Source waveforms for electroseismic exploration
AssigneeExxonMobil Upstream Research Company
InventorsScott C. Hornbostel, Arthur H. Thompson
Life of this patent
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Abstract
A method for seismic exploration using conversions between electromagnetic and seismic energy, with particular attention to the electromagnetic source waveform used. According to the invention, source waveforms are correlated with reference waveforms selected to minimize correlation side lobes. Line power at 60 Hz may be used to provide a waveform element which may be sequenced by a binary code to generate an extended source waveform segment with minimal correlation side lobes. Preferred binary codes include Golay complementary pairs and maximal length shift-register sequences.
Claims20
A method for electroseismic prospecting of a subterranean formation, said method comprising the steps of:
- selecting a source waveform and corresponding reference waveform, said two waveforms being selected to reduce amplitudes of side lobes produced by correlating said source waveform with said reference waveform;
- generating said source waveform as an electrical signal and transmitting said electrical signal into said subterranean formation;
- detecting and recording seismic signals resulting from conversion of said electrical signal to seismic energy in said subterranean formation;
- and
- correlating said recorded seismic signals with said reference waveform.
A method for electroseismic prospecting of a subterranean formation, said method comprising the steps of:
- constructing a first source waveform and a second source waveform from a single element, said element consisting of a single full cycle of a preselected periodic waveform, said periodic waveform having a frequency predetermined to give desired depth penetration of said subterranean formation, said elements being pieced together with polarities specified sequentially by one member of a Golay complementary pair of binary sequences in the case of said first source waveform, and by the second member of said Golay complementary pair in the case of said second source waveform;
- generating each of said two source waveforms as an electrical signal, and transmitting each said electrical signal, in turn, into said subterranean formation;
- detecting and recording seismic signals resulting from conversion of said electrical signals to seismic energy in said subterranean formation;
- correlating said recorded seismic signals from each of said source waveforms with said respective source waveform itself;
- and
- summing said pair of correlations of said recorded seismic signals and their corresponding source waveform.
An electrical signal for use in electroseismic prospecting of a subterranean formation, said signal having a waveform constructed from a single element, said element consisting of a single full cycle of a preselected periodic waveform, said elements being pieced together with polarities sequentially specified by a preselected binary code, said periodic waveform having a frequency predetermined to give desired depth penetration of said subterranean formation, said binary code being selected to generate side lobe amplitudes below a predetermined level when the signal waveform is correlated with itself.
An electrical signal for use in electroseismic prospecting of a subterranean formation, said signal having a waveform constructed from a single element, said element consisting of a single full cycle of a preselected periodic waveform, said periodic waveform having a frequency predetermined to give desired depth penetration of said subterranean formation, said elements being pieced together with polarities sequentially specified by a maximal length shift-register sequence, said resulting signal waveform being modified such that resulting negative polarity elements are zeroed.
A pair of complementary electrical signals for use in conjunction with each other in electroseismic prospecting of a subterranean formation, said signals having waveforms constructed from a single element, said element consisting of a single full cycle of a preselected periodic waveform, said periodic waveform having a frequency predetermined to give desired depth penetration of said subterranean formation, said elements being pieced together with polarities sequentially specified by one member of a Golay complementary pair of binary sequences in the case of one of said two electrical signals, and by the second member of said Golay complementary pair in the case of the other electrical signal.
Dependencies are inferred from the claim text.