Thousands of feet under the North Sea, an array of transformers, choke manifolds, pumps and valves buzz and whir in an improvised subsea symphony. They play for a 500-pound electronic ear whose design is a closely guarded trade secret.
The ear sends the sound through an umbilical cable to a seaborne control room filled with computers and engineers dissecting every stray whoosh and hiss. They are listening for oil leaks, odd vibrations, strange cracks and other signs of trouble. “An acoustic signature from a piece of equipment is like a fingerprint from a human,” says Fabian Dawson, sales manager from GE Measurement and Control. “No two leaks or pumps are going to sound the same.” Call it Shazam for the seabed.
Dawson says that the system holds a library more than 100,000 sounds. “We can filter out the background noise, like marine life, and listen only to the things that we want to,” Dawson says. He says that the system is 10,000 times more accurate than traditional “mass balance” systems that measure differences in the amount of oil and gas flowing through the pipes to detect leaks.
GE engineers designed the eardrum of the system, which looks like a giant birdcage, from special crystals that respond to sound wave vibrations and convert them into electricity. (Engineers call this effect “piezoelectricity.”) One ear can listen to sounds within a 1,600 foot radius.
But the system does more than that. An array of attached carbon rods can detect changes in the electromagnetic field generated by electrical cables, pumps, motors and other electrical equipment, and spot ground faults or defective isolation. “You can determine the rpm of a compressor from the acoustic signal, and then you can determine how hard it is working from the electrical signal,” Dawson says. “Taken together, they will tell you what the efficiency is.”
Workers deploy the cage by lowering it down the side of a ship from a crane. They use ROVs to secure it to a piece of subsea equipment or to the sea floor. “It’s a simple, X-marks-the-spot procedure,” Dawson says.
The system is already working at some 130 sites in the North Sea operated by Statoil, ENI, and Shell, and off the coast of Africa. GE has now introduced it to American customers at the 2013 Offshore Technology Conference held this week in Houston.
The system is using powerful software and algorithms to make sense of the sounds. But like an elusive remix you’ve heard at a party, phantom noise can still creep in. “You are looking at correlations between the pieces of the equipment emitting both the electrical and the acoustic signals, and sometimes there is a signature there that you can’t trace.” Dawson says. “We call them rogue sounds.”
When that happens, the GE teams goes straight to the source, the engineers who built the equipment. “They are the experts,” Dawson says. “They know what their machines should sound like. They can recognize the rogue harmonics.”