Method for treating seismic cubes corresponding to obtained for common zone at different times

1. Method of processing a collection of seismic cubes, each seismic cube corresponding to a gather of seismic traces in which each seismic trace is a time-dependent amplitude signal and is associated with a given position on the ground zone over which the acquisition has been carried out, the various seismic cubes corresponding to one and the same acquisition zone and to various moments of acquisition, characterized in that at least one seismic cube which is an estimate of the component common to at least two seismic cubes corresponding to different moments of acquisition is determined, said estimate of component common to at least two seismic cubes being defined as the coherent or invariant part of the seismic cubes, and this estimate of common component is subtracted from at least one of the two initial cubes.

2. Method according to claim 1 , characterized in that a filtering processing is implemented on a differential cube thus obtained.

3. Method according to claim 1 , characterized in that the cube which corresponds to the estimate of the common component of both of the two initial cubes is subtracted from them, in that a filtering processing is implemented on both of the two differential cubes thus obtained and in that these filtered differential cubes are subtracted or summed to reconstitute an estimate of the difference between the two initial cubes.

4. Method according to claim 1 , characterized in that, to determine a cube which is an estimate of a component common to at least two seismic cubes:

each of these two seismic cubes is converted into the frequency domain to obtain for each of them a real cube and an imaginary cube,

a seismic cube which is an estimate of the component common to the real cubes thus obtained and a cube which is an estimate of the component common to the two imaginary cubes thus obtained are calculated, and

the two cubes, the one real, the other imaginary, thus obtained are converted into the time domain.

5. Method according to claim 1 , characterized in that, to determine a cube which is an estimate of a component common to at least two cubes:

each of these cubes is converted into the frequency domain so as to deduce therefrom for each of them an amplitude cube and a phase cube,

an estimate of the part common to the amplitude cubes thus obtained is calculated.

6. Method according to claim 5 , characterized in that:

the amplitude cube thus obtained is converted into the time domain while associating it respectively with the various phase cubes,

each of the cubes thus obtained in the time domain is converted into the frequency domain so as to obtain for each of these cubes a real cube and an imaginary cube,

a cube which is an estimate of the component common to the real cubes and a cube which is an estimate of the component common to the imaginary cubes are calculated, and the two cubes, the one real, the other imaginary, thus obtained are converted into the time domain.

7. Method according to claim 1 , characterized in that, to determine a cube which is an estimate of a component common to at least two-cubes:

each of these cubes is converted into the frequency domain so as to deduce therefrom for each of them an amplitude cube, as well as a cube corresponding to its real part and a cube corresponding to its imaginary part,

cosines cubes and sine cubes are extracted from the cubes corresponding to the real part and from the cubes corresponding to the imaginary part,

an estimate of the part common to the cosine cubes and an estimate of the sine cubes are calculated,

a common-phase-data cube is deduced from the thus calculated cubes of common parts.

8. Method according to claim 7 , characterized in that:

each of the cubes thus obtained in the time domain is converted into the frequency domain to obtain for each of these cubes a real cube and an imaginary cube,

a cube which is an estimate of the component common to the real cubes and a cube which is an estimate of the component common to the imaginary cubes are calculated, and

the two cubes, the one real, the other imaginary, thus obtained are converted into the time domain.

9. Method according to claim 4 , characterized in that, to calculate a cube which is an estimate of a component common to at least two seismic cubes, a factorial co-kriging processing is implemented.

10. Method according to claim 9 , characterized in that, to calculate a cube which is an estimate of a component common to at least two seismic cubes:

each of these seismic cubes is sampled so as to deduce therefrom for each of them a succession of 2D mappings,

covariance and cross-variance matrices, corresponding to the variograms of both of these two mappings, as well as to their cross-variogram, are determined for each 2D mapping pair thus obtained,

a factorial co-kriging system which corresponds to these matrices is solved so as to deduce therefrom a spatial operator to be applied to the two 2D mappings which correspond thereto, so as to deduce therefrom a 2D mapping which corresponds to their common component, the collection of 2D mappings thus obtained making it possible to reconstitute the common seismic cube.

11. Method according to claim 10 , characterized in that, to determine the co-kriging system to be solved so as to deduce the spatial operator to be applied to two 2D mappings, a mask intended to cancel the data of the said mapping over a certain zone is applied to the data of at least one of the two mappings, prior to the determination of the covariances and of the cross-variances.

