Method for seismic processing, in particular for compensating birefringence on seismic traces

• US 20050013195A1
• Filed: 11/07/2002
• Published: 01/20/2005
• Est. Priority Date: 11/08/2001
• Status: Active Grant

• Current Assignee: Cggveritas Services SA (CGG)
• Original Assignee: Cggveritas Services SA (CGG)
• Inventors: Garotta, Robert
• Granted Patent: US 7,436,735 B2
• Time in Patent Office: Days
• US Class Current: 367/38
• CPC Class Codes: G01V 1/28 Processing seismic data, e.g. for interpretation or for event detection G01V1/48 takes precedence
• CPC Class Codes: G01V 2210/58 Media-related

Abstract

The invention relates to a method of seismic processing for obtaining information on the geophysics of the subsoil, the method comprising the following steps: a) acquiring seismic traces at at least one point on the surface of the subsoil or in the subsoil, the seismic traces corresponding on each occasion to two perpendicular components of a shear wave emitted into the subsoil and reflected by different interfaces therein; b) applying a succession of transformations (⊥) at least to a temporal portion of the traces, which transformations are the inverses of the transformations that it is assumed that the wave has encountered on passing through a succession of layers in the subsoil, this operation being repeated for different assumptions concerning birefringence in the various layers; c) for each of these assumptions, determining the value of a parameter representative of the coherence/similarity between the result traces obtained in this way; and d) selecting as a function of the values obtained in this way that one of the hypotheses which is considered as being most representative of the subsoil, the two result traces obtained for said hypothesis being compensated traces of the subsoil birefringency.

Claims

1. / A method of seismic processing for obtaining information on the geophysics of the subsoil, the method comprising the following steps:

a) acquiring seismic traces at at least one point on the surface of the subsoil or in the subsoil, the seismic traces corresponding on each occasion to two perpendicular components of a shear wave emitted into the subsoil and reflected by different interfaces therein;

b) applying a succession of transformations (⊥

) at least to a temporal portion of the traces, which transformations are the inverses of the transformations that it is assumed that the wave has encountered on passing through a succession of layers in the subsoil, this operation being repeated for different assumptions concerning birefringence in the various layers;

c) for each of these assumptions, determining the value of a parameter representative of the coherence/similarity between the result traces obtained in this way; and

d) selecting as a function of the values obtained in this way that one of the hypotheses which is considered as being most representative of the subsoil, the two result traces obtained for said hypothesis being compensated traces of the subsoil birefringency.

2. / A method according to claim 1, characterized in that a hypothesis concerning the birefringency of a layer is characterized by at least one parameter relating to the orientation of the birefringency axes and by at least one parameter relating to the delay imparted by said layer between propagation oriented on the fast axis and propagation oriented on the slow axis, and in that the results are represented or displayed in two dimensions or in three dimensions with, for different portions of the traces, successions of values corresponding to the values of said parameters for a succession of layers through which the wave has passed and to the selected assumption concerning birefringency.

3. / A method according to claim 2, characterized in that comparison attributes are determined on the result traces and represented or displayed together with the values of the orientation and delay parameters.

4. / A method according to claim 1, characterized in that in order to select a birefringency assumption that is considered as being the most representative, the value of the parameter representing coherence/similarity of the result traces obtained for each hypothesis is compared with a threshold value.

5. / A method according to claim 1, characterized in that successive iterations are performed during which a new birefringency assumption is selected for each operation as a function of the value calculated at the preceding iteration for the parameter representative of coherence/similarity between the result traces obtained, and in that in order to select the birefringency assumption that is considered as being the most representative, it is determined whether the value obtained for the parameter representative of coherence/similarity between the result traces at the iteration in question lies within a given proximity range relative to the values obtained for the same parameter during preceding iterations.

6. / A method according to claim 1, characterized in that it is implemented on trace portions having a duration of the order of 100 milliseconds or longer.

7. / A method according to claim 6, characterized in that the trace portions are sampled with a sampling time of the order of 2 or 4 milliseconds or shorter, each of the sampling intervals or groups of successive intervals corresponding to a layer under study.

8. / A seismic processing method for revealing fractures in the subsoil, comprising the steps of:

a) acquiring seismic traces at at least one point on the surface of the subsoil or in the subsoil, the seismic traces corresponding on each occasion to two perpendicular components of a shear wave emitted into the subsoil and reflected by different interfaces therein;

b) applying a succession of transformations (⊥

) at least to a temporal portion of the traces, which transformations are the inverses of the transformations that it is assumed that the wave has encountered on passing through a succession of layers in the subsoil, this operation being repeated for different assumptions concerning birefringence in the various layers;

c) for each of these assumptions, determining the value of a parameter representative of the coherence/similarity between the result traces obtained in this way; and

d) selecting as a function of the values obtained in this way that one of the hypotheses which is considered as being most representative of the subsoil, the two result traces obtained for said hypothesis being compensated traces of the subsoil birefringency.