Patent EA-003029-B1 (EA)
Title: Method for seismic monitoring of an underground zone by simultaneous use of several vibroseismic sources
Inventor: MEUNIER JULIEN
IPC: G01V1/00
Filed: 2001-02-09
Abstract: 1. A method for monitoring an underground zone (1) comprising emitting seismic waves to a formation, reception of the reflected waves by the formation in response to the emission of the seismic waves, registration of the received signals using at least one seismic sensor (4) and a formation a seismogram by processing the registered signals, characterized in that signals are emitted by connecting to a formation at least two vibrators (5) emitting signals simultaneously controlled, being orthogonal respective to each other to constitute sinusoids with frequencies differ both as fundamental components and as respective harmonics to form a composite signal from vibrators, and processing the registered signal which comprises discrimination mutual influence of vibrators on a composite signal and reconstructing seismogram equivalent to those which could be obtained activating vibrators separately 2. The process of claim 1, characterized in that orthogonal signals are emitted formed on the basis of disturbances, Legendre`s polynoms or random series. 3. The process of claim 1, characterized in that the mutual influences of vibrators are discriminated by determining an amplitude and a phase of the composite signal from vibrators with fundamental frequencies of control signals. 4. The process of any claims 1 to 3, characterized in that for discrimination of mutual influences of vibrators (5) the signals are balances registered through weighting cone-shaped coefficient and discriminate amplitude and phase of a composite signal. 5. The process of claim 4, characterized in that for discrimination of mutual influences of vibrators (5) a complex specter for respective different balanced signals is separated by transforming the Fourier bands (15-18). 6. The process of any claims 1 to 5, characterized in that seismograms specially for different vibrators are formed applying the Fourier inversion to bands (19,20) after their separation associated respectively to different balanced signals. 7. The process of any claims 1 to 6, characterized in that using a frequency step frequencies of control signals are shifted in determined time intervals applied respectively to vibrators such that to scan a certain band with an emission frequency [fb-ff]. 8. A system for monitoring an underground zone (1) comprising means for emitting seismic waves to a formation, means for receiving signals of the reflected waves by the formation in response to the emission of the seismic waves, means for registering of the received signals using by the reception means and means for processing the registered signals meat least one seismic sensor (4) and a formation a seismogram by processing the registered signals to form seismograms, characterized in that the means for emitting seismic waves comprise at least two vibrators (5) and means (8) for generating signals orthogonal relative to each other which are frequency sinusoids differ from each other both as fundamental components and as respective harmonics and mutual use of vibrators (5) for generating a composite signal to the earth formation, the procession means comprise at least a processing unit (6) adapted for discrimination in the domain frequency mutual effects of vibrators with composite vibrator signals and for forming seismograms equivalent to those which can be obtained activating the vibrators separately. 9. The system of claim 8, characterized in that comprises a plurality of local units (LU) disposed at a distance from each other and connected to an earth formation, each unit comprises at least one seismic vibrator (5), and one central control and synchronising unit (8) connected to different local units, a generator of signals adapted to the vibrators (5) for controlling the orthogonal signals. 10. The system of claim 9, characterized in that the central control and synchronising unit (8) is connected to different local units by different liaison means material or non material origin. 11. The system of claim 9 or 10, characterized in that comprises a plurality of local units (LU) disposed at a distance from each other and connected to an earth formation, each unit comprises at least one seismic capturing sensor (4), one seismic vibrator (5), one acquisition and processing local unit (6) and a central control and synchronising unit (8) connected to different local units, a generator of signals adapted to form different orthogonal controlling signals, and means for receiving the signals using antennae (2) and forming seismograms corresponding to the contribution of different vibrators.