Multiple development options are currently available for the production of LNG with the gas extracted from ultra-deepwater gas reservoirs. The main are (a) Subsea-to-Beach coupled with onshore LNG - with or without late-field-life gas compression; (b) Dry-tree/ Wet-tree Host coupled with onshore LNG; and (c) Floating LNG.Subsea-to-Beach and Dry-tree/ Wet-tree Hosts are field-proven options, within their own respective technological limits and financial applicability boundaries, and are being used for major capital projects. FLNG is now in the commercial phase with several worldwide projects under execution, and is becoming a more and more popular alternative development ‘building block’ to be adopted in some specific cases.

Several factors affect the decision on the ‘best’ development option for ultra-deepwater gas reservoirs. The readiness status of subsea technologies is one of these factors due to the fact that a subsea production system is required in all the development options discussed here, as well as location and features of the reservoir(s) to be produced, the recoverable reserves, and the size of the LNG train(s) and of the entire offshore and onshore facilities.

In the light of the increasingly wider interest of the industry in FLNG developments for offshore gas fields, it is worth creating simplified, yet reliable and robust, work methods to confidently discuss the Subsea-to-Beach and FLNG alternatives for a given project.

The present paper is a contribution to this discussion on Subsea-to-Beach versus FLNG, especially to the identification of the applicability limits for these development options.

Relevant Subsea-to-Beach and FLNG projects are selected and reviewed; the technological limits of the enabling subsea technologies are investigated; the key technical and decision factors in the Concept Selection are assessed and then discussed with respect to non-technical factors such as HSE, risks, economic viability and technology readiness status.

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