Unlocking energy from the deep ocean

The water depth of nearly three kilometres (1.9 miles) and isolated location of the Perdido platform posed major challenges to production. So did the dispersed nature of the reservoirs and low pressure in the porous rock that hinders the flow of oil and natural gas.

Cutting deep-water drilling time

Only a few floating rigs can drill down far enough to reach the reservoirs: the Noble Clyde Boudreaux is one of them. It takes six 13,500-horsepower generators to power the drills on this 29,000-tonne craft that soars six stories above the water.

With two drilling decks instead of one, it operates faster than regular rigs. It can work on one well and simultaneously drill a new one. Precision drilling at these depths demands great skill — operators on the rig use joysticks to guide the drill-bits below, driving them up to three kilometres (1.9 miles) beneath the seabed to hit a target the size of a garbage bin lid.

Reducing weight

The location of the fields 320 kilometres (200 miles) from the shore means that every litre of fuel and piece of machinery must be shipped in on a 23-hour journey. Keeping the platform compact and reducing the amount of equipment needed in this isolated location is vital. 

Until recently, in a typical deep-water development each well was connected to an individual flexible pipe called a riser, which carries oil and gas to the surface. But at the Perdido project each long riser weighs 500 tonnes and the cylindrical hull, or spar, would have needed to be four times bigger to support one for each of the 22 wells directly below. So Shell engineers constructed a 44-kilometre (27-mile) network of pipelines on the ocean floor linking the wells to just five risers.

They also placed the 22 giant steel cases containing equipment to control and monitor the flow of oil on the seabed and not the deck, helping to reduce the size of the platform.

Deepest pipeline link-up

Adding to the challenges, the Perdido project’s wells sit in rugged seabed terrain, with an underwater Grand Canyon to the north, and protected sea life colonies to the south and east. That complicates the task of building a pipeline to carry Perdido’s oil and gas to shore. “We’ve really only got one path out,” says Mike Dupre, pipelines and flowlines engineer.

Instead of building a new 381-kilometre (237-mile) pipeline to the shore, engineers tapped into existing pipelines on the seabed less than half that distance away already transporting oil and gas for other fields to the north. Operators on the surface guided two remotely-controlled submarines to install new pipelines to the nearest existing ones — a 172-kilometre (107-mile) gas pipeline and a 124-kilometre (77-mile) oil pipeline. The greatest challenge was creating the connection between the new oil pipeline and the existing one at nearly 1,400 metres (4,600 feet) below sea level.

Engineers had to accomplish the whole operation without letting any oil leak into the sea. They first halted the flow of oil in the existing pipe. Then they used water to flush the section of pipe where they planned to create a new junction. Using remotely controlled robots, operators sawed through and removed an 8.6-metre (28-foot) section of the pipe.

If the team had detected an oil leak, they were ready to seal the cuts with clamps and pump in more clean water. As a further precautionary measure, they installed a giant tent over the area to keep in any fluid potentially released and transfer it to a reservoir.

Finally, the robots installed a new connection point and welded it into place. It was the deepest such tie-in ever. “We achieved this record-breaking feat without spilling a drop of oil,” says Don Nelson, subsea pipeline installation manager.