The Regas Vessel

The regas vessel proposed for permanent mooring at the Port Meridian deepwater port will have onboard equipment capable of converting liquefied natural gas (LNG) into a gaseous state suitable for transportation to shore in a conventional subsea pipeline.

The purpose of permanently mooring a regas vessel at the Port Meridian deepwater port will allow vessels without LNG regasification capabilities to use the deepwater port. It is anticipated that this will allow LNG to arrive from global supply sources.

The regas vessel will be permanently moored by means of a submerged unloading buoy system, which will also act as the unloading system. The STL system is already in use for offloading crude oil in several developments worldwide, including the North Sea (e.g. Banff, Fulmar and Harding fields on the UKCS).

SPECIFICATIONS
Specific details of the size and capacity of the regas vessel;
Size 177,000 cubic metres
Tank type Moss 4
Length 300 metres (287 metres between perpendiculars)
Breadth 53 metres
Depth 28.5 metres
Draught 12.5 metres
POB 50
Supply vessels Two tugs during berthing, one supply vessels with tow capacities and one on location during offshore activities

The regas vessel will have sufficient thruster capacity to enable it to rotate around the buoy in a 'side by side' configuration and also retain full propulsion capability. The vessel will therefore have the capability to be operated as a ship at all times.

The regas vessel will have a safety certificate for 50 persons and 56 beds in total (excluding Hospital):

  • 35 cabins for crew;
  • 12 cabins for "passengers" (service personnel, owner’s representative etc.);
  • 3 cabins for cadets; and
  • 1 cabin for Suez Personnel with 6 beds (cannot be used for other purpose)

The vessel will be connected to the STL buoy for a 5 year service period, interrupted only by scheduled dry docks, which is expected to retain the ship classification. The regas vessel is capable of being readily disconnected from the STL and could therefore be unmoored from its location should an unanticipated event occur.

UNLOADING OPERATIONS
Once operational, LNG cargo will be pumped to the regas vessel via Ship-to-Ship Transfer (STS), re-gasified, and piped to the Port Meridian STL buoy system for entry into the NTS via the pipeline.

During operations, an LNG carrier will be moored in place using its own mooring equipment, with each mooring line being secured to a 'quick release' hook on the regas vessel.

When moored for ship-to-ship transfer, there will be a separation distance of 4.5 metres between the vessels - sufficient to fit a fender between the two vessels to avoid damage.

It is expected that each visiting LNGC will be moored on location between four and eight days depending on cargo size, buffer status and throughput rate. The vaporisation systems together with pipeline dimensions are rated for a maximum throughput capacity of up to 1,250 mmscfd.

SHIP-TO-SHIP TRANSFER
The LNG will be transferred from the arriving LNG vessel to the regas vessel through hoses or loading arms. Procedures for this transfer have been developed and it is considered proven technology.

The arriving LNG vessel will need to be fitted with connections for ship to ship transfer, but does not need to be fitted with vaporisation units or a receptacle for the STL buoy.

Both the regas vessel and the arriving LNGC vessel will, however, be fitted with equipment for ship-to ship transfer.

It is expected that, on average, LNG cargo will arrive once a week, with each visit lasting four to eight days. This would result in an expected maximum 52 ship-to-ship transfers per annum. In reality this number will vary, as during the summer there will be larger time lapses between visits as regasification rate is expected to be lower during these months.

Small scale STS operations have successfully been performed on 47 occasions by Hoegh LNG on the Norwegian west coast in the period from April to September 2007.