Operability of a floating LNG production facility

Abstract

The advantages of offshore floating liquefied natural gas (FLNG) production include reduced environmental footprints and potential reduced costs for remote and marginal field development. Moving a conventional land-based LNG plant offshore, however, does not come without its fair share of challenges. Ensuring operability—and hence availability—is one of those challenges.

While offshore natural gas process technology selection is largely dictated by limited deck space and high safety focus, a crucial aspect in the design and operation of any of the equipment onboard an FLNG facility is the motion characteristics of the hull in the metocean environment. In fact, hull motions affect the performance of the LNG storage tanks, cargo offloading systems, module structural connections, and nearly every single piece of topsides equipment.

Determining the required performance of the hull, however, involves an iterative process between the design of topsides equipment and the configuration of the hull. On one hand, the hull is optimised to minimise its responses to the operating environment and to best suit any operational limitations of process systems and equipment. On the other hand, the process systems and equipment are modified to perform under greater hull motions.

The cryogenic transfer of LNG between an offshore floating production facility and its designated LNG carriers is one of the weakest links in the total chain of offshore floating LNG development. It involves two floating systems, working in close proximity, in the dynamic offshore environment. The operability of this greatly affects the availability for LNG offloading and overall delivery.

The purpose of this paper is to review the operability aspects of an FLNG project, particularly those affected by hull motions. State-of-the-art operability design and assessment methods will be discussed, including outcomes of some of the dedicated research and development programs that have made FLNG a foreseeable reality for Australian and worldwide offshore natural gas projects and prospects.