Systems and methods for spread spectrum distributed acoustic sensor monitoring
First Claim
Patent Images
1. 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 Δ
z, and the acoustic signal bandwidth σ
A are specified in advance for the application; and
i. N is chosen so that NTc=Tb;
ii. Tb is chosen so that
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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.
36 Citations
22 Claims
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1. A system for monitoring regions of interest for occurrences that generate acoustic perturbations, comprising:
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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 Δ
z, and the acoustic signal bandwidth σ
A are specified in advance for the application; andi. N is chosen so that NTc=Tb; ii. Tb is chosen so that - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for monitoring regions of interest for occurrences that generate acoustic perturbations, comprising:
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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 Δ
z, and the acoustic signal bandwidth σ
A are specified in advance for the application; andi. N is chosen so that NTc=Tb; ii. Tb is chosen so that - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification