System for combining signals of pressure sensors and particle motion sensors in marine seismic streamers

• US 7,359,283 B2
• Filed: 03/03/2004
• Issued: 04/15/2008
• Est. Priority Date: 03/03/2004
• Status: Active Grant

• Current Assignee: PGS Americas, Inc. (PGS ASA)
• Original Assignee: PGS Americas, Inc. (PGS ASA)
• Inventors: Tenghamn, Stig Rune Lennart, Borresen, Claes Nicolai, Vaage, Svein Torleif
• Primary Examiner(s): Keith; Jack W.
• Assistant Examiner(s): Hughes; Scott A
• Application Number:
  US10/792,510
• Publication Number:
  US 20050195686A1
• Time in Patent Office: 1,504 Days
• Field of Search: 367/15, 367/21, 367/24
• US Class Current: 367/24
• CPC Class Codes: G01V 1/3808 Seismic data acquisition, e.g. survey design

Abstract

Signals of pressure sensors and particle motion sensors located in marine seismic streamers are combined to generate pressure sensor data and particle motion data with substantially the same broad bandwidth. The noisy low frequency part of the motion signals are calculated from the recorded pressure signals and merged with the non-noisy motion signals. The two broad bandwidth data sets can then be combined to calculate the full up- and down-going wavefields.

Claims

1. A method for combining signals of a pressure sensor and a particle motion sensor recorded in a marine seismic streamer to reduce noise in the combined pressure sensor signal and particle motion sensor signal, the recorded pressure signal having a bandwidth comprising a first frequency range and a second frequency range, the first frequency range being at lower frequencies than the frequencies of the second frequency range, and the recorded particle motion sensor signal having a bandwidth comprising at least the second frequency range, comprising:

calculating a particle motion sensor signal in the first frequency range from the recorded pressure sensor signal, thereby generating a simulated particle motion sensor signal in the first frequency range;

merging the simulated particle motion sensor signal only in the first frequency range with the recorded particle motion sensor signal in the second frequency range to generate a merged particle motion sensor signal having substantially the same bandwidth as the bandwidth of the recorded pressure sensor signal; and

combining the recorded presssure sensor signal and the merged particle motion sensor signal for further processing.

2. The method of claim 1, wherein the pressure sensors comprise hydrophones.

3. The method of claim 1, wherein the particle motion sensors comprise geophones.

4. The method of claim 1, wherein the particle motion sensors comprise accelerometers.

5. The method of claim 1, wherein the particle motion sensors comprise sensors which can measure more than one particle motion wavefield component.

6. The method of claim 1, wherein the particle motion sensors and the pressure sensors are co-located.

7. The method of claim 1, wherein the parlicle motion sensors and the pressure sensors are located so that recorded signals from the sensors can be used to calculate corresponding data sets at substantially the same location.

8. The method of claim 1, wherein the recorded pressure sensor signal and the recorded particle motion signal are corrected for relative differences in instrument impulse response.

9. The method of claim 1, wherein relative amplitudes of the recorded pressure sensor signal and the recorded particle motion signal are corrected for relative differences in amplitudes of pressure and particle motion.

10. The method of claim 1, wherein the recorded particle motion signal involving a plurality of streamers, is compensated for the effect of differences in incident angle in the frequency-wave number domain, (ƒ

, k_x, k_y).

11. The method of claim 1, wherein the recorded particle motion signal involving a single streamer is compensated for the effect of differences in incident angle in the frequency-wave number domain, (ƒ

, k_x), keeping the wave number in the y direction k_y constant for each streamer.

12. The method of claim 1, wherein the recorded particle motion signal involving a single sensor or group of sensors is compensated for the effect of differences in incident angle in the frequency domain, (ƒ

), keeping wave numbers in the x and y directions, k_x and k_y, respectively, constant for each sensor.

13. The method of claim 1, wherein a low frequency part of the simulated particle motion signal G_calculated(f, k) is calculatecl in the frequency-wave number domain, from a recorded pressure signal H_signal(f, k) by

$G_{\mathrm{calculated}}$

( f , k _ ) = H signal ⁡

( f , k _ ) ·

1 - c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) 1 + c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) ,

where ƒ

is the frequency, k=(k_x, k_y) is the wave number with k_x, the wave number in the x direction and k_y the wave number in the y direction, c is the reflection coefficient at the sea surface and τ

is the time delay between a direct arrival and a sulrface reflection.

