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

• US 7,684,281 B2
• Filed: 04/14/2008
• Issued: 03/23/2010
• Est. Priority Date: 03/03/2004
• Status: Active Grant

• Current Assignee: PGS Americas, Inc. (PGS ASA)
• Original Assignee: PGS Americas, Inc. (PGS ASA)
• Inventors: Borresen, Claes Nicolai, Vaage, Svein Torleif, Tenghamn, Stig Rune Lennart
• Primary Examiner(s): Keith; Jack W.
• Assistant Examiner(s): Hughes; Scott A
• Application Number:
  US12/082,804
• Publication Number:
  US 20080192571A1
• Time in Patent Office: 708 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 a seismic wavefield. At least a part of the particle motion sensor signal is calculated from a recorded pressure signal and the calculated at least a part of the particle motion sensor signal is used to generate a particle motion sensor signal in which noise is substantially attenuated in at least a lower frequency range thereof. The pressure sensor data and the noise attenuated particle motion sensor signal can then be combined to calculate up- and down-going wavefields.

Claims

1. A method for combining recorded signals of a pressure sensor and a particle motion sensor located in a towed marine seismic streamer to improve signal to streamer vibration noise ratio in the particle motion sensor signal, comprising:

converting seismic signals recorded in the towed marine seismic streamer into a particle motion sensor signal, the seismic signals representative of characteristics of subsurface earth formations and acquired by deployment of a plurality of pressure sensors and particle motion sensors overlying an area of the earth'"'"'s subsurface to be evaluated, the sensors generating at least one of an electrical and optical signal in response to seismic energy, by the following;

calculating at least a portion of a particle motion sensor signal from the recorded pressure sensor signal; and

merging the calculated at least a portion of the particle motion sensor signal with the recorded particle motion sensor signal to generate a particle motion sensor signal in which signal to streamer vibration noise ratio is substantially improved in at least a lower frequency range thereof, useful for imaging the earth'"'"'s subsurface.

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 particle 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 sensor 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 effects of differences in incident angle in frequency-wave number domain, (f, k_x, k_y).

11. The method of claim 1, wherein the recorded particle motion signal involving a single streamer is compensated for effects of differences in incident angle in frequency-wave number domain, (f, k_y), keeping the wave number in 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 effects of differences in incident angle in frequency domain, (f), keeping wave numbers in x and y directions, k_x and k_y, respectively, constant for each sensor.

13. The method of claim 1, wherein the at least a portion of the particle motion signal G_calculated(F, k) is calculated 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 f is frequency, k=(k_x, k_y) is a wave number with k_x a wave number in an x direction and k_y a wave number in a y direction, c is reflection coefficient at sea surface and τ

is time delay between a direct arrival and a surface reflection.

14. The method of claim 13, wherein the time delay r 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 depth of the pressure sensors and particle motion sensors and ν

is velocity of sound in the water.

15. The method of claim 13, wherein the merging is done with tapering of the signals in an overlapping frequency interval.

16. The method of claim 15, wherein the tapering of the signals is carried out by merging the amplitude and the phase spectra separately.

17. The method of claim 13, wherein the at least a portion of the particle motion signal G_calculated(f,k_x,k_y) is calculated in the frequency-wave number domain, (f,k_x,k_y, from a recorded pressure signal H_signal(f,k_x,k_y) involving data from a plurality of streamers by

$G_{\mathrm{calculated}}$

( f , k x , k y ) = H signal ⁡

( f , k x , k y ) ·

1 - c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) 1 + c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) .

18. The method of claim 13, wherein the at least a portion of the particle motion signal G_calculated(f,k_x) is calculated in the frequency-wave number domain, (f,k_y) from a recorded pressure signal H_signal(f,k_y) involving data from a single streamer by

$G_{\mathrm{calculated}}$

( f , k x ) = H signal ⁡

( f , k x ) ·

1 - c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) 1 + c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) ,

where k_y is kept constant for each streamer.

19. The method of claim 13, wherein the at least a portion of the particle motion signal G_calculated(f) is calculated in the frequency (f) domain from a recorded pressure signal H_signal(f) involving data from a single sensor or group of sensors by

$G_{\mathrm{calculated}}$

( f , ) = H signal ⁡

( f ) ·

1 - c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) 1 + c ·

exp ⁡

( - ⅈ

2π

⁢

⁢

f ⁢

⁢

τ

) ,

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

20. The method of claim 1, wherein the recorded pressure signal and the particle motion signal in which signal-to-streamer vibration noise is substantially improved are combined to calculate total up- and down-going wavefields.