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AssigneeInstitut Francais du Petrole
InventorsJean-Claude Dubois, Marc Becquey
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Vibrator comprising a single vibration generator coupled with the medium by a coupling element and means for controlling the generator, suited to apply thereto, on each emission, a single pilot signal obtained by combination of at least two signals of different frequencies (f1, f2), fixed or preferably variable within at least partly separate frequency bands, and non-linear elastic transmission means suited to generate in the medium vibrations at a frequency depending on the frequency difference of the two vibrational signals. The exploration method comprises using the vibrator in order to emit very low-frequency vibrations in the medium, reception by pickups (R) of the waves reflected by the medium in response to the vibrations emitted and recording thereof, and selection by correlation of the vibrational signals with a synthetic signal whose frequency is connected with the frequency difference of the signals forming the pilot signal. Applications: seismic prospecting for example.
A vibrator intended to generate vibrations in the ground (M), comprising a single vibration generator (2), a control module (A) for the single generator (2) suited to apply thereto, on each emission, a pilot signal obtained by combination of at least two signals of different frequencies (f1, f2), characterized in that it comprises coupling means allowing the vibrator to lean tightly against the ground, and non-linear elastic transmission means suited to generate in the medium vibrations at a frequency depending on the frequency difference (f1, f2) of the two vibrational signals, comprising at least a surface layer of the ground having an acoustic impedance discontinuity in relation to the underlying layers.
A vibrator as claimed in any one of the previous claims, characterized in that control module (A) intended to generate the pilot signal comprises a fixed-frequency oscillator and an oscillator whose frequency can vary within a determined frequency range.
A method of exploring a material medium by means of very low-frequency vibrations with emission of vibrations in the medium, reception of the vibrations coming from the medium in response to the vibrations emitted and recording of the waves received, characterized in that, on each emission, at least one composite pilot signal obtained by combination of at least two vibrational signals of different frequencies is applied to at least one vibrator (1), and the signals generated by each vibrator are applied to the medium by non-linear elastic transmission means (5, 6) so as to generate in the medium vibrations whose emission spectrum includes at least one frequency equal to the frequency difference of the two vibrational signals.
Dependencies are inferred from the claim text.