With the LNG market booming, the need for a reliable and safe means of transferring LNG from a producing floating facility to an LNG carrier and from this carrier to a near-shore terminal is becoming acute. In this context, the SYMO® (Soft Yoke Mooring and Offloading) system has been developed and recently tested in MARIN's offshore basin. Important lessons have been learnt from these model tests and from the calibration of numerical tools performed thereafter. One of the main issues is the inherently weakly damped nature of a moored LNG carrier. Consequences in terms of system design, mooring analysis methodology and model test program will be discussed. Another issue specific to nearshore import terminals is the shallow water effects on the wave drift forces. These effects will be discussed and guidance regarding their importance will be provided. The paper will also address the evolution of the concept based on the model test findings. In particular, the thorough design work performed with a view to obtaining an Approval in Principle (AiP) from one of the leading classification societies will be discussed with emphasis on the HAZID conclusions. Introduction Prompted by a strong demand in energy from both developed and developing countries, by tougher environmental constraints related to flaring as well as by safety issues (NIMBY), the fast growing LNG market has stimulated the industry into finding a number of innovative ways for LNG transfer. The aim is to transfer the LNG between near-shore or offshore fixed or floating structures and LNG carriers. Central to all these transfer systems is the standard 135,000m3 capacity LNG carrier with its distinctive hull shape designed to achieve cruising speed up to 20 knots and its almost constant draft whether laden or empty. Firstly a brief description of an innovative solution for LNG transfer will be given before covering in some detail the model tests performed in 2003. These tests were conducted to assess the feasibility of the concept from three viewpoints: connection, offloading and disconnection. Next will follow a detailed discussion of the calibration of numerical tools against model tests emphasizing the issue of damping, the shallow water effects on wave drift forces and the ability of numerical tools to capture the physics and therefore match the test results. Lastly will be briefly discussed the Approval in Principle sought from a leading Classification Society and its recommendations, especially those related to shallow water. Conclusions will be drawn as to where more efforts should be directed to in the near future. SYMO Concept Description In general terms, the SYMO system has been designed to provide a disconnectable mooring of an LNG carrier to a fixed or floating structure in a harsh offshore environment and to ensure a safe and reliable offloading of LNG at industry standard transfer rates with maintainable service and minimum downtime. The SYMO concept consists of the following main components (see Figure 1):A: JacketB: Revolving craneC: Mooring legsD: Yoke A-frameE: Yoke noseF: Upper connectorG: Lower connectorH: Fluid transfer piping
Liquefied Natural Gas (LNG) trades are expected to increase rapidly over the coming years and the gas industry is preparing itself by planning facilities for import and export of LNG. In the USA alone, dozens of prospective import sites have been identified of which many are planned offshore due to security concerns and public opposition against onshore facilities.Amongst the terminal concepts developed and promoted, floating terminals attract the attention of the industry, offering the combination of use of proven technology with attractive cost and schedule.A key issue for any offshore LNG import terminal is the safe and reliable transfer of LNG from LNG Carriers (LNGCs) to the terminal with sufficient availability. For floating terminals such transfer is typically performed in a side-by-side mooring arrangement.The safety and availability of the offshore LNG offloading operation is governed by many elements, including the performance of the assisting tugs, the general sea state conditions, the mooring line and fender arrangement, the loading arm design and its operational envelope, emergency conditions, LNGC maneuverability, but also tugboat and mooring master competency and the amount of specialist training.This paper addresses how SBM -the company with the world's longest track record in offshore offloading of hydrocarbons, and operating the largest fleet of floating production systems in the world -has combined results from numerical analyses and model tests with feedback from marine operational practice to define how offshore LNG transfer can be done safely and with sufficient uptime.The paper will present a step-by-step insight into the offloading operations supported by practical examples of sideby-side offloading operations from the world's largest LPG FPSO, and give typical availability figures for side-by-side LNG offloading for various locations in the world. In addition, alternative offshore LNG offloading solutions will be discussed for those locations where higher uptime will be required.
