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FIBER OPTICS: Under Interrogation: Where the Magic Happens

Image courtesy of Fotech Solutions.
An interrogation unit using a distributed acoustic sensing system, above, is capable of sending pulses of light down the fiber cable at rates of tens of thousands per second. The light travels so fast that it returns to the unit with downhole data before the next pulse is even fired off.

Downhole fiber-optic systems work by using a small laser that fires off a pulse of light through hair-thin cables made of silica glass. In a fraction of a second, the light travels through the cable and loops back to an optical receiver, delivering a mass of signals and noise that are then sorted out by advanced electronics. For some applications, this process is repeated up to 16,000 times a second—much faster pulse rates are possible, but the top rate is limited by the fiber’s length. And aside from the cable, all the action is taking place in the interrogator unit, a box resembling a computer server that sits on the surface, not far from the wellhead.

The roots of the technology inside the interrogator units can be traced back to 15 years ago during the North American telecommunications boom that suddenly went bust in the early 2000s. Before the bubble burst, billions of dollars were poured into developing smaller lasers, sensitive optical electronics, and reliable interpretation software. This massive investment laid the foundation for the technology’s entry into the oil and gas industry.

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FIBER OPTICS: Under Interrogation: Where the Magic Happens

Trent Jacobs, JPT Senior Technology Writer

01 August 2014

Volume: 66 | Issue: 8

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