At Ormen Lange there is no production platform on the surface. The turbulent waters covering the gas field off the Norwegian coast reveal nothing of the innovative production system working on the sea floor deep below, piping gas and condensate directly to a processing plant onshore at Nyhamna.
“This unusual approach helps avoid the challenges that high winds and waves could pose to safety and maintenance work,” says Pieter Swart, team leader for underwater pipelines on the project.
Engineers still faced a challenge to install the equipment on the sea floor, where a major landslide around 8,000 years ago caused a massive underwater shift in sediment. Over 240 days, they moved in 5 million tonnes of rock to level the seabed, ensuring production and pipeline system could be safely installed on solid ground.
Sections of pipeline were welded together aboard dedicated vessels and carefully lowered to the seabed. Shell uses small robotic submarines, called remotely operated vehicles (ROV) and autonomous underwater vehicles (AUV), to regularly inspect the production system and pipelines.
“The systems are designed for a long life,” says Pieter. “They are controlled from shore and run extremely efficiently at about 98% capacity.”
Freezing temperatures in pipelines at the bottom of the sea can cause water, which is produced with the gas, to form icy blockages called hydrates. Anti-freeze is pumped into the wellheads to keep the gas flowing. The anti-freeze is later recycled at the receiving onshore processing plant and re-used. An automated system – the first of its kind in deep water – delivers just the right amount for greater efficiency.
Know your reservoir
Offshore teams closely monitor changes to the reservoir rock and fluids as production progresses.
“We have a three-pronged approach to reservoir monitoring,” says Todd Noble, responsible for geophysics at Ormen Lange. “By combining different surveys we can more accurately monitor how the reservoir is changing. This provides important information on how to best manage production and future development.”