Offshore LNG Transfer: A Worldwide Review of Offloading Availability

Abstract

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.

Time Domain Simulations of Side-by-Side Moored Vessels: Lessons Learnt From a Benchmark Test

“…For the cryogenic offloading arms, an operating envelope of typically 2 m can be assumed, based on presently available technology. More details regarding downtime analyses can be found in Poldervaart (2006) and Grin (2005).…”

“…The higher limits predicted with our calculations can be explained by the use of the longer (25 m) nylon tails and additional safety margins used in real operations. Furthermore, it must be borne in mind that the actual offloading is only one of many stages of the whole berthing and offloading operation, between LNGC arrival within a mile from the FSRU and its sail away, see Poldervaart (2006).…”

“…6 shows comparison of relative surge, sway and yaw motions. Relative motions are computed as LNGC motions minus FSRU motions.…”