Method for seismic monitoring of an underground zone by simultaneous use of sererval vibroseismic sources
First Claim
1. A method of seismic monitoring an underground formation comprising:
- continuously emitting seismic waves in the formation by coupling with the formation at least two vibrators which emit seismic waves simultaneously and are controlled by orthogonal pilot signals, each pilot signal having a fundamental component and harmonics thereof, frequencies of the fundamental component and of the harmonics thereof being different so as to form a composite vibrational signal;
receiving signals emanating from the formation in response to the emitted seismic waves and recording the received signals; and
processing the recorded signals including discriminating respective contributions of the vibrators to the composite vibrational signal and reconstructing seismograms equivalent to seismograms that would be obtained by actuating the vibrators separately.
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Accused Products
Abstract
Method and system intended for seismic monitoring of an underground zone (1), comprising simultaneously using several seismic vibrators. The system comprises for example several local units (LU) comprising each a vibrator (5), a seismic pickup antenna (2), a local acquisition and processing unit (6), and a central control and synchronization unit (8) for simultaneously controlling the various vibrators by means of orthogonal signals, local units (6) being suited, by means of particular; processing, to isolate and to reconstitute the seismograms corresponding to the contributions of the various vibrators. Applications: monitoring of a hydrocarbon reservoir during production or of a reservoir used for gas storage for example.
85 Citations
13 Claims
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1. A method of seismic monitoring an underground formation comprising:
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continuously emitting seismic waves in the formation by coupling with the formation at least two vibrators which emit seismic waves simultaneously and are controlled by orthogonal pilot signals, each pilot signal having a fundamental component and harmonics thereof, frequencies of the fundamental component and of the harmonics thereof being different so as to form a composite vibrational signal;
receiving signals emanating from the formation in response to the emitted seismic waves and recording the received signals; and
processing the recorded signals including discriminating respective contributions of the vibrators to the composite vibrational signal and reconstructing seismograms equivalent to seismograms that would be obtained by actuating the vibrators separately. - View Dependent Claims (2, 3, 4, 5, 6, 7)
the orthogonal signals are sinusoids.
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3. A method as claimed in claim 2, wherein:
discrimination of the respective contributions of the vibrators includes determining an amplitude and a phase of the composite vibrational signal at fundamental frequencies of the pilot signals controlling the at least two vibrators.
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4. A method as claimed in claim 2, wherein:
discrimination of the respective contributions of the vibrators includes weighting the recorded signals by a bell weighting factor and determining an amplitude and a phase of the composite signal.
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5. A method as claimed in claim 2, wherein:
discrimination of the respective contributions of the vibrators includes weighting the recorded signals by a bell weighting factor and determining an amplitude and a phase of the composite signal and the discrimination of the respective contributions of the vibrators includes selecting, by Fourier transform, lines of a spectrum respectively associated with the weighted recorded signals.
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6. A method as claimed in claim 4, herein:
reconstruction of the seismograms corresponding to the at least two vibrators includes applying, after separation thereof, an inverse Fourier transform to lines of the spectrum respectively associated with the weighted signals.
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7. A method as claimed in claim 2, comprising:
shifting respective frequencies of the orthogonal pilot signals by frequency intervals, at predetermined time intervals, so as to sweep an emission frequency band.
- 8. A system for seismic monitoring of an underground formation, comprising at least two vibrators to be coupled with the formation, an assembly for generating sinusoidal orthogonal pilot signals, each pilot signal comprising a fundamental component and harmonics thereof, respective frequencies of the fundamental component and the respective harmonics thereof being different and a connecting means for applying the orthogonal pilot signals respectively to the at least two vibrators to generate in the formation a composite vibrational signal, a seismic reception device for reception of seismic signals emanating from the formation in response to the emitted seismic waves, a recording set for recording the received signals, and a processing means including f at least one processor for discriminating respective contributions of the at least two vibrators to the composite vibrational signal and reconstructing seismograms equivalent to seismograms that would be obtained by actuating the vibrators separately.
Specification