Method for seismic exploration
View Patent ↗The invention relates to a method for seismic exploration, comprising the steps of controlling a plurality of sources so that they emit a plurality of seismic waves in a subsurface zone to be explored, each source successively occupying a plurality of emitter positions, producing for each emission a signal representative of the emission, and recording the position of the source and the instant at which the emission starts, continuously recording by means of seismic sensors the composite signals reflected by the medium in response to said emissions, and carrying out shot point migration, on the one hand, from a reflected wave field constituted of said composite signals and respective sensor positions, and on the other hand, from an incident wave field constituted of signals representative of the emissions, source positions and start emission instants, so as to obtain a seismic image.
1. A method for seismic exploration, comprising the steps of:
controlling a plurality of sources so that they emit a plurality of seismic waves in a subsurface zone to be explored, each source successively occupying a plurality of emitter positions;
producing for each emission an emission signal, and recording the position of the source and the instant of the start of the emission;
recording, by seismic sensors, composite signals reflected by the subsurface zone in response to said emissions; and
carrying out a shot point migration from a reflected wave field reconstructed from the composite signals and the respective positions of the sensors, and an incident wave field reconstructed from the emission signals, the source positions and the instants of start of emission, to obtain a seismic image, wherein the shot point migration uses a product of a Fourier transform of the reflected wave field and a conjugate of a Fourier transform of the incident wave field to determine a reflectivity r associated with the subsurface zone.
2. The method according to claim 1 , further comprising a step of local deconvolution concerning at least a part of the points of the subsurface zone, the step of deconvolution comprising determining a deconvolved reflectivity r′ in the part of the points, the deconvolved reflectivity being obtained by calculating the local autocorrelation matrices from:
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and then by solving the linear systems from:
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where I(x,y,z,f) is a Fourier transform of the incident wave i, I(x,y,z,f) is a conjugate of I(x,y,z,f), and f is a frequency.
3. The method according to claim 1 , adapted to land seismics, wherein the sources are vibrators and the sensors are geophones.
4. The method according to claim 1 , adapted to marine seismics, wherein the sources are impulse sources and the sensors are hydrophones.
5. The method according to claim 4 , wherein the sources comprise at least one air gun operated at instants determined by a random sequence.
6. A method for processing data for forming a seismic image of a subsurface zone, comprising the step of:
carrying out a shot point migration from:
an incident wave field reconstructed from emission signals, source positions and emission start instants associated with each emission, and
a reflected wave field reconstructed from composite signals reflected by the subsurface zone in response to the emissions recorded by seismic sensors, and sensor positions, wherein the shot point migration uses a product of a Fourier transform of the reflected wave field and a conjugate of a Fourier transform of the incident wave field to determine a reflectivity r associated with the subsurface zone.
7. The method according to claim 6 , comprising a step of local deconvolution concerning at least part of the points of the subsurface zone comprising determining a deconvolved reflectivity r′ in the part of the points, the deconvolved reflectivity being obtained by calculating the local autocorrelation matrices from:
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where I(x,y,z,f) is a Fourier transform of an incident wave i, I(x,y,z,f) is a conjugate of I(x,y,z,f), and f is a frequency.
8. A method for the acquisition of seismic data, comprising the steps of:
controlling a plurality of sources so that they emit a plurality of seismic waves in a subsurface zone to be explored, each source successively occupying a plurality of emitter positions;
producing, for each emission, an emission signal, and recording the position of the source and the instant of the start of emission;
recording, by seismic sensors, composite signals reflected by the subsurface zone in response to said emissions and the sensor positions;
the emission being exempt from conditions intended to separate the contributions from different sources in the composite signals; and
determining a reflectivity r associated with the subsurface zone, wherein the reflectivity is given by a product of a Fourier transform of a reflected wave field and a conjugate of a Fourier transform of an incident wave field, wherein the incident wave field is reconstructed emission and emission start instants associated with each emission, and the reflected wave field is reconstructed from the composite signals reflected by the subsurface zone in response to the emissions, and the sensors positions.
9. The method according to claim 8 , wherein the distances between sources comprise between 10 meters and about 1 kilometer.
10. The method for acquisition according to claim 8 , wherein the sources are vibrators and the sensors are geophones.
11. The method for acquisition according to claim 8 , wherein the sources are impulse sources and the sensors are hydrophones.
12. The method according to claim 11 , wherein the sources comprise of at least one air gun operated at instants determined by a random sequence.
13. The method according to claim 11 , wherein the sources comprise a plurality of air guns operated independently from each other.
14. The method according to claim 1 , wherein the incident wave field is composed of a plurality of superposed signals corresponding to the plurality of sources.
15. The method of claim 1 , wherein the plurality of sources is configured to emit non-orthogonal signals that interfere among them.
16. The method of claim 1 , wherein each composite signal recorded by the seismic sensors includes a sum of signals from the plurality of sources.
17. The method according to claim 6 , wherein the incident wave field is composed of a plurality of superposed signals corresponding to the plurality of sources.
18. The method of claim 6 , wherein the plurality of sources is configured to emit non-orthogonal signals that interfere among them.
19. The method of claim 6 , wherein each composite signal recorded by the seismic sensors includes a sum of signals from the plurality of sources.
20. The method according to claim 8 , wherein the incident wave field is composed of a plurality of superposed signals corresponding to the plurality of sources.