With the present deepwater developments on the increase it is foreseen that adedicated market will develop for vessels capable of intervening on subseawells at a lesser cost than existing deepwater drilling units. Thereby (I)extend the life of deepwater developments rendering additional profits and (II)adhere to minimum field production requirements as are being required by theauthorities more and more to date. The paper describes the development of the concept for such a Well InterventionVessel resulting from a combined effort between a Naval Architecture DesignBureau and a major rig equipment supplier with a focus on an open equipmentstructure facilitating the possible application of multiple levels of/andintervention solutions. The vessel will target Class B+/(II+) and Class C/(III)type interventions, based upon systems which will use risers and capable ofretrieving completions. Input of operators as well as equipment- and serviceproviders has been used in the development of the concept to develop the opensystem. The proposed paper shall present in detail the design approach and basis, theconcept design and the operational parameters of the deepwater well completionand intervention vessel. It will also address in detail the specific pieces ofequipment to be used on the vessel.
Today hard riser, dry tree systems not carried on a bottom founded structure are supported by either a TLP or Spar. Both of these systems directly or indirectly use buoyancy to achieve the riser tensioning. The use of buoyancy requires that the relative motions of the buoyancy and the risers be kept small. The TLP does this by tendon restraining the buoyancy, while the Spar does this by creating a somewhat quiescent water shaft in which buoys can effect a relatively uniform riser tension. The physics of an FPSO require that the tensioning system cope with draft changes and larger relative motions between riser and floater. A weight-based riser tensioning system has been developed and tested which is able to cope with both the large stroke and relative motions required to make hard risers practical for FPSO systems.
The attractiveness of placing a natural gas liquefaction plant on a vessel moored at or close to an offshore field is known. This vessel can either be part of an oil development in which it liquefies associated gas or a stand alone development of a gas field. In the associated gas case, the Floating LNG (FLNG) unit makes certain oil developments feasible by turning the associated gas disposal into a moneymaking opportunity. In the gas field case, the FLNG makes remote offshore field production economic. The safe reliable transfer of this LNG in open sea, possibly harsh, environment has however not been possible. The proposed LNG Offloading Arm (LOA) effectively combines proven technology and operating experience to effect the safe and reliable transfer of LNG between tandem moored vessels or between a fixed tower and LNG carrier in up to 5 meter significant seas. The concept is based on the experience of mooring systems surviving 100 years storms, dis-connectable mooring systems in typhoon areas and work performed on cryogenic swivels. The LOA structure consists of "vertical" and "horizontal" arm section with swivels to provide articulations required to follow the relative motions between the FLNG and the tandem moored LNG carrier. The vertical section is supported from a cantilevered rotating structure on the back of the FLNG vessel or on a fixed tower. The horizontal section connects the LNG carrier to the lower end of the vertical section. Each section is composed of a central pipe for LNG transfer and a large diameter outer pipe structure also used as the vapor return from the LNG carrier. The LNG carrier can be passivelymoored using gravity restoration by weights located in the horizontal section of the loading arm or DP assisted using both the arm and the LNG carrier thruster system. Introduction The technology for cryogenic liquefaction and storage of LNG on an offshore floating vessel is known. The safe reliable ship to ship transfer of this LNG in an open sea, possibly harsh, environment has however not been possible. SBM having experience in both the supply and operation of mooring systems put this experience to work in the development of a Tandem LNG Offloading system. The philosophy adopted for this development was to keep the design simple and whenever possible stick to components that had a known track record. Having over 40 years experience in the design, supply, and operation of Single Point Mooring (SPM) systems and Floating Production Storage and Offloading (FPSO) systems the value of simple robust design was well understood and applied to this LNG Arm development. Known technology and operational experience either directly or indirectly applied to the Arm include soft yoke or gravity moorings (Fig. l), articulated fluid transfer arms (Fig. 2), cryogenic swivels (Fig. 3a and b) and tandem mooring systems (Fig. 4).
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