Technical Issues Associated with the Integration of LNG Production and Storage Facilities Using Floating Concrete Sub Structures

Abstract

Abstract Governments and Operators are researching the potential for the development of floating liquefied natural gas (LNG) production facilities as a means to monetize gas reserves and to eliminate flaring of natural gas associated with oil extraction. Floating Production Storage and Offtake (FPSO) vessel hulls may be constructed in either steel or concrete. Concrete hull structures offer a number of advantages for the support of cryogenic facilities and the storage of produced liquids. Additionally, concrete substructures may be constructed in country using a significant proportion of locally procured materials and labor. A concrete FPSO solution has been developed to support a two LNG train facility. The concrete hull may be configured to be much larger than traditional steel FPSO alternatives and need not limit the liquid storage volume or deck area. The proposed solution has sufficient deck area to allow the topside facilities to be configured with some modularization and preassembly using vendor supplied skids. Cryogenic liquid containment requirements have been reviewed for the offshore storage. It is concluded that "double" liquid containment should be adopted rather than the "partial double" containment typical of LNG carrier ships. The adoption of the double containment design criteria has implications for the alternate storage systems, membrane or prismatic self-supporting tanks. It is accepted that the membrane system can be shown to be double containment and is well suited to a concrete FPSO application. The prismatic self-supporting tankage system requires further development, but could also be used. Concrete hull vessels can be shown to be durable and stable. The proposed CFPSO arrangement has a wide beam that ensures superior stability and low motions in extreme environmental conditions. The proposed CFPSO construction could be carried out in country and has been shown to be feasible for several locations. Indicative costs are provided, which are competitive with other alternatives, especially on a life cycle evaluation. The 9MMTPA LNG production CFPSO may be completed within 43 months of EPIC contract signing. Introduction Governments and offshore oil and gas field operators are researching means by which natural gas from associated and stranded gas fields may be monetized. In addition, governments are legislating to limit or prohibit the flaring of gas associated with oil production. The result is an increasing interest in the development of offshore gas liquefaction installations, in particular the development of floating liquefied natural gas (LNG) production facilities. The primary focus of floating LNG proposals has beendirected toward steel hulled floating, production storage and offtake (FPSO) vessels. Steel hulled FPSOs may be procured from established shipyards and fitted out at an offshore fabrication and assembly facility. Established fabrication and assembly facilities are located in East Asia, Northern Europe and North America. Construction of the hull and topside facilities in a shipyard offers a number of benefits including contractor competition at bid stage. However, shipyards generally do not have the dock facilities to construct large concrete substructures. An alternative procurement strategy that incorporates local construction in purpose built graving docks is better suited to both the concrete substructure option and a procurement strategy that seeks to assemble the production facility locally..