12. Method for revealing alterations in geological or geophysical characteristics over hydrocarbon reservoirs, in which seismic acquisitions are implemented at several different moments and seismic cubes corresponding to these acquisitions are processed so as to reveal any alterations, characterized in that said method comprises processing a collection of seismic cubes, each seismic cube corresponding to a gather of seismic traces in which each seismic trace is a time-dependent amplitude signal and is associated with a given position on the ground zone over which the acquisition has been carried out, the various seismic cubes corresponding to one and the same acquisition zone and to various moments of acquisition, characterized in that at least one seismic cube which is an estimate of the component common to at least two seismic cubes corresponding to different moments of acquisition is determined, said estimate of component common to at least two seismic cubes being defined as the coherent or invariant part of the seismic cubes, and this estimate of common component is subtracted from at least one of the two initial cubes.

13. Method according to claim 12 , characterized in that a filtering processing is implemented on a differential cube thus obtained.

14. Method according to claim 12 , characterized in that the cube which corresponds to the estimate of the common component of both of the two initial cubes is subtracted from them, in that a filtering processing is implemented on both of the two differential cubes thus obtained and in that these filtered differential cubes are subtracted or summed to reconstitute an estimate of the difference between the two initial cubes.

15. Method according to claim 12 , characterized in that, to determine a cube which is an estimate of a component common to at least two seismic cubes:

each of these two seismic cubes is converted into the frequency domain to obtain for each of them a real cube and an imaginary cube,

a seismic cube which is an estimate of the component common to the real cubes thus obtained and a cube which is an estimate of the component common to the two imaginary cubes thus obtained are calculated, and

the two cubes, the one real, the other imaginary, thus obtained are converted into the time domain.

16. Method according to claim 12 , characterized in that, to determine a cube which is an estimate of a component common to at least two cubes, each of these cubes is converted into the frequency domain so as to deduce therefrom for each of them an amplitude cube and a phase cube, an estimate of the part common to the amplitude cubes thus obtained is calculated.

17. Method according to claim 16 , characterized in that:

the amplitude cube thus obtained is converted into the time domain while associating it respectively with the various phase cubes,

each of the cubes thus obtained in the time domain is converted into the frequency domain so as to obtain for each of these cubes a real cube and an imaginary cube,

a cube which is an estimate of the component common to the real cubes and a cube which is an estimate of the component common to the imaginary cubes are calculated, and

the two cubes, the one real, the other imaginary, thus obtained are converted into the time domain.

18. Method according to claim 12 , characterized in that, to determine a cube which is an estimate of a component common to at least two cubes:

each of these cubes is converted into the frequency domain so as to deduce therefrom for each of them an amplitude cube, as well as a cube corresponding to the real part and from the cubes corresponding to the imaginary part,

cosines cubes and sine cubes are extracted from the cubes corresponding to the real part and from the cubes corresponding to the imaginary part,

an estimate of the part common to the cosine cubes and an estimate of the sine cubes are calculated, and

a common-phase-data cube is deduced from the thus calculated cubes of common parts.

19. Method according to claim 18 , characterized in that:

each of the cubes thus obtained in the time domain is converted into the frequency domain to obtain for each of these cubes a real cube and an imaginary cube,

a cube which is an estimate of the component common to the real cubes and a cube which is an estimate of the component common to the imaginary cubes are calculated, and

the two cubes, the one real, the other imaginary, thus obtained are converted into the time domain.

20. Method according to claim 15 , characterized in that, to calculate a cube which is an estimate of a component common to at least two seismic cubes, a factorial co-kriging processing is implemented.

21. Method according to claim 20 , characterized in that, to calculate a cube which is an estimate of a component common to at least two seismic cubes:

each of these seismic cubes is sampled so as to deduce therefrom for each of them a succession of 2D mappings,

covariance and cross-variance matrices, corresponding to the variograms of both of these two mappings, as well as to their cross-variogram, are determined for each 2D mapping pair thus obtained,

a factorial co-kriging system which corresponds to these matrices is solved so as to deduce therefrom a spatial operator to be applied to the two 2D mappings which correspond thereto, so as to deduce therefrom a 2D mapping which corresponds to their common component, the collection of 2D mappings thus obtained making it possible to reconstitute the common seismic cube.

22. Method according to claim 21 , characterized in that, to determine the co-kriging system to be solved so as to deduce the spatial operator to be applied to two 2D mappings, a mask intended to cancel the data of the said mapping over a certain zone is applied to the data of at least one of the two mappings, prior to the determination of the covariances and of the cross-variances.