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US RE49,680 E1Granted
Systems and methods for spread spectrum distributed acoustic sensor monitoring
AssigneeAdelos, Inc.
InventorsChristopher Stokely, Neal G. Skinner, Leonardo De Oliveira Nunes
Life of this patent
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Abstract
A method and device for monitoring oil field operations with a fiber optic distributed acoustic sensor (DAS) that uses a continuous wave laser light source and modulates the continuous wave output of the laser light source with pseudo-random binary sequence codes.
Claims27
A system for monitoring regions of interest for occurrences that generate acoustic perturbations, comprising:
- a. an optical fiber span positioned into a region of interest;
- b. a light source for generating a continuous coherent signal of a pre-determined wavelength into the optical fiber;
- c. a pseudo-random binary code sequence generator driven by a master clock;
- d. an optical modulator having first and second ports for receiving the primary coherent light signal from the light source and a generated pseudo-random binary codes from the pseudo-random binary code sequence generator to produce a modulated light signal;
- e. wherein the pseudo-random binary sequence codes are binary sequences of ones and negative ones;
- f. and wherein the pseudo-random binary sequence codes are periodic with a period of Tb and the minimum period that the code stays at a certain value is Tc;
- g. and wherein the fiber optic cable length L, the desired spatial sampling Δz, and the acoustic signal bandwidth σA are specified in advance for the application;
- and
- i. N is chosen so that NTc=Tb;
- ii. Tb is chosen so that
- T
- b
- =
- 2
-
- L
- c
- L
- +
- ρ
- ,
- where ρ is small compared to
- 2
-
- L
- c
- L
- ;
- and
- iii. Tc is chosen so that
- Δ
- z
- =
- c
- L
- ϵ
- =
- C
- L
- T
- c
- ;
- h. an optical circulator/coupler to receive the modulated light signal from the optical modulator and pass it into the optical fiber span positioned into the region of interest;
- i. a detector system driven by the master clock for de-modulating, correlating, and de-multiplexing returned backscattered Rayleigh signals from the optical fiber span positioned into the region of interest, wherein the detector system has a processor to detect coherent Rayleigh noise generated by the optical fiber span positioned in the region of interest to identify acoustic events in the regions of interest;
- and
- j. wherein the returned backscattered Rayleigh signals from the optical fiber span positioned into the region of interest are directed to the detector system by the optical circulator/coupler.
43 more elements
A method for monitoring regions of interest for occurrences that generate acoustic perturbations, comprising:
- a. deploying a fiber optic cable into a region of interest;
- b. transmitting a continuous wave laser light source through the fiber optic cable;
- c. modulating the continuous wave output of the laser light source with pseudo-random binary sequence codes;
- wherein the pseudo-random binary sequence codes are binary sequences of ones and negative ones;
- d. and wherein the pseudo-random binary sequence codes are periodic with a period of Tb and the minimum period that the code stays at a certain value is Tc;
- e. and wherein the fiber optic cable length L, the desired spatial sampling Δz, and the acoustic signal bandwidth σA are specified in advance for the application;
- and
- i. N is chosen so that NTc=Tb;
- ii. Tb is chosen so that
- T
- b
- =
- 2
-
- L
- c
- L
- +
- ρ
- ,
- where ρ is small compared to
- 2
-
- L
- c
- L
- ;
- and
- iii. Tc is chosen so that
- Δ
- z
- =
- c
- L
- ϵ
- =
- C
- L
- T
- c
- .
- f. detecting backscattered Rayleigh signals from the deployed fiber optic cable;
- and
- g. using the detected backscattered Rayleigh signals to identify and measure the acoustic perturbations from locations in the region of interest.
41 more elements
A system, comprising:
- a light source configured to generate a continuous coherent signal of a predetermined wavelength into an optical fiber;
- a pseudo-random binary code sequence generator configured to be driven by a master clock;
- an optical modulator having first and second ports configured to receive the primary coherent light signal from the light source and a generated pseudo-random binary codes from the pseudo-random binary code sequence generator to produce a modulated light signal;
- wherein the pseudo-random binary sequence codes are binary sequences of ones and negative ones;
- and wherein the pseudo-random binary sequence codes are periodic with a period of Tb and the minimum period that the code stays at a certain value is Tc;
- and wherein an optical-fiber length L, a desired spatial sampling Δz, and an acoustic signal bandwidth σA are specified in advance for the application;
- and
- N is chosen so that NTc=Tb;
- Tb is chosen so that
- Tb
- =
- 2
-
- L
- c
- L
- +
- ρ
- ,
- where ρ is small compared to
- 2
-
- L
- c
- L
- ;
- and
- Tc is chosen so that
- Δ
-
- z
- =
- c
- L
- ∈
- =
- C
- L
- T
- c
- ;
- an optical circulator/coupler configured to receive the modulated light signal from the optical modulator and to pass it into the optical fiber;
- a detector system configured to be driven by the master clock for de-modulating, correlating, and de-multiplexing returned backscattered Rayleigh signals from the optical fiber, wherein the detector system has a processor configured to detect coherent Rayleigh noise generated by the optical fiber to identify acoustic events;
- and
- wherein the optical circulator/coupler is configured to direct the returned backscattered Rayleigh signals from the optical fiber to the detector system.
42 more elements
A method, comprising:
- modulating a continuous-wave light beam with pseudo-random binary sequence codes;
- transmitting the modulated continuous-wave light beam through a fiber-optic cable;
- wherein the pseudo-random binary sequence codes are periodic with a period of Tb and the minimum period of each code is Tc;
- and wherein a length of the fiber-optic cable is L, a spatial sampling period along the fiber is Δz, and a bandwidth of a sensed acoustic perturbation is σA;
- and
- N is chosen so that NTc=Tb;
- Tb is chosen so that
- T
- b
- =
- 2
-
- L
- c
- L
- +
- ρ
- ,
- and
- Tc is chosen so that
- Δ
-
- z
- =
- c
- L
- ∈
- =
- C
- L
- T
- c
- ;
- detecting backscattered Rayleigh signals from the fiber optic cable;
- and
- using the detected backscattered Rayleigh signals to identify and to measure one or more acoustic perturbations from one or more locations along the fiber-optic cable.
33 more elements
Dependencies are inferred from the claim text.