Abstract

The Snøhvit project in the Barents Sea is a milestone in subsea oil and gas development, with a record breaking offset and all subsea facilities tied-back to shore.

The key elements of technology required to implement such a new development with a subsea Production Controls System qualified to operate over a distance of 220km are:

  • Long-range communications with no repeaters

  • Long-range supply of power at 3 kV

  • High data rate requirements

  • HV electrical and fibre-optic wet-mating connectors

  • A cost effective main umbilical

  • Diverse backup strategies

This paper will focus on the technical achievements in executing this ultra-long offset subsea-to-beach project which is now nearing completion.

  • The implementation of fibre-optic communications, subsea data routing, high voltage and power distribution technologies.

  • Back-up communications on Power "COPS" system

  • The Backup Intervention Control System (BUICS) designed for use in the event of main umbilical non-availability.

Snøhvit - Field & Project Background

The Snøhvit project in the Barents Sea is a milestone in offshore oil and gas development. It will be the first Norwegian and European production and export facility for liquefied natural gas (LNG). The field lies 140km from the coast of Northern Norway, and its production will be piped to a receiving and liquefaction plant on Melkøya island outside Hammerfest. This field is the first development in the environmentally sensitive Barents Sea. It is located at 71° 30' north, within the Arctic Circle and 1,000km north of the Norne field, currently the most northerly producing field offshore Norway.

After processing and liquefaction, LNG will be shipped in special carriers to markets in Spain and the USA. Approximately 70 consignments are due to be exported annually over the field life of almost 30 years.

Snøhvit is the first Norwegian offshore development with no surface-piercing installations on the field. The pipeline carrying production from the subsea installations to Melkøya is 145km long is a world record distance for piping an unprocessed wellstream. The associated subsea control system that has now been installed is a world record for long-distance tie-back. In addition, the control system is designed to support the future Askeladd development where the total offset will be 178km. All technology has been qualified to 220Km.

It has taken time for the technology to be developed such that the field becomes feasible. The primary technology gaps that had to be closed were the long offset control and compact, efficient LNG plant, together with long offset multiphase flow. In combination these technologies allow subsea development without the need for a conventional surface structure.

The first gas discovery was made in 1981, and the blocks containing the three discoveries were awarded in 1984 and 1985. A total of 16 exploration wells have been drilled in the area. In May 2002, Statoil obtained approval from the Norwegian Government to develop the field. By the 12th June, Construction work had started on Melkøya with first production scheduled for summer 2007.

The subsea development envisages some 21 production wells and a carbon dioxide disposal well. This disposal well represents a large contributor to a much-reduced environmental impact from the development (700,000 tonnes of CO2 from the reservoir is re-injected each year). The focus on environmental impact is, of course, due to the environmentally sensitive nature of the area and also that it is an important fisheries area.

Clearly the use of a subsea development with remote control from shore is a cost-effective solution that contributes to ensuring safe shipping routes and in line with Norwegian practice; the subsea templates are designed to be over-trawlable and the pipeline routes are also chosen so as to reduce their possible hindrance to fisheries.

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