14. The method of claim 13, wherein the time delay τ

is given by the following equation;

$\mathrm{\tau <br><br>}=\frac{2·<br><br>D·<br><br>\sqrt{1-\frac{v^2·<br><br>{<br><br>k<br><br>}^2}{f^2}}}{v},$

where D is the depth of the pressure sensors and particle motiion sensors and ν

is the velocity of sound in the water.

15. The method of claim 13, wherein the simulated particle motion signal is merged with the recorded particle motion signa1 to produce a high signal-to-noise broad bandwidth particle motion signal.

16. The method of claim 15, wherein the merging is done with tapering of the signals in an overlapping frequency interval.

17. The method of claim 16, wherein the tapering of the signals is carried out by merging the amplitude and the phase spectra separately.

18. The method of claim 13, wherein the low frequency part of the simulated particle motion signal G_calculated(f, k_x, k_y) is calculated in the frequency-wave number domain, (ƒ

, k_x, k_y) from the recorded pressure signal H_signal(ƒ

, k_x, k_y) involving data from a plurality of streamers by

$G_{\mathrm{calculated}}<br><br>\left(f,k_x,k_y\right)=H_{\mathrm{signal}}<br><br>\left(f,k_x,k_y\right)·<br><br>\frac{1-c·<br><br>\exp <br><br>\left(-\mathrm{i<br><br>2\pi <br><br>}<br><br><br><br>f<br><br><br><br>\mathrm{\tau <br><br>}\right)}{1+c·<br><br>\exp <br><br>\left(-\mathrm{i<br><br>2\pi <br><br>}<br><br><br><br>f<br><br><br><br>\mathrm{\tau <br><br>}\right)}.$

19. The method of claim 13, wherein the low frequency part of the simulated particle motion signal G_calculated(f, k_x) is calculated in the frequency-wave number domain, (ƒ

, k_x) from a recorded pressure signal H_signal(f,k_x) involving data from a single streamer by

$G_{\mathrm{calculated}}<br><br>\left(f,k_x\right)=H_{\mathrm{signal}}<br><br>\left(f,k_x\right)·<br><br>\frac{1-c·<br><br>\exp <br><br>\left(-\mathrm{i<br><br>2\pi <br><br>}<br><br><br><br>f<br><br><br><br>\mathrm{\tau <br><br>}\right)}{1+c·<br><br>\exp <br><br>\left(-\mathrm{i<br><br>2\pi <br><br>}<br><br><br><br>f<br><br><br><br>\mathrm{\tau <br><br>}\right)},$

where k_y is kept constant for each streamer.

20. The method of claim 13, wherein the low frequency part of the simulated particle motion signal G_calculated(f) is calculated in the frequency (ƒ

) domain from a recorded pressure signal H_signal(f) involving data from a single sensor or group of sensors by

$G_{\mathrm{calculated}}<br><br>\left(f,\right)=H_{\mathrm{signal}}<br><br>\left(f\right)·<br><br>\frac{1-c·<br><br>\exp <br><br>\left(-\mathrm{i<br><br>2\pi <br><br>}<br><br><br><br>f<br><br><br><br>\mathrm{\tau <br><br>}\right)}{1+c·<br><br>\exp <br><br>\left(-\mathrm{i<br><br>2\pi <br><br>}<br><br><br><br>f<br><br><br><br>\mathrm{\tau <br><br>}\right)},$

where k_x is kept constant for each sensor and k_y is kept constant for each sensor.

21. The methold of claim 1, wherein the recorded pressure signal and the merged particle motion signal with substantially the same bandwidth are combined to calculate the total up- and down-going wavefields.

22. The method of claim 1, wherein the first frequency range comprises low frequencies within the bandwidth of the recorded pressure sensor signal.

23. The method of claim 1, wherein the first frequency range is a frequency range in which the particle motion sensor signal has a low signal-to-noise ratio.