Time delay source coding

• US 4,953,657 A
• Filed: 02/14/1989
• Issued: 09/04/1990
• Est. Priority Date: 11/30/1987
• Status: Expired due to Term

• Current Assignee: WesternGeco LLC
• Original Assignee: Halliburton Geophysical Services, Inc. (Baker Hughes Company)
• Inventors: Edington, Bruce L.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Lobo, Ian J.
• Application Number:
  US07/312,360
• Time in Patent Office: 567 Days
• Field of Search: 181/111, 367/50, 367/55, 367/47
• US Class Current: 181/111
• 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 1/37 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 2210/127 Cooperating multiple sources

Abstract

In seismic exploration, a survey may be conducted using multiple seismic energy sources activated substantially simultaneously. A series of shots is made at each shot point, with a determinable time delay between the activation of each source for each shot. There must be at least two different determinable time delays in each series of shots. The seismic signals are recorded. A method of processing the signals to separate signals from each source is provided. For each signal receiver, the amplitudes of the signals from each shot in the series is summed. The signals are then time shifted, so that the signals from the second source to be activated are received at the same time, and the amplitudes for the series are summed. This step is repeated for each subsequently activated source. Time domain operators are derived, the operators and the summations Fourier transformed to the frequency domain, in which the signals received from each source are readily calculated. The separated signals may then be inverse Fourier transformed to the time domain.

Claims

1. A method of obtaining seismic data for a geophysical survey, said method comprising the steps of:

activating a first seismic energy source having a selected frequency component;

receiving seismic signals from said first seismic energy source at at least one point within said geophysical survey;

activating a second seismic energy source after a first selected time delay from activation of said first seismic energy source and while said seismic signals from said first seismic energy source are being received, said first selected time delay being a nonintegral multiple of the period of said selected frequency component;

receiving seismic signals from said second seismic energy source at said at least one point within said geophysical survey;

activating said first seismic energy source a second time;

receiving seismic signals from said second activation of said first seismic energy source at said at least one point within said geophysical survey;

activating said second seismic energy source after a second selected time delay from said second activation of said first seismic energy source and while said seismic signals from said second activation of said first seismic energy source are being received;

recording, as a function of time, the amplitudes of the seismic signals received at said at least one point within said geophysical survey for each activation of said first and second seismic energy source; and

analyzing said recorded seismic signal amplitudes utilizing said selected time delays in order to separate signals originating from each of said seismic energy sources.

2. A method of obtaining seismic data for a geophysical survey according to claim 1 wherein said first and second seismic energy sources are surface energy sources.

3. A method of obtaining seismic data for geophysical survey according to claim 1 wherein said second selected time delay comprises a non-integral multiple of the period of said selected frequency component.

4. A method of obtaining seismic data for geophysical survey according to claim 1 wherein said first selected time delay comprises not less than one-quarter and not more that three-quarters of the period of said selected frequency component.

5. A method of obtaining seismic data for geophysical survey according to claim 1 wherein the step of recording the amplitudes of the seismic signals received at said at least one point within said geophysical survey comprises digitally recording said amplitudes.

6. A method of obtaining seismic data for a geophysical survey, said method comprising the steps of:

activating a first seismic energy source having a selected frequency component;

receiving seismic signals from said first seismic energy source at at least one point within said geophysical survey;

activating a second seismic energy source after a first selected time delay from activation of said first seismic energy source and while said seismic signals from said first seismic energy source are being received, said first selected time delay being a non-integral multiple of the period of said selected frequency component;

receiving seismic signals from said second seismic energy source at said at least one point within said geophysical survey;

activating said first seismic energy source a second time;

receiving seismic signals from said second activation of said first seismic energy source at said at least one point within said geophysical survey;

activating said second seismic energy source after a second selected time delay from said second activation of said first seismic energy source and while said seismic signals from said second activation of said first seismic energy source are being received;

recording, as a function of time, the amplitudes of the seismic signals received at said at least one point within said geophysical survey for each activation of said first and second seismic energy source;

summing the amplitudes of the received seismic signals from each activation as a function of time;

utilizing said selected time delays to time shift the received seismic signals from each activation so that the signals received from said second source are received at the same times for each activation;

summing the amplitudes of said time shifted seismic signals as a function of time;

utilizing said selected time delays to derive an appropriate time domain operator for each summation;

deriving the Fourier transform to the frequency domain of each time domain operator;

deriving the Fourier transform to the frequency domain of each summation;

calculating the signals received from each seismic energy source in the frequency domain for each frequency; and

deriving the inverse Fourier transform to the time domain of the signals received from each seismic energy source.

7. A method of obtaining seismic data for a geophysical survey according to claim 6 wherein said first and second seismic energy sources are surface energy sources.

8. A method of obtaining seismic data for geophysical survey according to claim 6 wherein said second selected time delay comprises a non-integral multiple of the period of said selected frequency component.

9. A method of obtaining seismic data for geophysical survey according to claim 6 wherein said first selected time delay comprises not less than one-quarter and not more that three-quarters of the period of said selected frequency component.

10. A method of obtaining seismic data for geophysical survey according to claim 6 wherein the step of recording the amplitudes of the seismic signals received at said at least one point within said geophysical survey comprises digitally recording said amplitudes.