Method of using cascaded sweeps for source coding and harmonic cancellation
First Claim
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1. A method for recording and processing vibratory source seismic data, the method comprising:
- (a) generating a cascaded sweep sequence comprising N sweep segments that are either concatenated or overlapping sequentially, where N is equal to or greater than 2, said N sweep segments being substantially identical, except that the initial phase angles of said N sweep segments are progressively rotated by a constant phase increment of about 2 m π
/N radians where m is an integer and |m|>
1;
(b) using said cascaded sweep sequence to drive at least one vibratory source thereby propagating a seismic wave into the earth at a selected location;
(c) recording a groundforce signal associated with said seismic wave;
(d) recording at least one reflection signal from a location within the earth responsive to said seismic wave; and
(e) using said recorded groundforce signal for processing the signal recorded to produce a processed signal.
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Abstract
A method of seismic surveying using one or more vibrational seismic energy sources activated by sweep signals. The highest order harmonic that has sufficient strength to cause significant harmonic distortion of a sweep segment is determined. A number of sweep segments in excess of the number of sources is selected. Initial phase angles are selected for each sweep segment of each seismic energy source so that substantially all harmonics up to and including the highest order harmonic are suppressed. Using cascaded sweeps, seismic data are acquired and processed to substantially attenuate harmonics upto the selected order.
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Citations
20 Claims
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1. A method for recording and processing vibratory source seismic data, the method comprising:
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(a) generating a cascaded sweep sequence comprising N sweep segments that are either concatenated or overlapping sequentially, where N is equal to or greater than 2, said N sweep segments being substantially identical, except that the initial phase angles of said N sweep segments are progressively rotated by a constant phase increment of about 2 m π
/N radians where m is an integer and |m|>
1;
(b) using said cascaded sweep sequence to drive at least one vibratory source thereby propagating a seismic wave into the earth at a selected location;
(c) recording a groundforce signal associated with said seismic wave;
(d) recording at least one reflection signal from a location within the earth responsive to said seismic wave; and
(e) using said recorded groundforce signal for processing the signal recorded to produce a processed signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for recording and processing vibratory source seismic data, the method comprising:
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(a) simultaneously transmitting, with n vibratory sources where n≧
1, associated ground force signals into the earth, each said ground force signal including a fundamental signal and harmonics thereof, said fundamental signal having an initial phase;
(b) recording said n ground force signals;
(c) recording at least one reflection signal from a location within the earth responsive to n ground force signals to give a first recorded signal;
(d) repeating steps (a)-(c) m−
1 times wherein said initial phases are shifted by 2π
/m radians to give a total of m recorded signals and n×
m ground force signals; and
(e) using the n×
m ground force signals for processing the m recorded signals to give processed signals associated with said n vibratory sources. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A method for recording and processing vibratory source seismic data, the method comprising:
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(a) selecting a number of seismic energy sources to be used for surveying;
(b) selecting a number of a highest order harmonic that has sufficient strength to cause significant harmonic distortion of a sweep segment that is part of a sweep sequence;
(c) defining a reference signal associated with each of said sources, each reference signal comprising a number N of sweep segments, N being greater than the number of seismic sources, said sweep segments being either concatenated or overlapping;
(d) selecting initial phase angles for each sweep segment of each reference signal so that substantially all harmonics up to and including said highest order harmonic are suppressed and driving each vibratory source with its sweep sequence and driving each of said sources with its associated reference signal, thereby generating seismic waves propagating into the earth;
(e) recording ground force signals associated with each reference signal;
(f) recording at least one reflection signal from a location within the earth responsive to said seismic waves; and
(g) using said ground force signals for processing said at least one recorded reflection signal. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification