3D prestack seismic data migration method
First Claim
1. A method of performing prestack migration of seismic events for imaging a part of an underground zone from a series of a number Ns of seismic reflection cycles, comprising successive emission of elementary wavefields, each elementary wavefield defined by association of a seismic signal W(t) and points of emission defined in a series of points of emission Si with 1≦
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Ns, seismic receivers located at points of reception Rji of receiving seismic signals reflected by the underground zone in response to each of the wavefields, with signals received by each seismic receiver being recorded as time-dependent seismic traces dji(t), wherein for a given velocity model, the method comprises the following steps;
a) applying an azimuth moveout correction to data representing the recorded seismic signal sensed by the different receivers located at the points of reception for having all directions between the points of emission and the points of reception collinear to a common direction;
b) defining a slowness vector p having components p1 and p2 assuming a series of previously defined values;
c) defining, for a given slowness vector p and for a given point of emission Si, a time lag function t0(p, i);
d) applying the time lag function t0(p, i) to each elementary wavefield associated with point of emission Si and forming a surface composite wavefield by spatiotemporal superposition of elementary wavefields to which such a time lag is applied;
e) applying the time lag function t0(p, i) to seismic traces dji(t) marked by a pair (i,j) and forming a surface composite trace field by spatiotemporal superposition of the seismic traces to which the time lag is applied;
f) performing migration of the surface composite trace field using the surface composite wavefield, by modelling propagation of the surface composite wavefield and retropropagation of the surface composite trace field, and combining the modelled propagation of the surface composite wavefield and the retropropagation of the surface composite trace field at any point of the zone to be imaged;
g) repeating steps c) to e) for all values assumed by the components p1 and p2 of the vector p; and
h) for any set value of the second component p2 of the vector p, stacking the results of combinations of the surface composite wavefield and the retropropagation of the surface composite tracer field to obtain a migrated image associated with the set value of p2, to thereby perform prestack migration.
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Abstract
A prestack migration method allowing imaging of an underground zone, for a given velocity model of arbitrary complexity. The method allows obtaining elementary migrated images associated with the values assumed by a parameter and the sum of the images obtained for the different values of the parameter (post-migration stacking), in the depth domain as well as in the time domain. This migration is independent of the volume of the results calculated and of the number of seismic traces recorded. Volume images are obtained by taking account of all the seismic traces. Azimuth movout correction is applied to the received data to compensate for drift.
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Citations
39 Claims
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1. A method of performing prestack migration of seismic events for imaging a part of an underground zone from a series of a number Ns of seismic reflection cycles, comprising successive emission of elementary wavefields, each elementary wavefield defined by association of a seismic signal W(t) and points of emission defined in a series of points of emission Si with 1≦
- i≦
Ns, seismic receivers located at points of reception Rji of receiving seismic signals reflected by the underground zone in response to each of the wavefields, with signals received by each seismic receiver being recorded as time-dependent seismic traces dji(t), wherein for a given velocity model, the method comprises the following steps;a) applying an azimuth moveout correction to data representing the recorded seismic signal sensed by the different receivers located at the points of reception for having all directions between the points of emission and the points of reception collinear to a common direction;
b) defining a slowness vector p having components p1 and p2 assuming a series of previously defined values;
c) defining, for a given slowness vector p and for a given point of emission Si, a time lag function t0(p, i);
d) applying the time lag function t0(p, i) to each elementary wavefield associated with point of emission Si and forming a surface composite wavefield by spatiotemporal superposition of elementary wavefields to which such a time lag is applied;
e) applying the time lag function t0(p, i) to seismic traces dji(t) marked by a pair (i,j) and forming a surface composite trace field by spatiotemporal superposition of the seismic traces to which the time lag is applied;
f) performing migration of the surface composite trace field using the surface composite wavefield, by modelling propagation of the surface composite wavefield and retropropagation of the surface composite trace field, and combining the modelled propagation of the surface composite wavefield and the retropropagation of the surface composite trace field at any point of the zone to be imaged;
g) repeating steps c) to e) for all values assumed by the components p1 and p2 of the vector p; and
h) for any set value of the second component p2 of the vector p, stacking the results of combinations of the surface composite wavefield and the retropropagation of the surface composite tracer field to obtain a migrated image associated with the set value of p2, to thereby perform prestack migration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
forming a final image representative of post-migration stacking of the surface composite trace fields obtained for all values p2 of vector p.
