Device and method for determining S-wave attenuation in near-surface condition

Patent metadata

Field	Value
Publication number	US-9291733-B2
Application number	US-201213353587-A
Country	US
Kind code	B2
Filing date	Jan 19, 2012
Priority date	Jan 31, 2011
Publication date	Mar 22, 2016
Grant date	Mar 22, 2016

Abstract

Computing device and method for determining primary and ghost components from S-waves recorded in near-surface conditions, wherein the S-waves are refracted or reflected from a structure in a subsurface. The method includes a step of receiving seismic data (R, V) with regard to the S-waves, wherein the seismic data includes vertical and radial components recorded with a buried three-component receiver; a step of calculating with a processor a primary component (P) and a ghost component (G) from the vertical and radial components; and a step of computing an image of a subsurface based on the primary and ghost components (P, G). The S-waves form a plane wave.

First claim

What is claimed is:

1. A method for determining primary and ghost components from S-waves recorded in near-surface conditions, the method comprising:
receiving seismic data (R, V) with regard to the S-waves, wherein the seismic data includes vertical and radial components recorded with a buried three-component receiver;
calculating with a processor a primary component (P) and a ghost component (G) from the vertical and radial components corresponding to the S-waves; and
computing an image of a subsurface based on the primary and ghost components (P, G),
wherein the S-waves form a plane wave.

2. The method of claim 1 , wherein the near-surface conditions describe properties of the ground located above the buried three-dimensional receiver.

3. The method of claim 1 , wherein the S-waves are refracted from a structure in the subsurface.

4. The method of claim 1 , further comprising:
computing a Q-factor of the S-waves in the near-surface by using a modified log-spectral ratio algorithm that relies on the primary and ghost components.

5. The method of claim 4 , wherein the computing step further comprises:
determining a gradient γ of a log-spectral ratio between the primary and ghost components.

6. The method of claim 5 , further comprising:
plotting a logarithm of a ratio between the primary and ghost components versus a frequency of the components to determine the gradient γ.

7. The method of claim 5 , further comprising:
calculating a near-surface speed V s of the S-waves by,
selecting two S-waves, a first S-wave that is recorded by the buried three-component receiver when the first S-wave propagates towards the surface of the earth, and a second S-wave that is recorded by the buried three-component receiver after the second S-wave has reflected from the surface of the earth and is traveling away from it,
calculating a geometrical distance travelled by the second S-wave between a time when the first S-wave is recorded and a time when the second S-wave is recorded,
cross-correlating data related to the first and second S-waves to determine a travel time, and
dividing the geometrical distance by the travel time to determine the near-surface speed.

8. The method of claim 7 , further comprising:
calculating a distance r travelled by the second S-wave between (1) a point lying on an imaginary line that extends through buried three-dimensional receivers, wherein the imaginary line intersects with the second S-wave at the point, and (2) a position of the three-dimensional receiver that records the first S-wave.

9. The method of claim 8 , further comprising:
calculating the Q factor as a ratio of (i) r and (ii) the product of Vs and γ.

10. The method of claim 1 , further comprising:
considering that an amplitude of a first, refracted, up-going S-wave, at a point between two consecutive, buried, three-dimensional receivers, is the same as an amplitude of a second, refracted, up-going S-wave that is recorded by one of the two consecutive, buried, three-dimensional receivers.

11. A computing device for determining primary and ghost components from S-waves recorded in near-surface conditions, the computing device comprising:
an interface configured to receive seismic data with regard to the S-waves, wherein the seismic data includes vertical and radial components recorded with a buried three-component receiver; and
a processor connected to the interface and configured to,
calculate a primary component and a ghost component from the vertical and radial components corresponding to the S-waves; and
compute an image of a subsurface based on the primary and ghost components,
wherein the S-waves form a plane wave.

12. The computing device of claim 11 , wherein the near-surface conditions describe properties of the ground located above the buried three-dimensional receiver.

13. The computing device of claim 11 , wherein the S-waves are refracted from a structure in the subsurface.

14. The computing device of claim 11 , wherein the processor is further configured to:
compute a Q-factor of the S-waves in the near-surface by using a modified log-spectral ratio algorithm that relies on the primary and ghost components.

15. The computing device of claim 14 , wherein the processor is further configured to:
determine a gradient γ of a log-spectral ratio between the primary and ghost components;
plot a logarithm of a ratio between the primary and ghost amplitude components versus a frequency of the components to determine the gradient γ;
calculate a near-surface speed V s of the S-waves by,
selecting two S-waves, a first S-wave that is recorded by the buried three-component receiver when the first S-wave propagates towards the surface of the earth, and a second S-wave that is recorded by the buried three-component receiver after the second S-wave has reflected from the surface of the earth and is traveling away from it,
calculating a geometrical distance travelled by the second S-wave after the first S-wave is recorded and before the second S-wave is reflected,
cross-correlating data related to the first and second S-waves to determine a travel time, and
dividing the geometrical distance by the travel time to determine the near-surface speed;

calculate a distance r travelled by the second S-wave between (1) a point lying on an imaginary line that extends through buried three-dimensional receivers, wherein the imaginary line intersects with the second S-wave at the point, and (2) a position of the three-dimensional receiver that records the first S-wave; and
calculate the Q factor as a ratio of (i) r and (ii) the product of Vs and γ.

16. The computing device of claim 15 , wherein the processor is further configured to:
consider that an amplitude of a first up-going S-wave, at a point between two consecutive, buried, three-dimensional receivers, is the same with an amplitude of a second up-going S-wave that is recorded by one of the two consecutive, buried, three-dimensional receivers.

17. A method for determining primary and ghost components from S-waves recorded in near-surface conditions, the method comprising:
receiving seismic data with regard to the S-waves, wherein the seismic data includes vertical and radial components recorded with a buried three-component receiver;
calculating with a processor a primary component and a ghost component from the vertical and radial components corresponding to the S-waves; and
computing an image of a subsurface based on the primary and ghost components,
wherein the S-waves form a plane wave, and
the near-surface conditions describe a part of the subsurface between the buried three-dimensional receiver and a surface of the earth.

18. The method of claim 17 , further comprising:
generating the S-waves with a source located below a reservoir of interest in the subsurface, part of the S-waves propagating downwards in the subsurface; and
refracting and not reflecting the S-waves propagating downwards in the subsurface to produce the recorded S-waves.

19. The method of claim 17 , wherein the primary component P is given by

P
=

1

sin
⁡

(

2
⁢
θ

)

Assignees

• De Meersman Kristof
• Cggveritas Services Sa

Inventors

• De Meersman Kristof

Classifications

• G01V1/28 Primary

  Processing seismic data, e.g. for interpretation or for event detection (G01V1/48 takes precedence) · CPC title

• G01V2210/612

  Previously recorded data, e.g. time-lapse or 4D · CPC title

• G01V2210/56

  De-ghosting; Reverberation compensation · CPC title