Loading patent…
AssigneeInstitut Francais du Petrole
InventorMarc Becquey
Estimating the term…
Seismic prospecting method and device using simultaneous emission, by several 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 reflected by the subsoil discontinuities in response to the periodic signals emitted are picked up by receivers coupled with the formation and recorded in an acquisition and recording system. The seismic signals emitted are formed either from elementary sequences whose length is at least equal to the product of the number of seismic souces vibrating simultaneously by the listening time, or from this 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 either by signals constructed from said elementary sequence extended, before and after, with parts whose length is at least equal to the listening time, obtained by circular permutation, or of said elementary sequence.
1) A method intended for prospecting or monitoring of an underground formation by elastic waves, comprising simultaneous emission, in the ground, of seismic waves by several seismic sources (V1 to Vm) controlled each by a signal consisting either of an elementary sequence formed by coding of a signal by pseudo-random sequences, the length of each elementary sequence being at least equal to the product of the number of seismic sources vibrating simultaneously by the listening time, or respectively of this elementary sequence extended, before and after, with parts whose length is at least equal to the listening time, reception and recording of the signals reflected by the subsoil discontinuities in response to the signals emitted, and processing of the signals recorded, the respective contribution of each one of the various seismic sources being separated by correlating the signals received and recorded either by signals constructed from said elementary sequence, extended, before and after, with parts whose length is at least equal to the listening time, obtained by circular permutation, or respectively of said elementary sequence, characterized in that the signals applied to the various vibrators are formed from a periodic signal whose amplitude and derivatives with respect to the amplitude time are equated to zero at the beginning and at the end of each period, and such that its integral over a period is zero.
7) A device intended for prospecting or monitoring of an underground formation by elastic waves, comprising at least a group of m vibrators (V1-Vm), a control unit (1) for controlling the various vibrators by phase modulated periodic signals, seismic receivers (R1-Rk) coupled with the formation, a system (2) intended for acquisition and recording of the seismic signals reflected by the subsoil discontinuities in response to the periodic signals emitted and a system (3) for processing the seismic signals recorded, by correlation with part of the periodic signals emitted, characterized in that control unit (1) includes a signal generator (4) and a modulation set (MA) for forming m elementary sequences phase modulated by a pseudo-random sequence and connection means (L) for applying simultaneously to the various vibrators (V1-Vm) of each group the signals produced by the modulation set.
Dependencies are inferred from the claim text.