FIBER OPTIC DISTRIBUTED ACOUSTIC MEASUREMENTS VIA FMCW INTERROGATION

• US 20150085610A1
• Filed: 08/19/2014
• Published: 03/26/2015
• Est. Priority Date: 09/25/2013
• Status: Abandoned Application

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Raum, Matthew Thomas, Duncan, Roger Glen, Childers, Brooks A.
• Application Number:
  US14/462,804
• Publication Number:
  US 20150085610A1
• Time in Patent Office: Days
• US Class Current: 367/25
• CPC Class Codes: G01V 1/226 Optoseismic systems
• CPC Class Codes: G01V 1/40 specially adapted for well-logging
• CPC Class Codes: G01V 2210/1234 Hydrocarbon reservoir, e.g. spontaneous or induced fracturing

Abstract

A system and method to obtain acoustic information from a borehole penetrating the earth are described. The system includes a light source to provide a continuous output beam and a modulator to modulate the continuous output beam with a modulation signal to provide a frequency modulated continuous wave (FMCW) to be sent out on an optical fiber disposed along the borehole, the optical fiber including a plurality of reflectors at known locations along the optical fiber. The system also includes a processor to process a light reflection signal from the optical fiber to determine the acoustic information.

Claims

1. A system to obtain acoustic information from a borehole penetrating the earth, the system comprising:

a light source configured to provide a continuous output beam over a selected period of time;

a modulator configured to modulate the continuous output beam with a modulation signal to provide a frequency modulated continuous wave (FMCW) to be sent out on an optical fiber disposed along the borehole, the optical fiber including a plurality of reflectors at known locations along the optical fiber; and

a processor configured to process a light reflection signal from the optical fiber to determine the acoustic information.

2. The system according to claim 1, wherein the light source is a laser.

3. The system according to claim 1, wherein the modulator is configured to modulate the continuous output beam with a modulation signal having a sinusoidal envelope whose frequency is swept linearly over time over a given range.

4. The system according to claim 1, wherein the processor is further configured to convert the light reflection signal reflected by the fiber to an electronic signal.

5. The system according to claim 4, wherein the processor is further configured to mix the electronic signal with the modulation signal and perform a Fourier transform on a resulting signal to output a detected signal in a frequency domain.

6. The system according to claim 5, wherein the processor is further configured to demodulate the detected signal to determine a displacement of each of the plurality of reflectors.

7. The system according to claim 6, wherein the processor is further configured to obtain the acoustic information based on a difference between the displacements.

8. The system according to claim 4, wherein the processor is further configured to mix the electronic signal with a time delayed version of the modulation signal and perform a Fourier transform on a resulting signal to output a detected signal in a frequency domain.

9. The system according to claim 8, wherein the processor is further configured to demodulate the detected signal to determine a displacement of each of the plurality of reflectors and to obtain the acoustic information based on a difference between the displacements.

10. A method of obtaining acoustic information from a borehole penetrating the earth, the method comprising:

disposing an optical fiber along the borehole, the optical fiber including a plurality of reflectors at known locations along the optical fiber;

modulating a continuous output beam with a modulation signal to provide a frequency modulated continuous wave (FMCW) to be sent out on the optical fiber; and

processing a light reflection signal from the optical fiber to determine the acoustic information.

11. The method according to claim 10, wherein the modulating is with a modulation signal that has a sinusoidal envelope whose frequency is swept linearly over time over a given range.

12. The method according to claim 10, wherein the processing includes converting the light reflection signal to an electronic signal.

13. The method according to claim 12, wherein the processing includes mixing the electronic signal with the modulation signal and performing a Fourier transform to output a detected signal in a frequency domain.

14. The method according to claim 13, wherein the processing includes demodulating the detected signal to determine a displacement of each of the plurality of reflectors.

15. The method according to claim 14, wherein the processing includes obtaining the acoustic information based on a difference between the displacements.

16. The method according to claim 12, wherein the processing includes mixing the electronic signal with a time delayed version of the modulation signal and performing a Fourier transform to output a detected signal in a frequency domain.

17. The method according to claim 16, wherein the processing includes demodulating the detected signal to determine a displacement of each of the plurality of reflectors and obtaining the acoustic information based on a difference between the displacements.