Institut Francais Du Pe'trole

Marc Becquey

Jean-Claude Dubois

A seismic prospecting method and device is disclosed using simultaneous emission, by vibrators, of seismic signals obtained by phase modulating a periodic signal whose amplitudes and derivatives with respect to the amplitude time are equated to zero at the beginning and at the end of each period, by pseudo-random sequences. The seismic signals are formed either from elementary sequences whose length is at least equal to the product of the number of seismic sources vibrating simultaneously by a listening time, or from the elementary sequence extended, before and after, with parts whose length is at least equal to the listening time, the reception and recording of the signals reflected by the subsoil discontinuities in response to the signals emitted, and the processing of the recorded signals. The respective contributions of the various seismic sources are isolated by correlating the signals received and recorded.

Seismic prospecting method and device using simultaneous emission of seismic signals based on pseudo-random sequences

Seismic prospecting method and device using simultaneous emission of seismic signals obtained by coding a signal by pseudo-random sequences

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 (f , f ), 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.

Vibrator and method of exploring a material medium by means of very low-frequency elastic vibrations

The present invention relates to a filtering method for discriminating elliptical waves among other waves propagating in a material medium (such as a geologic formation for example) by a combined processing of the components measured along several axes of the waves received by a multi-axis receiver. It comprises detection by at least one receiver (R) (consisting for example of one or several directional detectors such as geophones or accelerometers coupled with said formation) of the wave components in at least two orthogonal directions. A determination (by a processing assembly (1)) of the wavelet transforms of the signals is produced by this receiver (R) in response to the waves received and selection of the amplitudes of the signals resulting from this wavelet transformation is performed according to a criterion based on the ratio of the respective amplitudes thereof. The method can be used for the filtering of surface or tube waves within the scope of a seismic exploration.

Method and device for filtering elliptical waves propagating in a medium

An offshore reflection seismic prospection method is provided including a vibratory signal coded in accordance with a pseudo-random code. Correlation of the signals received by the seismic sensors by means of the cycle of the coded signal transmitted allows seismic plots to be obtained similar to what a pulsed source would provide firing at time intervals equal to the duration of the cycle of the coded signal. Correlation with time shifted cycles reduces the distance between plots recorded on the same sensor. The transmissions coming from two or more vibrators, transmitting the same coded signal with shifted cycles, may be separated by correlation with one of the cycles used.

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Rueil Malmaison, France

Marc Becquey