Installing Disconnectable Turrets and Offloading Buoys – OTC Paper now available
Installing disconnectable buoys and offloading buoys is made easier and quicker using ball and taper subsea mooring connectors within the primary mooring lines, reported Brian Green, General Manager, First Subsea, at this year's OTC conference. The joint paper, prepared by Brian Green and Keith McClure, Nexen Petroleum U.K. Limited, reviewed how cost and time pressures on installation and field operations, together with health and safety concerns, are encouraging new methods of subsea connection that reduce the cost and complexity of pile and buoy installation, yet also provide on-going operational benefits.
 The use of FPSOs with STP (disconnectable submersible turret production) or BTL (bulk turret loading) buoys has created a demanding environment for chain and shackle installations leading to increased installation time, equipment and vessel costs. Subsea mooring connectors enable installation of piles without the need to use large vessels and no requirement for diving operations, resulting in a safer operation. Mooring pile installation and mooring line installation can be carried out in different campaigns and from different vessels.
Subsea connectors also reduce the number and size of tugs required to facilitate hook-up of STP and BTL buoys; tugs with minimal bollard pull are used to manoeuvre the buoy to facilitate hook-up of the last mooring lines. No diver intervention is required to carry out the subsea connections. And safety concerns that arise from making up connections on the back deck of installation vessels are avoided. Moreover, disconnectable turrets and offloading buoys can be installed later in the project cycle; and with simpler mooring line arrangements, thus avoiding damage to other structures in the field and the environment such as coral reefs, during tow out.
In a recent development, subsea connectors featuring an on-board CCTV have been used to remotely find and connect a mid water buoy, providing easy retrieval without the need to search for a floating rope, ROVs and diver intervention. The connector systems allow an operator to abandon turrets in the event of tropical storms or temporary abandonment, retrieving them later once the vessel is back on location.
The OTC paper also touched on the implications of subsea mooring connectors on subsea field architecture with particular reference to the more efficient installation of Mid Water Arch Buoys.
Copies of the 'Installing Disconnectable Turrets and Offloading Buoys' paper, ref: OTC-19709, are available from the Society of Petroleum Engineers. Visit www.spe.org, and follow the 'Papers / Publications / Authors' link.
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