Shell World Online
Tireless workers of the deep sea
Deep below the sea, where the sun cannot penetrate and the pressure is too much for a diver to bear, unmanned submarines perform vital tasks to keep the oil and gas flowing.
September 21, 2007
by WENDEL BROERE
Installing equipment for onshore oil or gas wells is a straightforward, everyday activity. Not so when the wells are hundreds or thousands of metres below the sea where the sun’s rays cannot penetrate and the crushing pressure is too much for a human diver to bear.
In the dark, ice-cold ocean depths, remote-controlled submarines are the eyes and hands of workers. They do everything from mapping the sea floor to installing, inspecting and cleaning equipment. They can even cut through steel.
These unmanned subs are crucial tools for oil and gas companies, which are venturing into ever-deeper water in search of new resources as global energy demand rises and the number of untapped reservoirs on shore dwindles. They make it possible to work 3,000-4,000 metres (9,842-13,123 feet) below the waves. First developed by the military in the 1960s, they were adopted by the oil and gas industry almost 20 years later when offshore activities took off. More than 600 are now in use in the industry.
Remote-control subs come in all shapes and sizes, ranging from “Eyeballs”, a refrigerator-sized model used for seeing at depths of a few hundred metres, to heavy-duty vehicles weighing as much as several tonnes that are used to dig trenches for laying pipes on the ocean floor. These car-sized models have 250-horsepower motors.
The typical submarine consists of an aluminium chassis, several propellers for thrust, powerful lights, up to eight cameras, mapping devices and two articulated, robot-like arms that can lift 100 kilograms (220 pounds) each. Grasping claws, cutting wheels, high-pressure water jets and other interchangeable tools attach to the arms. Electrical power – up to 500 volts – feeds through a tether connecting the sub to a ship or platform on the surface. In most cases, a crew of three controls the vehicle. One steers the sub, another operates the camera, sonar and other equipment, while a third manages the winch to lower it to the seabed.
Energy companies rent the unmanned subs, along with their crews and mother ships, from a dozen or so contracting companies. It takes two hours to lower an unmanned submarine 2,500 metres (8,200 feet) to the sea floor. Using acoustic signals and video images, the pilot guides it using a joystick on a console. Digital cameras positioned at different angles transmit images back to the surface through a fibre-optic cable in the tether. The crews work in shifts to make maximum use of the sub, given daily rental costs for equipment and crew rising to thousands of dollars.
Going deeper
Shell mainly uses them for inspection, installation and maintenance work in the North Sea, the Far East, off West Africa and in the Gulf of Mexico. They also help speed repairs, such as those needed after hurricane Katrina severely damaged equipment in the Gulf. The earliest deep-water fields are now about 30 years old and as installations on the sea floor age, the need for maintenance increases. Subs can determine if pipelines are damaged or corroding, for example, and help with repairs.
Technology has come a long way since the early days when the subs were used only for inspections and were little more than a mobile camera with lights. Before the advent of powerful computers and fibre-optic cables, data was transmitted through copper cables whose pin connectors were very sensitive to seawater. Even a small short circuit could cause a loss of power, leaving the submarine adrift. The tether would sometimes end up wrapped around the legs of a platform, or get stuck in a ship’s propeller, pulling in the submarine and destroying it.
In the future, a new generation of submarines will reach even greater depths than today’s models and become more autonomous. Scientists at the Woods Hole Oceanographic Institution in the USA are already testing an unmanned submarine to explore the most remote regions of the world’s oceans, to depths of nearly 11,000 metres (36,000 feet) – deeper than Mt Everest is high. Moreover, the sub will be able to detach from its tether and swim freely part of the time.
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