Abstract

With large ‘stranded gas’ reserves in remote locations, a number of developments are assessing the feasibility of large scale offshore LNG production. However, the processing facilities, ‘footprint’ is substantially beyond the scale of any offshore production facilities to date.

A ‘Mega Jack-up’ based on Technip's TPG 500 production jack-ups is described in this paper. It is a Heavy Production Platform (TPG 500 HPP) developed by Technip and capable of operating in shallow water (typically up to 60 m / 200 ft) located in harsh environmental areas of the world (e.g. cyclonic), therefore requiring deck installation with a high air gap.

The ‘TPG 500 HPP’ is designed to transport and self-install as a single element an LNG plant with a dry weight of circa 120 000 tonne laid out on an area of 36 000 m2. The concept is predicated on:

  • The advantage of minimum offshore hook-up, the complete system being integrated and commissioned at-shore, coupled with a fast installation.

  • A solution without major soil preparation and minimal seabed environmental impact (compared to a " sunken?? concrete barge or GBS).

The concept is a development of establish production jack-up technology: it is transported in a wet tow configuration to the offshore site, the legs jacked down to transfer the load to the leg foundations and the deck elevated to its final air gap, where it is locked in place, all within a matter of hours.

The concept consists of a jack-up with up to 18 independent legs and associated load distribution system resting on conventional spud can foundations. Therefore, it does not require any dredging or specific soil preparation to compensate for soil heterogeneity and/or bathymetry variation. The ability to vary the elevation of the HPP during the life of the field also provides a safe solution in the case of soil settlement beyond that originally designed for.

The developed construction strategy is based on modularised topside facilities from multiple fabrication sites and offers various scenarios for installation and module integration depending on availability of a dry dock or quay facility.

The ‘Mega Jack-up’ greatly extends the geographical range/water depth for a HPP installation and offers a cost effective alternative to relying on multiple platforms (and their associated requirements for installation vessels) or a ‘sunken’ concrete barge.

Introduction

Historically, the offshore industry has considered offshore production of LNG by focusing on 1 to 3 million tonne per annum (MMTPA) sized units with basically two fundamental concepts for the substructure:

  • Floating: Floating Production Storage and Offloading (FPSO)

  • On seabed: ‘Sunk’ concrete barge, or gravity base structure (GBS)

However, today, the LNG liquefaction industry is looking for high capacity units of 5 to 8 MMTPA and these require a processing footprint that is well beyond the scale of existing FPSOs i.e. a floating system is space limiting if wanting to develop such a large facility offshore.

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