Powering ahead on the NCS

15.12.2010
Big plans for supplying Norwegian offshore platforms with power from shore were under study a decade ago. Some are now being realised, while a number of others continue to be investigated.
  • Bjørn Rasen

Photo: BP

Electric.
BP’s converter station at Lista is linked to the Nordic power grid. From here, the transmission cable runs to Valhall in the North Sea. (Photo: BP)

 

The Storting (parliament) resolved as early as 1996 that power from shore should be explored by developers and followed up by the government for each new project on the NCS.

Some have argued that all Norway’s offshore installations should change their energy supply from local gas turbines to land-generated electricity transmitted by cable.

Although gas turbines represent the biggest component in total Norwegian carbon emissions, however, many such projects would have a limited impact on reducing the amounts being released.

This is because declining output on many of Norway’s biggest fields means there would be little point in spending heavily on measures with only a few years to run before production ceases.

Another problem is that converting existing platforms to take the transformer modules required for power from shore could be costly. Space and weight constraints also create complications.

But studies by the NPD and others show that power from shore represents a realistic option for new developments and major conversion projects on existing facilities.

Opportunities for the coordinated supply of power from shore to the Ekofisk, Eldfisk and Ula fields are accordingly now under consideration, with findings due by the end of the year.

 

Photo: BP

Ashore.
The transmission cable from Valhall is pulled ashore at BP’s Lista converter station at Norway’s southern tip. (Photo: BP)

 

Technical

This work is being pursued by operators ConocoPhillips and BP with a view to identifying the technical feasibility and cost of a possible coordination.

The NPD has asked the two companies to carry out this study in connection with plans for major conversion projects and new installations in the Ekofisk area.

BP is also planning to replace the power supply on Ula within the next few years. This field as well as Ekofisk and Eldfisk are expected to remain on stream for a long time.

“We’re fully confident that the operators are making the necessary investigations,” says Johannes Kjøde, the NPD’s director for discoveries and fields in the southern area.

“This will allow power from shore to be viewed as a genuine option for these fields when the companies present their development plans for government approval. The cost of such measures must be assessed when the studies have been completed.”

 

Commercial

Power from shore is certainly a possible solution in commercial terms, as demonstrated by one of the oldest producing fields on the NCS.

Valhall, at the southernmost end of Norway’s North Sea sector, is being provided with a new field centre to replace its oldest platforms.

All the pieces have fallen into place here, so BP will be operating the field from 2011 as the first on the NCS with full power from shore.

Designated by BP for various reasons as one of its fields of the future, Valhall will be supplied from the Nordic grid via a dedicated converter in Lista at Norway’s southernmost tip.

Delivering electricity via a transmission cable from land is not a new idea for either BP or Ekofisk operator ConocoPhillips, reports Sverre Gilje.

A retired BP employee now working as a consultant for the company, he has been working on such concepts for more than a decade.

“We had big visions in 2000,” Mr Gilje recalls. “A team drawn from BP in Britain and Norway explored the prospects for power from shore throughout the North Sea.

“In addition to contacting many of the operators in Britain and Norway in this connection, we collaborated with Norwegian grid operator Statnett and the National Grid in the UK.”

The idea was to run a cable from the hydropower station at Suldal near Stavanger via Karmøy to BP’s 2/4 G platform on Ekofisk, which would serve as a hub.

This transmission line would continue to Britain’s Forties, acting as a second hub, and then on to Peterhead in north-east Scotland.

“The interest was there, but the players had varying positions,” says Mr Gilje. “Fields were at different stages of maturity, for instance. We ended up with the Norway Power Project, with BP in the driving seat and Statnett also involved.”

The latter scheme came to an end in 2002, when Norwegian electricity prices were high and locally generated power was in short supply.

 

Platform

Sverre GiljeMr Power-from-shore. Sverre Gilje. (Photo: Emile Ashley)

New studies were launched by Mr Gilje and colleague Asbjørn Tansø with the main focus on supplying Valhall, where a new process and quarters platform was planned. The solution was a 78-megawatt power cable running for 300 kilometres from Lista.

“Cutting operation and maintenance costs is one of the keys to an estimated 40 years of remaining production life for Valhall,” Mr Gilje notes. “Power from shore makes that easier to achieve.”

BP and its partners decided in May 2005 to adopt this approach in their plan for development and operation (PDO) of the field, which was approved by the Storting during the summer of 2007.

The solution was due for testing in October, and gas turbines will be replaced by a silent electrical transformer when the new Valhall installations become operational in 2010-11.

This unit will convert direct current from land into alternating current for the whole field. Mr Gilje reports that the field will only have three small six-MW emergency generators to let people stay aboard until the main supply is restored.

“However, we regard the system as reliable. It’s well-known technology, of course, but never applied offshore before. This will be something new for the operators, who’ll have to run it as a high-voltage facility.”

BP is now pursuing a new study together with ConocoPhillips concerning opportunities to supply the latter’s new Ekofisk installations as well as Ula with power from shore in 2014-15.

The gas turbines on Ula are under consideration for replacement in 2014-15, but it might be possible to extend their economic life.

Should an internal assessment due to be completed by 30 September conclude that such an extension is possible, the power-from-shore study could be postponed.