BP has held out the prospect it might sanction further massive investment off Shetland although other oil and gas giants are facing complications in the area.

Dave Lynch, a key member of BP's North Sea management team, has highlighted the possibility the oil and gas major may proceed with a third phase of the huge Clair field west of Shetland in a move that would involve hundreds of millions pounds spending.

The £4.5 billion Clair Ridge development 50 miles off Shetland is one of two flagship schemes BP committed to with partners in 2011. First oil is expected in 2015.

BP also sanctioned a £3bn revamp of the Schiehallion and Loyal fields, around 110 miles from Shetland, with partners.

The projects are part of a wider surge of investment by oil and gas firms off Shetland.

France's Total is working on a £2.5bn project to bring the giant Laggan Tormore development west of Shetland onstream.

With all these fields expected to be in production for years, the Shetland area is firmly on the industry map after years of limited activity.

But some may be concerned by signs the newfound enthusiasm for the area may have already started to wane.

In November, Chevron, the US oil giant, dropped a bombshell when it said the planned £6bn Rosebank development, 80 miles west of the islands, was not currently economically attractive.

"Chevron's view is that the project does not currently offer an economic value proposition that justifies proceeding with an investment of this magnitude," it said.

Announcing the start of design work on the field in July last year, the company said:"The Rosebank project is another important step forward in our strategy to grow profitably in core areas of our upstream business."

The company has said it is still in the design phase of the project but not how long that might last.

Also in November, Statoil delayed work on the giant Bressay field off Shetland to simplify the scheme and to reduce costs.

Royal Dutch Shell, which has significant interests in Clair Ridge and Schiehallion, has a stake in Bressay. Asked if BP's enthusiasm had cooled since the company committed to the Clair Ridge and Schiehallion projects, BP's Mr Lynch said: "No. Point forward, we've got three areas we worry about: Central North Sea, Norway and West of Shetland, or Shetland as we call it. In five years' time, Shetland will be the biggest producer of the three groups, so it's really important to us, definitely."

The company has been making good progress on Clair Ridge. The giant legs or jackets that will support the production facilities were installed August.

BP is already working on what will come after Clair Ridge.

"We're working on the third phase of Clair. We're on the third well of a six-well programme and that's going fine," said Mr Lynch.

He added: "The appraisal programme we've got around Clair with our partners is £300 million just to invest in trying to understand what's down there - that's a big commitment."

Mr Lynch confirmed if all goes well there could be a third phase of Clair, which could "easily" involve a capital investment of several hundred million pounds.

Signalling confidence, the company has been accumulating exploration acreage off Shetland in recent licensing rounds.

"There's more finds to be made and there's more to be exploited from the existing fields," said Mr Lynch. He noted BP's acreage includes the undeveloped Suilven and Alligin discoveries.

Given the challenges involved in operating in stormy waters in an area in which there is not much in the way of production facilities in place, it is no surprise operators let a number of finds lie undeveloped for years.

Clair was discovered in 1977 but the first phase did not come onstream until 2005.

BP is benefiting from advances in technology that have played a key role in boosting the appeal of the area for oil and gas firms.

Advances in seismic imaging mean firms can get a much clearer picture of what lies beneath the ground than were imaginable when exploration work started off Shetland in the 1970s.

"We've now got technology that gives us Blu Ray definition," said Mr Lynch, who is VP Reservoir Development.

BP has just spent three years acquiring fresh seismic images covering all its Shetland assets, a task Mr Lynch said involved a huge effort and "massive investment".

Advances in drilling technology mean firms now have a greater chance of making finds and of producing oil and gas from them in commercial quantities.

Horizontal drilling, which involves boring deep down into the earth and then sideways, allow firms to penetrate multiple pockets of oil and gas with one well. Traditional vertical wells may offer fewer chances of success.

BP has had to overcome huge challenges to develop production facilities capable of withstanding the stormy conditions off Shetland, which Mr Lynch described as among the toughest in the world.

For Schiehallion, BP developed a system which involves a floating production storage and offloading vessel "weathervaning" with the wind around a fixed turret.

The company has laid pipelines that allow it to ship gas produced west of Shetland for which there is no market to the Magnus field north east of the islands, where it is pumped into the reservoir to help squeeze out more oil.

Noting that firms may only extract 25% of the oil and gas contained in fields in some cases, Mr Lynch said BP had invested heavily in developing techniques to boost recovery rates. Clair Ridge will employ a low salt content water to help drive oil from the rocks that was developed in Alaska.

The high oil prices seen in recent years have helped make Shetland more attractive.

But asked what it would mean if the economy tanked and oil prices tumbled to $80 from around $105 currently, Mr Lynch said: "Our fields will be okay.

"We're locked into contracts now that were locked in a while ago. Our planning price isn't a hundred bucks a barrel... so we're pretty secure."

Shell's finance chief Simon Henry said recently that he expected Clair Ridge and Schiehallion to be quite important parts of its portfolio for a "very long time to come".

Tax breaks for deep water developments have encouraged others to invest off Shetland.

In November, Enquest sanctioned plans for the £4bn development of the Kraken field east of Shetland, which will benefit from a relief that was introduced to encourage investment in heavy oil fields.

Statoil has said the delay on Bressay has no implications for the $7bn plan to bring the Mariner heavy oil field off Shetland into production.

For all his confidence in BP, Mr Lynch said collaboration between oil and gas firms will be key to maximising the potential of Shetland.

He noted the geology of the area is more difficult than in much of the North Sea.

But with independents like Faroe Petroleum exploring alongside the majors off Shetland, there seems to be little chance of the area become a backwater again any time soon.