Arrayed wave division multiplex to extend range of IOFDR fiber bragg sensing system

摘要

An apparatus for performing a measurement of a downhole property includes an optical fiber having a first section that has a first set of fiber Bragg gratings with a first resonant wavelength inscribed therein and a second section that has a second set of fiber Bragg gratings with a second resonant wavelength different from the first resonant wavelength inscribed therein. The second section is in series with the first section. An optical interrogator emits a swept-wavelength frequency domain light signal having varying wavelength amplitude modulation into the optical fiber, receives a frequency domain return light signal, and transforms the frequency domain return signal into a time domain to determine a resonant wavelength shift of each fiber Bragg grating and the corresponding location of each interrogated fiber Bragg grating. A processor converts the resonant wavelength shift of each interrogated fiber Bragg grating into the downhole property measurement.

主权项

1. An apparatus for performing a measurement of a downhole property, the apparatus comprising:
an optical fiber having a first section that has a first set of fiber Bragg gratings with a first resonant wavelength inscribed therein and a second section that has a second set of fiber Bragg gratings with a second resonant wavelength different from the first resonant wavelength inscribed therein, the second section being in series with the first section, a difference between the second resonant wavelength and the first resonant wavelength being greater than a dynamic wavelength range of each of the fiber Bragg gratings in the first set of fiber Bragg gratings; an optical interrogator in optical communication with the optical fiber and configured to: emit a frequency domain light signal into the optical fiber, the frequency domain light signal comprising a swept wavelength for a first time duration and a chirp comprising a modulation of amplitude with a varying of wavelength for a second time duration that is less than the first time duration; receive a frequency domain return light signal from the optical fiber due to the emitted frequency domain light signal, the frequency domain return light signal comprising a resonant wavelength shift of each fiber Bragg grating due to the downhole property and a corresponding location of each fiber Bragg grating; and transform the frequency domain return signal into a time domain in order to determine the resonant wavelength shift of each fiber Bragg grating and the corresponding location of each interrogated fiber Bragg grating; and a processor configured to convert the resonant wavelength shift of each interrogated fiber Bragg grating into the downhole property measurement.