Enhanced backscatter fiber with tapering enhancement

Patent metadata

Field	Value
Publication number	US-2023033128-A1
Application number	US-202117386871-A
Country	US
Kind code	A1
Filing date	Jul 28, 2021
Priority date	Jul 28, 2021
Publication date	Feb 2, 2023
Grant date	—

Abstract

An optical system performs a method for measuring an acoustic signal in a wellbore. The optical system includes a light source, an optical fiber and a detector. The light source generates a light pulse. The optical fiber has a first end for receiving the light pulse from the light source and a plurality of enhancement scatterers spaced along a length of the optical fiber for reflecting the light pulse. A longitudinal density of the enhancement scatterers increases with a distance from the first end to increase a signal enhancement generated by the enhancement scatterers distal from the first end. The detector is at the first end of the optical fiber and measures a reflection of the light pulse at the enhancement scatterers to determine the acoustic signal.

First claim

What is claimed is:

1 . An optical system for measuring an acoustic signal in a wellbore, comprising:
a light source for generating a light pulse; an optical fiber having a first end for receiving the light pulse from the light source and a plurality of enhancement scatterers spaced along a length of the optical fiber for reflecting the light pulse, wherein a longitudinal density of the enhancement scatterers increases with a distance from the first end to increase a signal enhancement generated by the enhancement scatterers distal from the first end; and a detector at the first end for measuring a reflection of the light pulse at the enhancement scatterers to determine the acoustic signal.

2 . The optical system of claim 1 , wherein the plurality of enhancement scatterer includes a broadband Fiber Bragg grating.

3 . The optical system of claim 2 , wherein the light source is a laser and a reflection bandwidth of the broadband Fiber Bragg grating is greater than a bandwidth of the laser and includes a central wavelength of the laser.

4 . The optical system of claim 1 , wherein the longitudinal density of the scatterers in the optical fiber increases as one of: (i) an exponential function; (ii) an approximately exponential function; (iii) a linear function; and (iv) a non-linear function.

5 . The optical system of claim 1 , wherein a signal enhancement from a gauge length of the optical fiber increases with distance of the gauge length from the light source in relation to a longitudinal density of enhancement scatterers within the gauge length.

6 . The optical system of claim 1 , wherein the light source, optical fiber and detector are used as a Distributed Acoustic Sensing system.

7 . The optical system of claim 1 , wherein the number of enhancement scatterers in the optical fiber is greater than or equal to 100.

8 . The optical system of claim 1 , wherein a first longitudinal density of enhancement scatterers within a first gauge length at a first location near the light source is less than a second longitudinal density of enhancement scatterers within a second gauge length at a second location away from the light source, wherein a signal enhancement from the second gauge length is greater than a signal enhancement from the first gauge length.

9 . A method for obtaining an acoustic measurement in a wellbore, comprising:
transmitting a pulse of light from a light source into a first end of an optical fiber, the optical fiber having a plurality of enhancement scatterers spaced along a length of the optical fiber for enhancing the light signal, wherein a longitudinal density of the enhancement scatterers decreases with a distance from the first end to increase a signal enhancement generated by enhancement scatterers distal from the first end; and receiving a reflection of the light pulse from the enhancement scatterers at a detector at the first end to determine the acoustic signal.

10 . The method of claim 9 , wherein the plurality of enhancement scatterer includes a broadband Fiber Bragg grating.

11 . The method of claim 10 , wherein the light source is a laser and a reflection bandwidth of the broadband Fiber Bragg grating is greater than a bandwidth of the laser and includes a central wavelength of the laser.

12 . The method of claim 9 , wherein the light source is a laser and a bandwidth of the enhancement scatterer is greater than a bandwidth of the laser.

13 . The method of claim 9 , wherein the density of the scatterers in the optical fiber decreases as one of: (i) an exponential function; (ii) an approximately exponential function; (iii) a linear function; and (iv) a non-linear function.

14 . The method of claim 9 , wherein a signal enhancement from a gauge length of the optical fiber increases with distance of the gauge length from the light source in relation to a longitudinal density of enhancement scatterers within the gauge length.

15 . The method of claim 9 , wherein a first longitudinal density of enhancement scatterers within a first gauge length at a first location near the light source is less than a second longitudinal density of enhancement scatterers within a second gauge length at a second location away from the light source, wherein a signal enhancement from the second gauge length is greater than a signal enhancement from the first gauge length

Assignees

• Wysocki Paul
• Provenzano Dan
• Li Zhao
• Baker Hughes Oilfield Operations Llc

Inventors

• Wysocki Paul
• Provenzano Dan
• Li Zhao

Classifications

• G02B6/0208

  characterised by their structure, wavelength response (G02B6/02114, G02B6/02171, G02B6/02195 take precedence; multiple layer cores or claddings G02B6/036, protective coverings G02B6/4429) · CPC title

• G01D5/35361

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

• G01D5/35316

  using a Bragg gratings · CPC title

• G01V1/40 Primary

  specially adapted for well-logging · CPC title

• G01H9/004 Primary

  using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125) · CPC title