Detecting broadside acoustic signals with a fiber optical distributed acoustic sensing (DAS) assembly

Patent metadata

Field	Value
Publication number	US-10139269-B2
Application number	US-201715677640-A
Country	US
Kind code	B2
Filing date	Aug 15, 2017
Priority date	Dec 15, 2011
Publication date	Nov 27, 2018
Grant date	Nov 27, 2018

Abstract

A distributed fiber optic acoustic sensing system includes a cable having a cable length. The cable has an elongated body having an outer surface, and at least one straight optical fiber extending parallel to a longitudinal axis of the cable along the cable length; and one or more non-straight optical fibers, such as two orthogonal sinusoidal optical fibers extending along the cable length, or a helically wrapped optical fiber extending along the cable length. The sensing system further has light transmitting and receiving means optically connected to the optical fibers.

First claim

We claim:

1. A distributed fiber optic acoustic sensing system comprising:
a towed streamer cable having a cable length, the towed streamer cable comprising:
an elongated body having an outer surface;
at least one straight optical fiber extending parallel to a longitudinal axis of the towed streamer cable along the cable length; and
at least one helically wrapped optical fiber extending along the cable length and having a first predetermined wrap angle; and

light transmitting and receiving means optically connected to said at least one straight optical fiber and the least one helically wrapped optical fiber for, respectively, transmitting optical signals into each of the at least one straight and at least one helically wrapped optical fibers and receiving a backscattered component of said signals out of the at least one straight and at least one helically wrapped optical fibers.

2. The distributed fiber acoustic sensing system according to claim 1 , wherein the first predetermined wrap angle is measured with respect to a plane normal to the axis of the elongated body and wherein the first predetermined wrap angle is smaller than 90°.

3. The distributed fiber acoustic sensing system according to claim 1 , wherein the system further comprises a first sheath layer on the outside of the elongated body and covering the elongated body and the first straight optical fiber.

4. The distributed fiber acoustic sensing system according to claim 3 , wherein the towed streamer cable further comprises at least a second helically wrapped optical fiber wrapped around the outside of the first sheath layer.

5. The distributed fiber acoustic sensing system according to claim 4 , wherein the first helically wrapped optical fiber and the second helically wrapped optical fiber define different wrap angles.

6. The distributed fiber acoustic sensing system according to claim 5 , wherein the wrap angles are measured with respect to a plane normal to the axis of the elongated body and wherein the first predetermined wrap angle is 90° and the second predetermined wrap angle is less than 45°, or wherein the second predetermined wrap angle is 90° and the first predetermined wrap angle is less than 45°.

7. The distributed fiber acoustic sensing system according to claim 6 , wherein the towed streamer cable further comprises a third helically wrapped optical fiber disposed on the outer surface at a wrap angle between 90° and 45°.

8. The distributed fiber acoustic sensing system according to claim 1 , wherein the towed streamer cable is adapted to measure seismic signals along the towed streamer cable as a function of incidence angle of the seismic signals.

9. The distributed fiber acoustic sensing system according to claim 1 , wherein the at least one straight optical fiber is arranged in the towed streamer cable.

10. The distributed fiber acoustic sensing system according to claim 1 , further comprising:
means for transmitting optical signals into each of the at least one straight and at least one helically wrapped optical fibers;
means for receiving backscattered signals out of each of the at least one straight and at least one helically wrapped optical fibers consisting of a component of said optical signals which component has been backscattered from impurities or inhomogeneities in each of the at least one straight and at least one helically wrapped optical fibers;
means for observing changes in the backscattered signals caused by axial stretching and compressing of each of the at least one straight and at least one helically wrapped optical fibers caused by an incident wave;
means for comparing the backscattered signals of the at least one straight optical fiber and the at least one helically wrapped optical fiber; and
means for determining, based on the comparing of the backscattered signals, a direction of wave propagation of the incident wave with respect to the longitudinal axis of the towed streamer cable for detecting broadside waves and axial waves distinguishably.

11. A distributed fiber optic acoustic sensing system comprising:
a towed streamer cable having a cable length, the towed streamer cable comprising:
an elongated body having an outer surface;
at least one straight optical fiber extending parallel to a longitudinal axis of the towed streamer cable along the cable length; and
at least two orthogonal sinusoidal optical fibers extending along the cable length; and

light transmitting and receiving means optically connected to said at least one straight optical fiber and at least two orthogonal sinusoidal optical fibers for, respectively, transmitting optical signals into each of the at least one straight and at least at least two orthogonal sinusoidal optical fibers and receiving a backscattered component of said signals out of the at least one straight and at least at least two orthogonal sinusoidal optical fibers.

12. The distributed fiber acoustic sensing system according to claim 11 , further comprising:
means for transmitting optical signals into each of the at least one straight and at least at least two orthogonal sinusoidal optical fibers;
means for receiving backscattered signals out of the each of the at least one straight and at least at least two orthogonal sinusoidal optical fibers consisting of a component of said optical signals which component has been backscattered from impurities or inhomogeneities in each of the at least one straight and at least at least two orthogonal sinusoidal optical fibers;
means for observing changes in the backscattered signals caused by axial stretching and compressing of the each of the at least one straight and at least at least two orthogonal sinusoidal optical fibers caused by an incident wave;
means for comparing the backscattered signals of the at least one straight optical fiber and the at least two orthogonal sinusoidal optical fibers; and
means for determining, based on the comparing of the backscattered signals, a direction of wave propagation of the incident wave with respect to the longitudinal axis of the towed streamer cable for detecting broadside waves and axial waves distinguishably.

13. A distributed fiber optic acoustic sensing system comprising:
a cable having a cable length comprising:
an elongated body having an outer surface;
at least one straight optical fiber extending parallel to a longitudinal axis of the cable along the cable length; and
at least one helically wrapped optical fiber extending along the cable length and having a first predetermined wrap angle; and

light transmitting and receiving means optically connected to said at least one straight optical fiber and the least one helically wrapped optical fiber for, respectively, transmitting optical signals into each of the at least one straight and at least one helically wrapped optical fibers and receiving a backscattered component of said signals out of the at least one straight and at least one helically wrapped optical fibers;

wherein the cable is an ocean bottom cable (OCB) deployed on the seabed.

14. A distributed fiber optic acoustic sensing system comprising:
a cable having a cable length, the cable comprising:
an elongated body having an outer surface;
at least one straight optical fiber extending parallel to a longitudinal axis of the cable along the cable length; and
at least two orthogonal sinusoidal optical fibers extending along the cable length; and

light transmitting and receiving means optically connected to said at least one straight optical fiber and at least two orthogonal sinusoidal optical fibers for, respectively, transmitting optical signals into each of the a

Assignees

• Shell Oil Co

Inventors

• Den Boer Johannis Josephus
• Mateeva Albena Alexandrova
• Pearce Jeremiah Glen
• Mestayer Jeffery Joseph
• Birch William
• Lopez Jorge Louis
• Hornman Johan Cornelis
• Kuvshinov Boris Nikolaevich

Classifications

• G01V1/226 Primary

  Optoseismic systems · CPC title

• G01H9/006 Primary

  the vibrations causing a variation in the relative position of the end of a fibre and another element · CPC title

• G01V1/40 Primary

  specially adapted for well-logging · CPC title

• G01H9/004

  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

• G01S3/801 Primary

  Details {(G01S3/82, G01S3/84, G01S3/86 take precedence)} · CPC title