding the connector’s female receptacle attached by 240m chain to the suction anchor. When the buoy was in position, the male connectors, attached to the mooring lines, were lowered from the surface into the female receptacles to complete the mooring installation, and the mud mats recovered to the surface.
The Athena STP Buoy is supplied by Advanced Production and Loading (APL), a National Oilwell Varco company. The Athena STP buoy is First Subsea’s sixth STP buoy mooring project. Recent projects have included the shallow water Maersk Peregrino FPSO and the Petrobras Cascade Chinook FPSO, the world’s deepest STP buoy mooring.
The Athena field is situated in block 14/18b in the Outer Moray Firth area of the UKCS, lying approximately 18 kilometres west of the Claymore and Scapa fields and the associated production facilities. Ithaca currently holds a 22.5% interest in the block 14/18b. The field has been evaluated by Sproule Associates to contain 2P reserves (gross) of 24.4 million barrels of oil. The initial rate from the field is anticipated to be approximately 22,000 barrels of oil per day gross (4,950 net to Ithaca) with first production targeted for early 2012. Hydrocarbons produced at Athena will be transported from the BW Athena FPSO by shuttle tankers to the onshore Nigg storage facility, operated by Ithaca Energy.
[mappress] Offshore Energy Today Staff, April 10, 2012; Image: First Subsea