Method and system for selecting parameters of a seismic source array

Patent metadata

Field	Value
Publication number	US-9645265-B2
Application number	US-201313957285-A
Country	US
Kind code	B2
Filing date	Aug 1, 2013
Priority date	Dec 19, 2007
Publication date	May 9, 2017
Grant date	May 9, 2017

Abstract

A method for selecting parameters of a seismic source array comprising a plurality of source elements each having a notional source spectrum is described, the method comprising calculating a ghost response function of the array; calculating directivity effects of the array; and adjusting the parameters of the array such that the directivity effects of the array are compensated by the ghost response to minimize angular variation of a far field response in a predetermined frequency range. A method for determining a phase center of a seismic source array is also related, the method comprising calculating a far field spectrum of the array at predetermined spherical angles, and minimizing the phase difference between the farfield spectra within a predetermined frequency range by adjusting a vertical reference position from which the spherical angles are defined.

First claim

The invention claimed is:

1. A method for selecting parameters of a seismic source array comprising a plurality of source elements each having a notional source spectrum, the method comprising:
calculating a ghost response function of the array;
calculating an aperture smoothing function of the array;
adjusting the parameters of the array such that the aperture smoothing function of the array at least partially offsets the ghost response in a predetermined frequency range;
calculating a far field spectrum of the array having the adjusted parameters; and
determining a phase center of the array.

2. The method of claim 1 , wherein the array comprises a plurality of layers, each layer comprising a plurality of source elements having substantially the same depth.

3. The method of claim 2 , wherein a depth ratio of the layers is selected such that a first notch in the ghost response is above the predetermined frequency range.

4. The method of claim 3 , wherein the array comprises two layers of source elements and the depth ratio of the two layers is in the range 0.25 to 0.6.

5. The method of claim 4 , wherein the depth ratio of the two layers is in the range 0.3 to 0.5.

6. The method of claim 2 , wherein a minimum wavelength of the predetermined frequency range is greater than 4/3 of a maximum source element depth.

7. The method of claim 2 , wherein a minimum wavelength of the predetermined frequency range is greater than two times a maximum source element depth.

8. The method of claim 2 , where the notional source spectra of the elements at each depth layer are substantially identical.

9. The method of claim 2 , wherein a length to depth ratio of each layer is less than 2.

10. The method of claim 1 , wherein the array comprises a single layer of source elements at a common depth, and the parameters comprise a length to depth ratio of the array.

11. The method of claim 10 , wherein the length to depth ratio is in the range 1.5 to 3.

12. The method of claim 1 , wherein depths of the source elements are selected such that a first notch in the ghost response is above the predetermined frequency range.

13. The method of claim 1 , wherein the source elements are arranged to substantially form a vertical line array.

14. The method of claim 1 , wherein all of the notional source spectra are substantially identical.

15. The method of claim 1 , wherein positions of the source elements have rotational symmetry in azimuth of order three or greater in a horizontal plane.

16. The method of claim 1 , wherein angular variation is minimized within a range of take-off angles of 0 to 40 degrees.

17. The method of claim 1 , wherein the predetermined frequency range is in the range of 0 to 150 Hz.

18. A method for determining a phase center of a seismic source array, the method comprising:
calculating a far field spectrum of seismic source array at predetermined spherical angles, the calculating including calculating an aperture smoothing function, calculating a ghost response function and calculating the far field spectrum based on a combination of the aperture smoothing function and the ghost response function; and
reducing a phase difference between the calculated far field spectrum within a predetermined frequency range by adjusting a vertical reference position from which the spherical angles are defined.

19. The method of claim 18 , wherein the array comprises two layers of the source elements and a depth ratio of the two layers is in the range 0.25 to 0.6.

20. The method of claim 19 , wherein the depth ratio of the two layers is in the range 0.3 to 0.5.

21. The method of claim 18 , wherein angular phase variation is minimized within a range of take-off angles of 0 to 40 degrees.

22. The method of claim 18 , wherein the predetermined frequency range is in the range of 0 to 150 Hz.

23. The method of claim 18 , wherein
the array comprises a plurality of layers, each layer comprising a plurality of source elements having substantially the same depth, and
the source elements in each layer are configured to fire with a synchronization time delay to align vertically downgoing wavefields.

24. The method of claim 18 , further comprising processing seismic data collected from the array.

Assignees

• Westerngeco Llc
• Westerngeco Llc

Inventors

• Hopperstad Jon-Fredrik
• Laws Robert Montgomery
• Kragh Julian Edward

Classifications

• G01V1/137

  which fluid escapes from the generator in a pulsating manner, e.g. for generating bursts {, airguns} · CPC title

• G01V1/38 Primary

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

• G01V1/133

  using fluidic driving means, e.g. highly pressurised fluids; {using implosion}(G01V1/104 takes precedence) · CPC title

• G01V1/3861

  control of source arrays, e.g. for far field control · CPC title

• G01V1/053

  for generating transverse waves · CPC title