Gas spring compensation marine acoustic vibrator

Patent metadata

Field	Value
Publication number	US-9864080-B2
Application number	US-201314145214-A
Country	US
Kind code	B2
Filing date	Dec 31, 2013
Priority date	May 15, 2013
Publication date	Jan 9, 2018
Grant date	Jan 9, 2018

Abstract

Embodiments related to restriction of gas flow in a marine acoustic vibrator to compensate for gas spring effects. An embodiment provides a marine acoustic vibrator, comprising: an outer shell; and a variable gas flow restrictor disposed within the outer shell; wherein the marine acoustic vibrator has a resonance frequency selectable based at least in part on the variable gas flow restrictor.

First claim

What is claimed is:

1. A marine acoustic vibrator, comprising:
an outer shell; and
a variable gas flow restrictor disposed within the outer shell; wherein the variable gas flow restrictor comprises a first plate comprising holes, and a second plate comprising holes, the second plate being moveable to at least partially cover the holes in the first plate;
wherein the marine acoustic vibrator has a resonance frequency selectable based at least in part on the variable gas flow restrictor.

2. The marine acoustic vibrator of claim 1 , further comprising:
a driver disposed at least partially within the outer shell and coupled thereto.

3. The marine acoustic vibrator of claim 2 , wherein the driver comprises an electro dynamic driver.

4. The marine acoustic vibrator of claim 2 , further comprising a fixture coupled to the outer shell, wherein the driver has a first end attached to the outer shell and a second end attached to the fixture.

5. The marine acoustic vibrator of claim 1 , wherein the marine acoustic vibrator has at least two resonance frequencies of about 10 Hz or lower when submerged in water at a depth of from about 0 meters to about 300 meters.

6. The marine acoustic vibrator of claim 1 , wherein the variable gas flow restrictor has an open position and a closed position, the holes in the first plate being at least partially obstructed by the second plate in the closed position, and the holes in the first plate and the holes in the second plate being aligned in the open position for maximum gas flow through the variable gas flow restrictor.

7. The marine acoustic vibrator of claim 1 , wherein the variable gas restrictor is attached to a fixture in the marine acoustic vibrator, the fixture being coupled to the outer shell.

8. The marine acoustic vibrator of claim 1 , further comprising a spring coupled to the outer shell, and masses attached to the spring.

9. The marine acoustic vibrator of claim 1 :
wherein the outer shell comprises a flextensional outer shell;
wherein the marine acoustic vibrator further comprises a fixture coupled to the flextensional outer shell;
wherein the marine acoustic vibrator further comprises a driver having a first end and a second end, wherein the first end is attached to the flextensional shaped outer shell, and the second end is attached to the fixture;
wherein a gas spring is adapted together with a mass to generate a first resonance frequency, and wherein the value of the gas spring is changed by restriction of gas flow in the marine acoustic vibrator to thereby control the first resonance frequency at depth.

10. The marine acoustic vibrator of claim 9 , wherein the marine acoustic vibrator has at least two resonance frequencies of about 10 Hz or lower when submerged in water at a depth of from about 0 meters to about 300 meters.

11. The marine acoustic vibrator of claim 9 , wherein the variable gas restrictor is attached to the fixture.

12. A method comprising:
towing an acoustic vibrator in a body of water;
triggering the acoustic vibrator to generate acoustic energy in the body of water;
restricting gas flow in the acoustic vibrator to control a first resonance frequency of the acoustic vibrator, wherein restricting gas flow in the acoustic vibrator comprises moving a plate to at least partially obstruct holes in another plate; and
detecting the acoustic energy originating from the acoustic vibrator.

13. The method of claim 12 , wherein the acoustic vibrator is towed at a first depth of from about 0 meters to about 300 meters.

14. The method of claim 13 , further comprising:
towing the acoustic vibrator at a second depth, wherein the gas flow is restricted in the acoustic vibrator when towed at the first depth such that the first resonance frequency of the acoustic vibrator is substantially constant when towing depth varies from the first depth to the second depth.

15. The method of claim 12 , further comprising opening a variable gas flow restrictor to allow increased gas flow in the acoustic vibrator as the acoustic vibrator is lowed in the body of water.

16. The method of claim 12 , further comprising increasing an shell internal gas pressure of the acoustic vibrator to equalize the shell internal gas pressure with the water pressure at depth.

17. The method of claim 12 , further comprising:
producing a geophysical data product from the detected acoustic energy indicative of certain properties of subsurface rock below the body of water.

Assignees

• Pgs Geophysical As

Inventors

• Tenghamn Stig Rune Lennart
• Snodgrass Jonathan David
• Löfgren Bo Carl Fredrik
• Ryttersson Karl-Henrik

Classifications

• G10K9/121

  Flextensional transducers · CPC title

• G01V1/145

  by deforming or displacing surfaces {, e.g. by mechanically driven vibroseis™} · CPC title

• G01V1/38

  specially adapted for water-covered areas (G01V1/28 takes precedence) · CPC title

• G01V1/135 Primary

  by deforming or displacing surfaces of enclosures {, e.g. by hydraulically driven vibroseis™} · CPC title