Processing simultaneous vibratory seismic data

• US 6,766,256 B2
• Filed: 10/23/2002
• Issued: 07/20/2004
• Est. Priority Date: 02/15/2000
• Status: Active Grant

• Current Assignee: WesternGeco LLC
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Jeffryes, Benjamin Peter
• Primary Examiner(s): MCELHENY JR, DONALD E
• Application Number:
  US10/203,435
• Publication Number:
  US 20030093224A1
• Time in Patent Office: 636 Days
• Field of Search: 702/14, 702/17, 367/43, 367/45, 367/46
• US Class Current: 702/17
• CPC Class Codes: G01V 1/005 with exploration systems emitting special signals, e.g. frequency swept signals, pulse sequences or slip sweep arrangements
• CPC Class Codes: G01V 1/364 Seismic filtering G01V1/37 takes precedence
• CPC Class Codes: G01V 1/37 specially adapted for seismic systems using continuous agitation of the ground , e.g. using pulse compression of frequency swept signals for enhancement of received signals
• CPC Class Codes: G01V 2210/20 Trace signal pre-filtering to select, remove or transform specific events or signal components, i.e. trace-in/trace-out removing noise G01V2210/32
• CPC Class Codes: G01V 2210/32 Noise reduction

Abstract

A method of processing seismic data, said seismic data having been obtained by: performing a plurality of sweeps, wherein each sweep comprises generating seismic signals in the earth using a plurality of vibrators by applying a pilot sweep wave-form to each vibrator, each pilot sweep being a waveform of changing frequency; measuring the force applied to the earth by each vibrator to determine a measured force waveform; and measuring the seismic signals at one or more locations remote from the vibrators; said method comprising: filtering the measured force waveform to remove harmonics of the pilot sweep and thus determining a filtered force waveform; generating an inversion operator from the filtered force waveform for each vibrator; and applying said inversion operator to the measured seismic signals to determine the contribution of each vibrator to the seismic signals.

Claims

1. A method of processing seismic data, said seismic data having been obtained by steps comprising:

performing a plurality of sweeps, wherein each sweep comprises generating seismic signals in the earth using a plurality of vibrators by applying a pilot sweep waveform to each vibrator, each pilot sweep being a waveform of changing frequency;

measuring the force applied to the earth by each vibrator to determine a measured force waveform; and

measuring the seismic signals at one or more locations remote from the vibrators;

filtering the measured force waveform to remove harmonics of the pilot sweep from the measured force waveform and thus determining a filtered force waveform;

generating an inversion operator from the filtered force waveform for each vibrator; and

applying said inversion operator to the measured seismic signals to determine the contribution of each vibrator to the seismic signals.

2. A method as claimed in claim 1, wherein the step of measuring the force applied to the earth is performed using signals from accelerometers on the vibrator in combination with the pilot sweep.

3. A method as claimed in claim 1, wherein the measured force waveform is filtered using a time varying notch filter.

4. A method as claimed in claim 1, wherein the measured force waveform is filtered by cross-correlation with the pilot sweep followed by application of a time window to remove the harmonics of the pilot sweep.

5. A method as claimed in claim 1, wherein each measured force waveform is filtered by cross-correlation with the same pilot sweep followed by application of a time window to remove the harmonics of the pilot sweep.

6. A method as claimed in claim 4, wherein the time window is applied to include zero time after cross-correlation.

7. A method as claimed in claim 1, wherein each measured seismic signal is filtered by cross-correlation with the pilot sweep followed by application of a time window before the application of the inversion operator.

8. A method as claimed in claim 1, wherein the pilot sweep comprises a waveform having a substantially constant amplitude envelope with tapered ends, within which the frequency increases with time.

9. A method as claimed in claim 1, wherein the number of sweeps is the same as the number of vibrators.

10. A method as claimed in claim 1, wherein the number of sweeps is greater than the number of vibrators, and wherein the noise on each measured seismic signal is estimated and used in the determination of the inversion operator.

11. A method of performing a seismic survey, comprising:

performing a plurality of sweeps, wherein each sweep comprises generating seismic signals in the earth using a plurality of vibrators by applying a pilot sweep waveform to each vibrator, each pilot sweep being a waveform of changing frequency;

measuring the force applied to the earth by each vibrator to determine a measured force waveform;

measuring the seismic signals at one or more locations remote from the vibrators; and

processing seismic data comprising the measured seismic signals and the measured force waveform using the the steps of

filtering the measured force waveform to remove harmonics of the pilot sweep from the measured force waveform and thus determining a filtered force waveform;

generating an inversion operator from the filtered force waveform for each vibrator; and

applying said inversion operator to the measured seismic signals to determine the contribution of each vibrator to the seismic signals.