Gas Spring Compensation Marine Acoustic Vibrator

• US 20140340985A1
• Filed: 12/31/2013
• Published: 11/20/2014
• Est. Priority Date: 05/15/2013
• Status: Active Grant

• Current Assignee: PGS Geophysical As (PGS ASA)
• Original Assignee: PGS Geophysical As (PGS ASA)
• Inventors: Tenghamn, Stig Rune Lennart, Snodgrass, Jonathan David, Lfgren, Bo Carl Fredrik, Ryttersson, Karl-Henrik
• Granted Patent: US 9,864,080 B2
• Time in Patent Office: Days
• US Class Current: 367/15
• CPC Class Codes: G01V 1/135 by deforming or displacing surfaces of enclosures , e.g. by hydraulically driven vibroseis™
• CPC Class Codes: G01V 1/145 by deforming or displacing surfaces , e.g. by mechanically driven vibroseis™
• CPC Class Codes: G01V 1/38 specially adapted for water-covered areas G01V1/28 takes precedence
• CPC Class Codes: G10K 9/121 Flextensional transducers

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.

Claims

1. A marine acoustic vibrator, comprising:

an outer shell;

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.

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 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.

5. The marine acoustic vibrator of claim 1, 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.

6. The marine acoustic vibrator of claim 5, 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 5, 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 fixture coupled to the flextensional shell, wherein the driver has a first end attached to the outer shell and a second end attached to the fixture.

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

10. A marine acoustic vibrator, comprising:

a flextensional outer shell;

a fixture coupled to the flextensional outer shell;

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.

11. The marine acoustic vibrator of claim 10, 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.

12. The marine acoustic vibrator of claim 10, further comprising a gas flow restrictor disposed inside the outer shell.

13. The marine acoustic vibrator of claim 12, 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.

14. The marine acoustic vibrator of claim 13, 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.

15. The marine acoustic vibrator of claim 12, wherein the variable gas restrictor is attached to the fixture.

16. 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; and

detecting the acoustic energy originating from the acoustic vibrator.

17. The method of claim 16, wherein the acoustic vibrator is towed at a first depth of from about 0 meters to about 300 meters.

18. The method of claim 17, 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.

19. The method of claim 16, wherein restricting gas flow in the acoustic vibrator comprises moving a plate to at least partially obstruct holes in another plate.

20. The method of claim 16, 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.

21. The method of claim 16, 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.

22. The method of claim 16, further comprising:

producing a geophysical data product from the detected acoustic energy indicative of certain properties of subsurface rock below the body of water.