Shell World Online

Harnessing the energy of a Viking long ship

Seldom has a gas field so far offshore been developed solely with undersea installations. New technology has enabled Ormen Lange engineers to construct their installations among the jagged, precipitous canyons deep beneath the waves.

by KIM BYE BRUUN
December 14, 2007

It was a celebration more typical of NASA scientists congratulating themselves on a successful space mission. When the news came down the phone line to their office in southern Norway, geologists turned and hugged one another. An exploration drilling team had been at work 120 kilometres (75 miles) off the Norwegian coast in an area where geological surveys had indicated the presence of oil and gas. On the drilling ship they were now examining samples from a layer of sandstone deep below the ocean floor, itself over 1,000 metres (3,280 feet) beneath the surface of a hostile sea. With such explorations often ending in disappointment, everyone had been prepared for failure. But as the test results came down the line the geologists knew they had succeeded in finding a vast new reservoir of natural gas.

When the joy subsided, the reality set in. For one thing, the industry had no experience of producing natural gas from deep water in such a harsh environment. For another, with Norway having no need of the gas, the closest likely customers were 1,200 kilometres (745 miles) away – and no undersea gas pipeline that long had ever been built. Then there was the unusually rugged seabed terrain, with powerful currents flowing amid deep valleys and towering hills. The icy temperatures on the seabed would pose another problem.

The challenges were daunting. Yet the determination to overcome them was driven by an even greater challenge: with easy-to-access oil and gas ever harder to find, how to meet the world’s increasing demands for energy? The need to explore in frontier locations – whatever the technology challenges thrown up – continues to grow. And at a time when concern over greenhouse gas emissions is rising, the newly discovered gas field in the Norwegian Sea – at 400 square kilometres (154 square miles) one of the world’s biggest offshore gas fields – offered the opportunity to develop huge reserves of the cleanest-burning fossil fuel.

Ten years and billions of dollars of investment on from that moment of joy for the geologists, the Ormen Lange field has started to yield its gas. It took persistence, tremendous resources and a series of technological triumphs to overcome the special challenges posed by the field, which bears the name of a Viking long ship meaning Long Serpent. The extraordinary effort necessary to harness Ormen Lange’s energy is likely to become more commonplace as the industry opens new frontiers in search of large, untapped sources of oil and gas. “In times of growing concerns over energy security, projects of magnitude and complexity such as Ormen Lange will become increasingly important if we are to meet the world’s rising energy demands,” said Fatih Birol, chief economist of the International Energy Agency.

Remote-controlled submarines

Finding the new field was only the start. A number of challenges confronted the companies that planned to develop it. To make it pay they had to find a cost-effective way of getting the gas up from such depths. The often-stormy weather conditions, coupled with the dramatically uneven seabed, would make installing production equipment a hazardous and logistically complex affair. And in this sub-Arctic region the cold at the bottom of the sea meant they had to devise a way of preventing the gas from freezing. Finally, getting the gas to the customers would involve building the world’s longest undersea gas pipeline.

Ormen Lange lies between 850-1,100 metres (2,788-3,609 feet) beneath churning waves that often hit 15 metres (50 feet) high. Its rich resources are locked nearly 2,000 metres (around 6,500 feet) beneath the seabed. Joint developers Shell and Norwegian energy firm StatoilHydro decided that building a platform would be too costly and posed safety risks because of the rough conditions. Instead they opted to use remote-controlled submarines to build installations on the seabed. This would remove the risks of having to man a platform and ferry workers back and forth by helicopter. Fitted with camera, sonar and two robot-like arms that can lift heavy weights of 100 kilograms (220 pounds) each, the subs use a range of tools to assemble and maintain equipment at depths where no diver could survive.

Yet using such technology presented its own challenges: when construction work began in late 2005, it was the first time these subs had been used in such a hostile environment. The below-freezing temperatures, the rough terrain and the forceful currents – some of the world’s strongest – meant that their performance could not be predicted with certainty.

