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GIFT
Gas import floating terminal

The project concerns the development of an offshore floating LNG (liquefied natural gas) storage and re-gasification terminal in which a large hull is moored to the seabed by means of a turret mooring system that allows the terminal to move freely around it in accordance with the prevailing weather conditions.

Tags: Water

Background

Today, the LNG industry is operating mainly inshore coastal terminals that lead to large onshore facilities, raising increasing safety concerns and traffic congestion issues.

New alternatives solutions are proposed:

  • offshore gravity base structure (GBS) terminals consist of a concrete or steel gravity structure, sitting directly on the seabed. It can integrate all the basic functions of an onshore LNG terminal (protected berth and unloading facilities, storage capacity for LNG, re-gasification unit, etc.)
  • a platform-based terminal does, which does not store LNG but is just used to provide a berth for the carriers and to support the facilities used to refill the LNG and export the natural gas onshore. It does not offer any protection for the carrier from wave and swell, and can only be used in sheltered areas
  • converted LNG carriers: this solution uses specialised LNG carriers equipped with a turret mooring system that can be disconnected and a conventional HP gas swivel connected to a flexible gas riser. The gas production is exported from the carrier via a PLEM (pipeline end manifold) and a sub-sea export gas line. The gas production is interrupted once the LNG carrier is discharged before the next one is connected.
  • FSRU (floating, storage, re-gasification unit) with turrets, is an offshore LNG receiving terminal which resembles a LNG carrier permanently moored at a given location. The mooring system is similar to the ones used for mooring FPSOs (floating production storage and off-loading). The concepts can move freely around a single point mooring system. The LNG carriers unload the LNG onto the FSRU using two techniques: side by side (in a benign environment), or in a tandem arrangement (the LNG export hose still has a technological gap).

Objectives

The objective of the project is to prove the feasibility of the concept and to increase knowledge on a specific innovative design of the LNG import terminal.

The hull and moorings are to be designed so that transverse thrusters are able to rotate the hull so that it is held almost transversely in the direction of the prevailing seas. In this way the hull acts like a breakwater and creates a calmer area in its lee in which the LNG carrier berths, discharges and unmoors safely.

When a LNG carrier is not alongside, the terminal moves freely, thus minimising the loads acting on the terminal and its mooring system in all weathers.

Therefore the challenge and the technological objectives of the GIFT project are to design a terminal, which:

  • can berth the LNG carriers side-by-side in an extended range of weather conditions
  • reduces relative movements of the terminal and the LNG-carrier so that the offloading operations are close to those traditionally used in sheltered coastal terminals, allowing for the existing cryogenic loading arm design to be used
  • is located at some distance off the coast in order to achieve safe, environmentally friendly, fast and efficient offloading operations, and to avoid traffic congestion and to respond effectively to safety concerns presently raised by the approach of increasing traffic of LNG-carriers to shore
  • is cost-effective, constructed and delivered in a shorter time than inshore terminals.

Description of work

The programme of work has the following objectives:

  • To define the position of concept with respect to other alternatives and to understand its value and attractions to the end customer. Potential end users of LNG terminals are attending design review meetings from the beginning of the project. Their contribution is of paramount importance, since they will give input, opinion and criticism throughout the design process. They have participated in the definition of the design criteria and functional specifications.
  • To carry out the necessary design work to validate the perceived advantages of the concept as outlined above.
  • To validate the design work by both hydrodynamic testing and by computer analyses.
  • To examine the structure and related systems in sufficient detail so that the unexpected issues resulting from innovation are covered and resolved.
  • To identify the way in which the structure could be fabricated, assembled, installed and operated in order to provide a cost-effective alternative to existing technologies. To generate the appropriate outline methods and cost evaluations to allow end users to examine these proposals.
  • To take the conceptual analysis and design to a point where there is sufficient technical and commercial development to allow a potential end user to have confidence that the concept can be included in comparative evaluation of alternative development scenarios.

Results

The project methodology is based on close co-operation between the participants, and the membership of the consortium carrying out this work bridges the marine offshore industries and covers the range of skill and capabilities required without duplication.

The project output will bring the concept from its present conceptual form to a state of maturity where it can be confidently considered by oil and gas companies for their future developments. It will have gained the confidence of the engineers, certification authority, builders and potential owners for future presentation to local authorities. The planned output and deliverables will give the concept sufficient maturity to be robust in evaluation by the operators and be in a state where it is sufficiently developed to be usable in the required time-scale.

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