Seismic imaging systems and methods employing tomographic migration-velocity analysis using common angle image gathers

• US 8,406,081 B2
• Filed: 09/25/2009
• Issued: 03/26/2013
• Est. Priority Date: 09/25/2009
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company), Landmark Graphics Corporation (Halliburton Company)
• Original Assignee: Landmark Graphics Corporation (Halliburton Company)
• Inventors: Ren, Yiqing, Jin, Shengwen, Xia, Fan
• Primary Examiner(s): Hellner, Mark
• Assistant Examiner(s): BREIER, KRYSTINE E
• Application Number:
  US12/566,885
• Publication Number:
  US 20110075516A1
• Time in Patent Office: 1,278 Days
• Field of Search: 367/37, 367/38, 367/50, 367/51, 367/53, 367/73, 702/18
• US Class Current: 367/73
• CPC Class Codes: G01V 1/303 for determining velocity profiles or travel times

Abstract

In at least some embodiments, the system obtains shot gathers for a survey region and migrates the shot gather data with an initial velocity model to obtain angle-domain common image gathers. The system processes the common image gathers to determine depth residuals and corresponding angle-dependent time deviations throughout a seismic survey region. The system solves a set of tomographic equations which employ ray theory to establish a relationship between a travel time deviation and the depth residual of a reflector in the depth-offset ray parameter (z,p) domain. The resulting updates are applied to the velocity model and can be used to re-migrate the shot gather data. The system generates a representation of the survey region that can be displayed to a user.

Claims

1. A seismic imaging method that comprises:

obtaining shot gathers for a survey region;

migrating shot gather data with an initial velocity model to obtain angle-domain common image gathers;

determining angle-dependent travel time deviations;

solving a set of tomographic equations that relate the travel time deviations to velocity model updates, wherein said solving includes performing a global least-squares inversion with regularization, subject to geological constraints;

applying the updates to the velocity model; and

displaying a representation of the survey region to a user based at least in part on the updated velocity model.

2. The method of claim 1, further comprising re-migrating the shot gather data using the updated velocity model.

3. The method of claim 2, further comprising repeating said determining, solving, applying, and re-migrating operations until a migration convergence is achieved.

4. The method of claim 1, wherein said determining the angle-dependent travel time deviations comprises:

measuring similarity between common image gathers at different angles to obtain depth residuals Δ

z;

determining a local dip angle α

from the migrated data; and

calculating the angle-dependent travel time perturbations based at least in part on the depth residuals and the local dip angle.

5. The method of claim 4, wherein the angle-dependent travel time perturbations are expressible in the form

Δ

t(p_h)=Δ

z√

{square root over (4S² cos² α

−

p_h²)},

where S is a local slowness value, p_h is an offset ray parameter that includes a dependence on a specular reflection angle θ

.

6. The method of claim 1, wherein the set of tomography equations are based on the relationship:

7. The method of claim 1, wherein said representation of the survey region comprises shot gather data migrated using the updated velocity model.

15. The method of claim 1, further comprising determining the set of tomographic equations based on measuring raypath lengths associated with significant reflectors, and storing the raypath lengths as elements of a sparse Jacobian matrix.

16. The method of claim 1, further comprising specifying a valid ray-tracing dataset for inversion as one of the geological constraints.

17. The method of claim 1, further comprising specifying a maximum or minimum velocity for the velocity model updates as one of the geological constraints.

8. A seismic imaging system that comprises:

at least one storage device that stores shot gathers from a seismic survey of a given survey region;

a memory that stores seismic imaging software; and

at least one processor coupled to the memory to execute the seismic imaging software, wherein the software configures the at least one processor to;

retrieve shot gather data from the storage device;

migrate the shot gather data with an initial velocity model to obtain angle-domain common image gathers;

determine angle-dependent travel time deviations;

solve a set of tomographic equations that relate the travel time deviations to velocity model updates, wherein as part of said solving, the software configures the at least one processor to perform a global least-squares inversion with regularization, subject to geological constraints;

apply the updates to the velocity model; and

display a representation of the survey region to a user based at least in part on the updated velocity model.

9. The system of claim 8, wherein the software further configures the at least one processor to re-migrate the shot gather data using the updated velocity model.

10. The system of claim 9, wherein the software further configures the at least one processor to repeat said determining, solving, applying, and re-migrating operations until a migration convergence is achieved.

11. The system of claim 8, wherein as part of determining the angle-dependent travel time deviations, the software configures the at least one processor to:

measure similarity between common image gathers at different angles to obtain depth residuals Δ

z;

determine a local dip angle α

from the migrated shot gather data; and

calculate the angle-dependent travel time perturbations based at least in part on the depth residuals and the local dip angle.

12. The system of claim 11, wherein the angle-dependent travel time perturbations are expressible in the form

Δ

t(p_h)=Δ

z√

{square root over (4S² cos² α

−

p_h²)},

where S is a local slowness value, p_h is an offset ray parameter that includes a dependence on a specular reflection angle θ

.

13. The system of claim 8, wherein the set of tomography equations are based on the relationship:

14. The system of claim 8, wherein said representation of the survey region comprises shot gather data re-migrated using the updated velocity model.

18. The system of claim 8, wherein the software further configures the at least one processor to determine the set of tomographic equations based on measuring raypath lengths associated with significant reflectors, and to store the raypath lengths as elements of a sparse Jacobian matrix.

19. The system of claim 8, wherein the software further configures the at least one processor to specify a valid ray-tracing dataset for inversion as one of the geological constraints.

20. The system of claim 8, wherein the software further configures the at least one processor to specify a maximum or minimum velocity for the velocity model updates as one of the geological constraints.