OIL has started to flow from an oilfield east of Shetland – a flagship development seen as one of the most complex in the North Sea.

The Mariner field, one of the country’s biggest, is expected to produce more than 300 million barrels of oil over the next 30 years.

Equinor, its Norwegian operator, said the development will support more than 700 long-term jobs and generate significant revenue in the supply chain for decades to come.

The Norwegian energy giant said contracts worth more than £1 billion have been awarded to UK suppliers since work started and 1500 people were involved in the hookup and commissioning of the development.

Mariner is expected to produce annual average rates of around 55,000 barrels of oil per day and up to 70,000 barrels per day at peak production.

Anders Opedal, Equinor’s executive vice-president for technology, projects and drilling, said: “By gathering and interpreting new seismic data we have improved our understanding of the reservoirs.

“This has resulted in fewer and better-placed wells and increased resources since the project was sanctioned in 2012.

“With the significant volumes in place, we see clear potential to further increase the oil recovery from the Mariner field and will proactively seek opportunities to do so through the application of new technology, additional drilling and future tie-back opportunities.

“With the start-up of Mariner, we have delivered one of the most complex developments in the North Sea and Equinor’s portfolio.

“We will continue to apply digital solutions and new technology to deliver safe and efficient operations and optimize production.”

Mariner has come on stream after a £6.4bn investment – one of the industry’s biggest in the past decade.

The field is located on the East Shetland Platform of the UK North Sea, around 95 miles east of Shetland and 198 miles north-east of Aberdeen. It was discovered in 1981, but the industry did not have the technology then to make it viable.

It took decades for technology to advance sufficiently to develop it, and Equinor submitted a development plan in 2012.

The field has two reservoirs, and almost 100 wells are expected to be drilled over the next 14 years.

It is also expected to be the last major North Sea infrastructure project until Shell’s Penguins field redevelopment starts in 2022. Equinor is using the latest in digital technologies, automated drilling and a digital copy of the platform to make it safer and more efficient.

Marine production should have started last year, but “challenging” weather and a series of contractors’ stoppages in December pushed the date back.

Equinor is the operator with 65.11% equity, and its partners are JX Nippon (20%), Siccar Point (8.89%) and ONE-Dyas (6%).

Hedda Felin, Equinor’s senior vice-president UK & Ireland offshore, said: “This start-up of the Mariner field is a huge, significant milestone for us.

“It is Equinor’s first UK operatorship. It is the largest investment in the UK Continental Shelf for the last 10-15 years, and it is the second operatorship offshore that Equinor has outside of Norway, so there is a lot of focus from all angles.

“We have been working on the project for a long time.

“We have had some delays, but then we’ve tried to use that time in an optimal way to be robust in order to have a safe start-up.”

Felin added: “It is a big milestone for a lot of people. Many companies have been involved, so we’re very grateful to all of them that we are now at this stage of starting up.”