Abstract

The first offshore LNG import terminal project that received approval from the US Coast Guard shortly after the Deepwater Port Act was amended is of the Gravity Base Structure (GBS) type. However, floating solutions are following closely in its footsteps with a first application recently approved for a Gulf of Mexico location, and with new Floating Storage and Regasification Units (FSRU) applications expected to be filed during this year for the west and east coast of the U.S.

Because the GBS and FSRU concepts are quite different, they are generally proposed by different industry sectors. Apart from a few exceptions, a civil contractor is generally not in the business of floating steel vessels and vice versa. Each of these industries likely has its own perceptions of so-called drawbacks of the concept proposed by the competition, while turning a blind eye to its own concept limitations.

This paper analyzes in which circumstances the FSRU, and in which the GBS would be the preferred solution, depending on project-specific conditions. This is done by means of a technical comparison, as well as a sensitivity analysis on the respective main cost-affecting parameters for both concepts.

The paper highlights how the FSRU and the GBS concepts differentiate themselves on issues such as environmental conditions, berthing, bat hymetry, constructability, operability, technology selection for storage, and regasification, etc.

The results of this study showed that the two concepts showed siginificant differences in sensitivity to project -specific conditions.

Background

There is a need for increased LNG transport to support the fast growing demand of LNG, especially in the USA. Until now only onshore import terminals have been built for receiving LNG, storage of LNG, regasification to natural gas (NG) and send -out of NG. Preferably these terminals are located close to densely populated areas, where the majority of consumers of this type of energy are found.

However, public opinion in several countries is getting more and more opposed against onshore LNG terminals, considering perceived safety risks and/or visual pollution of surroundings. Furthermore governmental issues like permits, environmental impact studies, etc. may significantly slow down the progress of new onshore LNG terminal projects.

Therefore the alternative of offshore LNG import terminals has been proposed. Such facilities should fulfill some important constraints:

  • They should be located practically out-of-sight from the coastline, in order to prevent public concern regarding safety and visual pollution of horizon (NIMBY)

  • They should have a high operability with regard to:

    • Berthing & offloading operations of LNG Carriers, which is dependent on environmental conditions

    • Processing of stored LNG to NG, which might be impacted by environmental conditions like seawater temperature or wave-induced vessel motions

    • Redundancy of systems (enabling maintenance and repair without decreased performance)

There are basically two fundamental concepts for offshore LNG terminals:
  • Floating: Floating Storage and Regasification Unit (FSRU)

  • On seabed: Gravity Base Structure (GBS)

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