Method for generating spread spectrum driver signals for a seismic vibrator array using multiple biphase modulation operations in each driver signal chip

• US 20110038225A1
• Filed: 08/12/2009
• Published: 02/17/2011
• Est. Priority Date: 08/12/2009
• Status: Active Grant

• Current Assignee: PGS Geophysical As (PGS ASA)
• Original Assignee: PGS Geophysical As (PGS ASA)
• Inventors: Tenghamn, Stig Rune Lennart
• Granted Patent: US 8,335,127 B2
• Time in Patent Office: Days
• US Class Current: 367/21
• CPC Class Codes: G01V 1/005 with exploration systems emitting special signals, e.g. frequency swept signals, pulse sequences or slip sweep arrangements
• CPC Class Codes: G01V 2210/1214 Continuous
• CPC Class Codes: G01V 2210/6222 Velocity; travel time
• CPC Class Codes: G10K 9/121 Flextensional transducers

Abstract

A method for generating seismic energy for subsurface surveying include operating a first seismic vibrator above an area of the subsurface to be surveyed and operating at least a second seismic vibrator above the area substantially contemporaneously with the operating the first seismic vibrator. The first and the second vibrators each have a different selected frequency response. The first and second vibrators each is operated by a same direct sequence spread spectrum signal, wherein a different number of modulation operations for each logical value in the direct sequence spread spectrum signal is selected for each vibrator.

Claims

1. A method for generating seismic energy for subsurface surveying, comprising:

operating a first seismic vibrator above an area of the subsurface to be surveyed; and

operating at least a second seismic above the area substantially contemporaneously with the operating the first seismic vibrator, the first and the second vibrators each having a different selected frequency response range, the first and second vibrators each operated by a same direct sequence spread spectrum driver signal, wherein a different number of modulation operations for each logical value in the direct sequence spread spectrum signal is selected for each vibrator.

2. The method of claim 1 wherein each number of modulation operations is selected to correspond to the frequency response range of each vibrator.

3. The method of claim 1 wherein the direct sequence spread spectrum signal comprises at least one of a maximum length sequence code, a Gold sequence code and a Kasami sequence code.

4. The method of claim 1 wherein each vibrator has at least two resonance frequencies in a selected frequency band.

5. The method of claim 1 wherein the area of the subsurface comprises a body of water, and wherein an actuation time of each vibrator corresponds to a depth at which each vibrator is operated in the body of water such that the first and at least a second vibrators act as a vibrator array.

6. The method of claim 5 wherein the vibrators each operated at a water depth such that a surface ghost amplifies a downward output of each vibrator within a selected frequency range.

7. The method of claim 1 wherein the modulation operation comprises biphase modulation.

8. A method for subsurface seismic surveying, comprising:

operating a plurality of seismic vibrators each having a different selected frequency response range above an area of the subsurface to be surveyed; and

detecting seismic signals originating from the plurality of vibrators at each of a plurality of seismic receivers disposed at spaced apart locations above the area;

wherein each vibrator is operated by a same direct sequence spread spectrum driver signal;

wherein a different number of modulation operations for each logical value in the driver signal is selected for each vibrator; and

determining seismic energy originating from each of the plurality of vibrators in the detected seismic signals.

9. The method of claim 8 wherein each number of modulation operations is selected to correspond to the frequency response range of each vibrator.

10. The method of claim 8 wherein the direct sequence spread spectrum signal comprises at least one of a maximum length sequence code, a Gold sequence code and a Kasami sequence code.

11. The method of claim 8 wherein each vibrator has at least two resonance frequencies in a selected frequency band.

12. The method of claim 8 wherein the area of the subsurface comprises a body of water, and wherein an actuation time of each vibrator corresponds to a depth at which each vibrator is operated in the body of water such that the first and at least a second vibrators act as a vibrator array.

13. The method of claim 12 wherein the vibrators each operated at a water depth such that a surface ghost amplifies a downward output of each vibrator within a selected frequency range.