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Freezing temperatures, immense water pressure and pitch darkness all make producing oil and gas from deep water a major technical challenge.
Around 120 km (75 miles) off the coast of Norway, the Ormen Lange deep-water project operates in sub-zero temperatures, a powerful sea swell and frequent storms. Yet almost three kilometres (over a mile) below the surface of the North Sea, engineers have found a safe way to unlock oil and gas resources.
Ormen Lange, named after the largest known Viking ship, operates without a platform. High pressure in the reservoir pushes natural gas produced there up a steep incline on the seabed to the processing facility on shore. But challenges exist.
“Low temperatures combined with high pressure in the pipes could cause blockages to form,” says Magnus Schønning, a Shell Water System Process Engineer.
To overcome this, Magnus and his colleagues inject a glycol-based liquid into the pipes. This dilutes any water in the pipes and alters the pressure and temperature required to turn it into ice-like hydrates. When it flows back to shore, the anti-freeze is separated out and recycled into the system.
As more gas is extracted over time, pressure in the reservoir is falling. Engineers have therefore taken a new approach, using a so-called underwater compressor that will maintain reservoir pressure so gas continues to flow to shore. The compressor uses the first technology of its kind.
Thousands of kilometres away, the Parque das Conchas deep-water project off Brazil’s coast had a similar challenge. Remote-controlled submarines helped to install six 1,500-horsepower electric pumps on the seabed. Each pump has the power of a Formula One engine. In an industry first, machines separate gas from oil before the pumps drive the oil to the surface. The Perdido project in the Gulf of Mexico – the world’s deepest offshore oil and gas production platform – uses the same approach.
Two tugboats towed the 22,000-tonne Perdido spar to its final location in the Gulf of Mexico
The Gumusut-Kakap platform off the coast of Sabah, Malaysia in the South China Sea will produce oil from 19 deep-water wells. Tropical storms are common in this region. To anchor the platform securely, engineers used a remote-controlled robot to attach it to four giant mooring lines, each weighing 150 tonnes. The lines secure the platform against waves of up to eight metres (25 feet) and winds that can gust at hundreds of kilometres an hour.
Strong storms also pose challenges in the Gulf of Mexico. Perdido’s nine mooring lines are designed to withstand the type of storm likely to occur once in 1,000 years, such as the most destructive hurricane in US history, Katrina. This hit the Shell Mars platform in 2005, toppling the drilling rig and damaging production facilities. Repairs took one million working hours and saw the first repair of a pipeline at a depth of 600 metres (nearly 2,000 feet) using a remote-controlled robot.
The Perdido spar — a buoyant platform nearly twice as tall as the Statue of Liberty and as heavy as around 10,000 large cars — is designed to stay upright even if it disconnects from its moorings. Even during storms it moves up and down only a few metres with the ocean’s swell. Only about 10%of it is visible above the waterline. The heavy bulk below the waterline gives it the stability to keep it straight; it is designed to tilt no more than 14 degrees even in the heaviest storms.
Stones is our newest development in the Gulf of Mexico and will host the deepest production facility in the world, at around 2,900 metres (9,500 feet) of water. The floating production facility will include a rotating turret that allows the ship-like vessel to turn, like a weathervane, with the force of wind and sea during normal weather conditions. If a heavy storm or hurricane approaches, the facility can disconnect its mooring lines and oil transport lines from the well system and sail to safe areas until the storm passes.