Detection of ground roll cone

• US 6,266,620 B1
• Filed: 05/10/1999
• Issued: 07/24/2001
• Est. Priority Date: 11/15/1996
• Status: Expired due to Fees

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Lemenager, Erwann, Baeten, Guido Jozef Maria
• Primary Examiner(s): Oda, Christine
• Assistant Examiner(s): Taylor, Victor J.
• Application Number:
  US09/297,879
• Time in Patent Office: 806 Days
• Field of Search: 702/17, 702/14, 367/69, 367/72
• US Class Current: 702/17
• CPC Class Codes: G01V 1/288 Event detection in seismic signals, e.g. microseismics G01V1/36 takes precedence
• CPC Class Codes: G01V 1/36 Effecting static or dynamic corrections on records, e.g. correcting spread; Correlating seismic signals; Eliminating effects of unwanted energy
• CPC Class Codes: G01V 2210/21 Frequency-domain filtering, e.g. band pass
• CPC Class Codes: G01V 2210/52 Move-out correction

Abstract

The present invention relates to a method to detect areas of acquired seismic data that contain ground roll. The method according to the invention allows the detection of ground roll cone on the basis of an estimate of the local ground roll velocity or even without any knowledge of the ground roll velocity. The method according to the invention is further more very useful for an automatic process of ground roll detection.

Claims

1. A method of automatically detecting a ground roll cone in seismic data, the method comprising the following steps:

(a) in respect to one receiver station, where the output data resulting from one shot is gathered from several geophones, selecting a trace of seismic raw data from a first geophone;

(b) determining in the data trace of the first geophone data blocks in form of time windows where signal amplitude/energy lies above a predefined reference level;

(c) merging together adjacent data blocks determined in step (b) and suppressing very small data blocks identified in step (b);

(d) repeating the process with the data from the other geophones, and then calculating for each set of two adjacent traces that were obtained according to step (c) a ratio between average velocity and differential velocity in each selected data block by process of cross-correlation in order to discriminate between various types of seismic energy on the basis of their move-out;

(e) comparing the ratios between average velocity and differential velocity determined in step (d) with a predefined favorable ratio between average velocity and differential velocity and identifying a data block with a most favorable ratio; and

(f) by evaluating amplitude behavior near the edges of the selected data block of step (e), extending this data block such that it includes all relevant and dominant ground roll energy.

2. A method according to claim 1, further including the step of filtering out data with a velocity below a reference velocity between steps (a) and (b).

3. A method according to claim 1, further including the step of applying a band-pass filter to the data between steps (a) and (b).

4. A method according to claim 1, further including the step of applying a time-variant amplitude correction to the data between steps (a) and (b).

5. A method according to claim 1, further including the step of performing an NMO correction of the data between steps (a) and (b).

6. A method according to claim 1, further including the step of:

(g) similarly determining the ground roll containing data blocks in the data traces from the other geophones of the receiver station.

7. A method according to claim 6, further including the step of:

(h) repeating the process for data traces for the same shot and gathered at other receiver stations in order to obtain other ground roll velocity estimates, and determining therefrom a minimum and maximum ground roll velocity that define the ground roll cone.

8. A method of determining the ground roll cone in seismic data, the method comprising the following steps:

(a) in respect to one receiver station, where output data resulting from one shot is gathered from several geophones, selecting a trace of seismic raw data from a first geophone;

(b) determining in the data trace of the first geophone data blocks in the form of time windows where signal amplitude/energy lies above a predefined reference level;

(c) merging together adjacent data blocks determined in step (b) and suppressing very small data blocks identified in step (b);

(d) calculating for each selected data block according to step (c) an average velocity, and comparing such average velocities with a reference average velocity, and identifying a particular data block with an average velocity that is closest to the reference average velocity; and

(e) by evaluating amplitude behavior near the edges of the selected data block of step (d), extending this data block such that it includes all relevant and dominant ground roll energy.

9. A method of claim 8, further including the step of filtering out data with a velocity below a reference velocity between steps (a) and (b).

10. A method of claim 8, further including the step of applying a band-pass filter to the data between steps (a) and (b).

11. A method of claim 8, further including the step of applying a time-variant amplitude correction to the data between steps (a) and (b).

12. A method of claim 8, further including the step of:

(f) similarly determining the ground roll containing data blocks in the data traces from the other geophones of the receiver station.

13. A method of claim 12, further including the step of:

(g) repeating the process for data traces for the same shot and gathered at other receiver stations in order to obtain other ground roll velocity estimates, and determining therefrom a minimum and maximum ground roll velocity that define the ground roll cone.

14. A method according to claim 10, wherein the band-pass filter has a pass band of 10 to 30 Hz.

15. A method according to claim 9, wherein the reference velocity used is of the order of the shear wave velocity of the deepest layer of interest.

16. A method according to claim 15, wherein the reference velocity is selected such that the large-amplitude first-arrivals in the data trace are filtered out.

17. A method according to claim 10, wherein the band-pass filter is implemented as a Quadrature Mirror Filter.

18. A method according to claim 8, wherein before step (c) is performed, previous steps (a) and (b) are applied to a raw data trace of at least a second geophone connected to the same receiver station, and then data blocks are selected, according to step (b), that are common for all data traces.

19. A method according to claim 13, wherein a median filter is used for obtaining minimum and maximum ground roll velocity that define the ground roll cone.

20. A method of determining the ground roll cone in seismic data, the method comprising the following steps:

(a) selecting a trace of seismic data from a first geophone;

(b) determining in the data trace of the first geophone data blocks in the form of time windows where signal amplitude/energy lies above a reference level;

(c) merging together adjacent data blocks determined in step (b) and suppressing very small data block identified in step (b);

(d) calculating for each selected data block according to step (c) an average velocity, and comparing such average velocities with a reference average velocity, and identifying a particular data block with an average velocity closest to the reference average velocity; and

(e) determining a minimum and maximum ground roll velocity that define the ground roll cone utilizing said identified data block.