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3. A method as claimed in claim 2, wherein:
a migrated image of a part of the zone to be imaged is formed by using a wave conversion phenomenon, by definition of at least a part of a velocity field in P waves and S waves.
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4. A method in accordance with claim 2, wherein:
the migration of a surface composite trace field is a time migration.
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5. A method in accordance with claim 2, wherein:
the migration of a surface composite trace field is a depth migration.
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6. A method as claimed in claim 3, comprising:
using preprocessing to separate seismic events.
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7. A method in accordance with claim 3, wherein:
the migration of a surface composite trace field is a time migration.
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8. A method in accordance with claim 3, wherein:
the migration of a surface composite trace field is a depth migration.
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9. A method in accordance with claim 6, wherein:
the migration of a surface composite trace field is a time migration.
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10. A method in accordance with claim 6, wherein:
the migration of a surface composite trace field is a depth migration.
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11. A method as claimed in claim 1 wherein:
- steps a) to g) are used to directly perform post-migration stacking.
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12. A method as claimed in claim 11, wherein:
a migrated image of a part of the zone to be imaged is formed by using a wave conversion phenomenon, by definition of at least a part of a velocity field in P waves and S waves.
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13. A method in accordance with claim 11, wherein:
the migration of a surface composite trace field is a time migration.
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14. A method in accordance with claim 11, wherein:
the migration of a surface composite trace field is a depth migration.
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15. A method as claimed in claim 12, comprising:
using preprocessing to separate seismic events.
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16. A method in accordance with claim 12, wherein:
the migration of a surface composite trace field is a time migration.
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17. A method in accordance with claim 12, wherein:
the migration of a surface composite trace field is a depth migration.
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18. A method in accordance with claim 15, wherein:
the migration of a surface composite trace field is a time migration.
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19. A method in accordance with claim 15, wherein:
the migration of a surface composite trace field is a depth migration.
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20. A method as claimed in claim 1, further comprising:
updating of velocities of the seismic signals W(t) by analysis of deformations obtained when a value p2 of vector p is varied.
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21. A method as claimed in claim 20, wherein:
a migrated image of a part of the zone to be imaged is formed by using a wave conversion phenomenon, by definition of at least a part of a velocity field in P waves and S waves.
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22. A method in accordance with claim 20, wherein:
the migration of a surface composite trace field is a time migration.
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23. A method in accordance with claim 20, wherein:
the migration of a surface composite trace field is a depth migration.
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24. A method as claimed in claim 21, comprising:
using preprocessing to separate seismic events.
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25. A method in accordance with claim 21, wherein:
the migration of a surface composite trace field is a time migration.
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26. A method in accordance with claim 21, wherein:
the migration of a surface composite trace field is a depth migration.
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27. A method in accordance with claim 24, wherein:
the migration of a surface composite trace field is a time migration.
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28. A method in accordance with claim 24, wherein:
the migration of a surface composite trace field is a depth migration.
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29. A method as claimed in claim 1, wherein:
a migrated image of a part of the zone to be imaged is formed by using a wave conversion phenomenon, by definition of at least a part of a velocity field in P waves and S waves.
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30. A method as claimed in claim 29, comprising:
using preprocessing to separate seismic events.
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31. A method in accordance with claim 29, wherein:
the migration of a surface composite trace field is a time migration.
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32. A method in accordance with claim 29, wherein:
the migration of a surface composite trace field is a depth migration.
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33. A method in accordance with claim 30, wherein:
the migration of a surface composite trace field is a time migration.
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34. A method in accordance with claim 30, wherein:
the migration of a surface composite trace field is a depth migration.
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35. A method as claimed in claim 1, wherein:
steps a) to g) are used to determine a gradient of a cost function involved in an inverse seismic problem.
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36. A method in accordance with claim 35, wherein:
the migration of a surface composite trace field is a time migration.
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37. A method in accordance with claim 35, wherein:
the migration of a surface composite trace field is a depth migration.
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38. A method in accordance with claim 1, wherein:
the migration of a surface composite trace field is a time migration.
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39. A method in accordance with claim 1, wherein:
the migration of a surface composite trace field is a depth migration.
Specification