Unknown tag: drilling
Continuing this week is the factual series that examines the evolution of modern engineering. This edition studies six developments that have made the construction of a giant floating oil rig possible. The 45,000-ton Perdido platform lies in the Gulf of Mexico with pipes stretching 3,000 metres into the sea. This feat of offshore engineering is largely due to six design breakthroughs stretching back to the first oil rig over water in 1891.
In the Gulf of Mexico, engineers prepare to float a state-of-the-art oil rig to a location 350km from the shore. When fully assembled, the Perdido rig will weigh 45,000 tons and float 2,380m above the surface. From there it will tap into three new oilfields. The huge assembly operation involves flipping the top part of the rig upright in the water and then using a floating crane to lift the 10,000-ton upper deck into place.
This modern-day achievement is only possible thanks to over a century of technological innovation. The first breakthrough came in Ohio in 1891, when prospectors decided to tap oil underneath the man-made Grand Lake St Mary.
Despite being only two metres deep, the lake presented a major challenge to workers who had never drilled through water. A typical 'percussion' drill was ineffective in water, so drillers tackled the problem by sealing it inside an air-tight tube.
The next breakthrough was the foundation of oil rigs in the open sea. In 1948, the Grand Isle 18 platform was anchored in 14m of water off the coast of Louisiana. The structure relied on hollow steel legs that served as guide frames for pins that anchored the rig to the sea floor. "It was a huge structure - the 'giant of the Gulf' as they called it at the time - and they realised that they could put living quarters on top," says one expert. This meant that workers could spend up to a week at a time offshore, thus increasing the rig's productivity.
The third major leap was the design of oil rigs that could stand firm on the ocean floor. The Beryl Alpha rig, constructed in the 1970s, has a massive base cast in concrete, which - unlike steel - does not flex. Engineers found an innovative way of using a hydraulic 'climbing frame' to cast the base as one solid block, making it strong enough to withstand the currents of the North Sea.
Further innovation came with the complex assembly of the Cognac rig in the Gulf of Mexico.
This 310m-high steel structure was built in four parts underwater. "Cognac was pushing the limits of deep-sea design," says one expert. Technology from the space programme was incorporated as computer-controlled barges lowered the sections into place. But some jobs still had to be completed by deep-sea divers. To minimise the risk of 'the bends', these divers were kept in a pressurised environment for a week, followed by two weeks in a decompression chamber.
The 1990s saw further advances with the launch of a unique floating oil platform called the Augur.
This design enabled rigs to drill at even greater depths. The success of the platform in the Gulf of Mexico opened up hitherto unexplored realms.
"The entire industry was abuzz about Augur and the whole perspective on the potential of deepwater changed," says an expert. All of these achievements, and further improvements in fire safety following the Piper Alpha disaster, have found their way into the ground-breaking design of the Perdido oil rig.