Detection of seismic signals using fiber optic distributed sensors

Patent metadata

Field	Value
Publication number	US-10113902-B2
Application number	US-201615296723-A
Country	US
Kind code	B2
Filing date	Oct 18, 2016
Priority date	May 26, 2010
Publication date	Oct 30, 2018
Grant date	Oct 30, 2018

Abstract

A fiber optic distributed vibration system for detecting seismic signals in an earth formation is provided. The system includes a fiber optic cable deployed in a borehole that extends into the earth formation and which is configured to react along its length to a seismic wave incident on the fiber optic cable from outside the borehole. An optical source launches an optical signal into the fiber optic cable while the seismic wave is incident thereon. A receiver detects coherent Rayleigh noise (CRN) produced in response to the optical signal. A processing circuit processes the detected CRN signal to determine characteristics of the earth formation.

First claim

What is claimed is:

1. A seismic event detection system in a well, comprising:
a first fiber optic cable disposed in a borehole extending from an earth surface into a formation, the first fiber optic cable configured to react along its length to incident seismic signals originating: inside the borehole and propagating through the formation and the borehole or outside the borehole and propagating through the formation;
an optical source to launch optical pulses into the first fiber optic cable while the seismic signals are incident on the first fiber optic cable; and
a data acquisition system coupled to the first fiber optic cable to detect coherent Rayleigh noise (CRN) generated in response to the optical pulses to determine characteristics of the well based on the detected CRN.

2. The system as recited in claim 1 , further comprising:
a second fiber optic cable disposed in the borehole and coupled to the optical source, the second fiber optic cable configured to react along its length to incident seismic signals,
wherein the first fiber optic cable is disposed at a first location within a transverse cross-section of the borehole and the second fiber optic cable is disposed at a second location within the transverse cross-section of the borehole that is spaced apart from the first location, and
wherein the data acquisition system detects a phase difference between seismic signals incident on the first and second fiber optic cables at each of a plurality of locations along a length of the borehole to determine characteristics of the well.

3. The system as recited in claim 1 , further comprising:
a second fiber optic cable disposed in a second borehole, the second fiber optic cable configured to react along its length to incident seismic signals originating: inside the second borehole and propagating through the formation and the borehole or outside the borehole and propagating through the formation;
a second optical source to launch optical pulses into the second fiber optic cable while the seismic signals are incident on the second fiber optic cable; and
a data acquisition system coupled to the second fiber optic cable to detect CRN generated in response to the optical pulses,
wherein the CRN generated by the first fiber optic cable is correlated with the CRN generated by the second fiber optic cable to determine characteristics of the formation.

4. The system as recited in claim 1 , wherein a hypocenter of a microseismic event is determined based on the detected CRN.

5. The system as recited in claim 1 , wherein the first fiber optic cable comprises a plurality of discrete optical sensors.

6. The system as recited in claim 5 , wherein the discrete optical sensors comprise fiber Bragg gratings spaced apart along the length of the first fiber optic cable.

7. The system as recited in claim 2 , wherein the first fiber optic cable generates a first CRN response to pressure, velocity, acceleration and/or strain and the second fiber optic cable generates a second CRN response to the same pressure, velocity, acceleration and/or strain, and wherein the data acquisition system determines characteristics of the well based on a difference between the first CRN response and the second CRN response.

8. The system as recited in claim 2 , wherein the first and second fiber optic cables are installed in a first control line.

9. The system as recited in claim 1 , wherein the first fiber optic cable comprises a pressure-sensitive material disposed along its length.

10. A method for conducting a seismic survey of a well, comprising:
launching a first optical signal into a first fiber optic cable disposed in a borehole extending from an earth surface into an earth formation;
generating a seismic wave that propagates through the well from inside or outside of the borehole; and
analyzing coherent Rayleigh noise (CRN) produced in response to the first optical signal while the seismic wave is incident along a length of the first fiber optic cable to determine characteristics of the well.

11. The method as recited in claim 10 , further comprising:
launching a second optical signal into a second fiber optic cable disposed in a borehole; and
analyzing CRN produced in response to the second optical signal while the seismic wave is incident along the length of the second fiber optic cable,
wherein characteristics of the well are determined based on the CRN produced in response to the first optical signal and the CRN produced in response to the second optical signal.

12. The method as recited in claim 11 , wherein the first fiber optic cable and the second fiber optic cable have a substantially identical construction and are disposed at different locations within a transverse cross-section of the same borehole, and wherein characteristics of the well are determined based on a phase difference in the seismic wave incident on the first and second fiber optic cables at each of a plurality of locations along a length of the same borehole.

13. The method as recited in claim 11 , wherein the first fiber optic cable is configured to react differently to pressure, velocity, acceleration and/or strain than the second fiber optic cable reacts to pressure, velocity, acceleration and/or strain.

14. A system in a well comprising:
a first optical fiber disposed in a borehole that extends from an earth surface into an earth formation, the first optical fiber configured to react to a seismic wave incident on the first optical fiber at any of a plurality of locations along its length;
a seismic source to generate a seismic wave that originates outside or inside of the borehole;
an optical source to launch an optical signal into the first optical fiber to produce a backscattered optical signal while the seismic wave is incident on the first optical fiber;
a receiver to detect coherent Rayleigh noise (CRN) in the backscattered signal; and
a processing circuit to process the CRN to determine characteristics of the well.

15. The system as recited in claim 14 , further comprising a second optical fiber disposed in a borehole extending from the earth surface into the earth formation and configured to produce a second CRN signal while the seismic wave is incident at any of a plurality of locations along a length of the second optical fiber, and wherein the processing circuit further processes the second CRN signal to determine characteristics of the well.

16. The system as recited in claim 15 , wherein the first optical fiber and the second optical fiber are disposed in the same borehole.

17. The system as recited in claim 16 , wherein the first optical fiber and the second optical fiber have a substantially identical construction and are disposed at different locations within a transverse cross-section of the same borehole, and wherein characteristics of the earth formation are determined based on a phase difference in the seismic wave incident on the first and second fiber optic cables at each of a plurality of locations along a length of the borehole.

18. The system as recited in claim 16 , wherein the first optical fiber is configured to react differently to pressure, velocity, acceleration and/or strain than the second optical fiber reacts to pressure, velocity, acceleration and/or strain, and wherein characteristics of the earth formation are determined based on a difference in the reactions.

19. The system as recited in claim 14 , wherein the seismic source is located in a second borehole that extends from the earth surface into the earth formation, wherein the sec

Assignees

• Schlumberger Technology Corp

Inventors

• Coates Richard T
• Miller Douglas E
• Hartog Arthur H
• Wilson Colin A
• Brady Dominic
• Menkiti Henry
• Auzerais Francois M
• Bradford Ian David Richard

Classifications

• G01V1/18

  Receiving elements, e.g. seismometer, geophone {or torque detectors, for localised single point measurements} · CPC title

• G01D5/35361

  using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering · CPC title

• G01V1/208

  having a continuous structure (detecting traffic G08G, transducers in general G10K) · CPC title

• G01L1/242

  the material being an optical fibre · CPC title

• G01V1/42

  using generators in one well and receivers elsewhere or vice versa (G01V1/52 takes precedence) · CPC title