Large quantities of gas are associated with the development of offshore oil and gas fields and companies are faced with many challenges in handling these gas reserves. In deepwater remote areas there is generally no existing infrastructure to allow the gas to be sent to the market and many host countries are requiring companies not to flare gas. Some countries have built large facilities to turn the gas into LNG; for example, Nigeria, Algeria, Indonesia and Qatar, and these facilities have been based on large base loads. Typical LNG train sizes have been in the range of 3.0 million tonnes a year with a minimum entry-level production rate being 0.5 BCF/Day or higher. This threshold is too high for offshore oil fields with a more typical peak production of 100,000 to 300,000 BPD of oil and up to 250 MMSCFD of produced gas.
A concept has been developed for the exploitation of associated and stranded gas resources using a Floating LNG facility that can be moored in deepwater next to an oil production facility. The system is based on a patented turbo expander process that was developed by ABB Randall Gas Technology to liquefy natural gas streams and is called NicheLNGSM. The system uses no intermediate liquids for cooling and has a very low equipment count. This Floating LNG system is based on the storage of product in a vessel similar to a typical LNG tanker with the NicheLNG process located on the deck. Gas streams can be either preconditioned, i.e., NGLs removed, dehydrated, and contaminants removed or these operations can be done on the Floating LNG.
This Floating LNG system is viable for development of stranded gas in the 0.5 to 3.0 TCF range with production rates from 75 to 300 MMSCFD. This paper will detail the work done by ABB in the development of the Floating NicheLNG vessel. The principle focus of the paper will be on the marine aspects of this development including selection of containment system, mooring and offloading concepts. Global performance analysis was used to establish criteria for the topside design and to determine loadings for off-take. A description of the liquefaction process is included. The results of the risk assessment carried out covering the overall scheme will be included.