Using information gathered by radio waves from the submarines, engineers drew up a detailed three-dimensional map of the sea floor that showed the steep inclines and deep gorges in the seabed where the production equipment and pipeline had to be laid. A giant crane on board a ship lowered three already-assembled steel structures, each weighing 1,200 tonnes, into place on the seabed in an operation that required remarkable precision. It took several weeks for the sea to be calm enough to go ahead, and the vessel’s crew had only one chance to get it right: once the structure’s foundations have sunk into the seabed, it cannot be retrieved.

The submarines – operated from a control centre on board a vessel above – then connected the pipeline to the installations, which contain sensors and valves that control the flow of gas and act as a safety mechanism. Engineers control the installations from an onshore gas processing plant through fibre-optic cables laid in the sea floor.

Longest pipeline

Although Ormen Lange lies off the coast of Norway, the Norwegians have little use for its gas: they have managed well for a century with domestically-generated hydropower. The nearest customer was the UK. Later, other countries in north-west Europe will be able to take the gas via another pipeline. To get the gas to the UK meant building and laying the world’s longest undersea pipeline, first to take the gas to the processing plant at Nyhamna on the Norwegian coast, and then beneath the North Sea to the UK’s Easington plant.

Nearly 100,000 sections of steel pipeline weighing a million tonnes in total were welded together in stages on two pipe-laying vessels, before being laid on the sea floor at the rate of 4 kilometres (2.5 miles) a day. The pipeline sections were coated in concrete and asphalt to protect against corrosion and to weigh them down on the seabed. To level out some of the more dramatic variations in the seabed peaks and valleys, some five million tonnes of rock were lowered along the pipeline’s course. Car-sized remote-controlled diggers with four spider-like legs excavated parts of the seabed to level it out further.

In the control room on board a support vessel, operators used a three-dimensional virtual reality model of seabed and machine to direct the diggers with absolute precision through near-zero visibility. Towards the Norwegian shore the sea floor rises sharply in a 30-degree incline – as steep as the slope of an Olympic ski jump, and the result of a massive undersea landslide more than 8,000 years ago. Here engineers faced a particularly tough challenge in lowering rocks into place and excavating the seabed.

At the greatest depths in Ormen Lange the temperature on the seabed can be as low as minus 1.2 degrees Celsius (less than 30 degrees Fahrenheit). This poses the risk that hydrates – a form of hydrocarbon ice – may form in the unprocessed gas as it flows through the pipeline, causing blockages that halt production. To combat this a glycol-based liquid is injected into the gas as it comes up from the well. The anti-freeze is separated out again on land and returned to the system.

Stretching the limits

Overcoming Ormen Lange’s many hurdles made the project an unprecedented challenge. A report by energy analysts Wood Mackenzie said the development- had “stretched the limits of technology”. It called the project a prime example of how to tackle such a hostile and isolated environment, and said it would serve as a model for the development of large frontier discoveries in the future. “Given the harsh environment, Ormen Lange is a spectacular achievement,” said the firm’s senior analyst for Europe, Andrew Slessor.

Shell, with a 17.04% interest, took over as production operator of Ormen Lange on December 1. Other partners are Petoro, StatoilHydro, Dong Energy and ExxonMobil. Three wells began producing gas in September, and more than 20 more wells are planned. They are the largest-diameter deep-water wells in the world.

The immediate customer for Ormen Lange gas is the UK – by 2010, the field will supply the country with 20% of its gas, increasing its energy supplies dramatically. With North Sea gas fields ageing and its energy needs rising, the UK sees a special significance in Ormen Lange. But Ormen Lange’s pipeline is also connected to the North Sea pipeline serving other countries in Europe, such as Belgium, Germany and France. Its gas is expected to boost energy supplies there too eventually. The field’s potential daily output of 70 million cubic metres of gas (2,472 million cubic feet) will help make Norway the world’s second biggest gas exporter after Russia.