Velocity model building for seismic data processing using PP-PS tomography with co-depthing constraint

1. A method for seismic exploration processing seismic data acquired with multicomponent receivers over a subsurface, the method jointly inverting depth migrated primary wave (P) seismic reflection data (PP data) and depth migrated shear wave (S) seismic reflection data (PS data) by:

picking P and S horizons, P and S residual moveouts (RMOs) and P and S dips for the depth-migrated PP and PS data;

performing a kinematic de-migration of the picked P and S horizons, P and S RMOs and P and S dips to calculate P and S horizon invariants and PP and PS RMO invariants;

performing a kinematically forward modelling inversion of:

the PP and PS data using the PP and PS RMO invariants and the P and S horizon invariants to predict PP and PS RMO values, and

PP-PS co-depthing data based on one or more image co-depthing constraints to calculate co-depthing mismatches;

calculating a cost function based on the predicted PP and PS RMO values and the co-depthing mismatches;

updating the P- and S-velocity models simultaneously to minimize the cost function; and

detecting presence of oil and/or gas in the subsurface using an image generated based on the updated P- and S-velocity models.

2. The method of claim 1 , wherein the one or more image co-depthing constraints includes reflectors co-depthing.

3. The method of claim 1 , wherein the one or more image co-depthing constraints includes a volumetric constraint based on Vp/Vs discrepancies between pseudo-observed Vp/Vs values and model values for reflectors in the subsurface.

4. The method of claim 1 , wherein the one or more image co-depthing constraints includes a reflector constraint which minimizes discrepancies between kinematically re-migrated seismic reflectors in PP and PS domains.

5. The method of claim 1 , wherein the updating of the P- and S-velocity models simultaneously comprises:

performing a linear update of multi-layer velocity attributes so as to minimize the cost function; and

repositioning at least one of the P or S horizons corresponding to the at least one of P or S horizon invariants using the updated multi-layer velocity attributes.

6. The method of claim 5 , wherein the performing of the kinematic de-migration, the performing of the kinematically forward modelling inversion, the calculating of the cost function, and the updating of the P- and S-velocity models simultaneously are iterated as part of an update loop until an exit criterion is satisfied.

7. The method of claim 6 , wherein the image is generated based on the updated P- and S-velocity models by:

outputting final pre-stack depth migrated seismic data using the updated P- and S-velocity models when the exit criterion is satisfied; and

generating the image of the subsurface using the final pre-stack depth migrated seismic data.

8. The method of claim 6 , wherein the exit criterion is the P and S RMOs be minimized.

9. A computer system for seismic exploration processing seismic data, the computer system comprising:

an interface configured to receive seismic data acquired with multicomponent receivers over a subsurface; and

at least one processor configured to jointly invert depth migrated primary wave (P) seismic reflection data (PP data) included in the seismic data and depth migrated shear wave (S) seismic reflection data (PS data) included in the seismic data by:

picking P and S horizons, P and S residual moveouts (RMOs) and P and S dips for the depth-migrated PP and PS data;

performing a kinematic de-migration of the picked P and S horizons, P and S RMOs and P and S dips to calculate P and S horizon invariants and PP and PS RMO invariants;

performing a kinematically forward modelling inversion of:

the seismic data using the P and S horizon invariants to predict PP and PS RMO values, and

PP-PS co-depthing data based on one or more image co-depthing constraints to calculate co-depthing mismatches;

calculating a cost function based on the predicted PP and PS RMO values and the co depthing mismatches;

updating the P- and S-velocity models simultaneously to minimize the cost function; and

detecting presence of oil and/or gas in the subsurface using an image generated based on the updated P- and S-velocity models.

10. The system of claim 9 , wherein the one or more image co-depthing constraints includes reflectors co-depthing.

11. The system of claim 9 , wherein the one or more image co-depthing constraints includes a volumetric constraint based on Vp/Vs discrepancies between pseudo-observed Vp/Vs values and model values for reflectors.

12. The system of claim 9 , wherein the one or more image co-depthing constraints includes a reflector constraint which minimizes discrepancies between kinematically re-migrated seismic reflectors in PP and PS domains.

13. The system of claim 9 , wherein the at least one processor is configured to update the P- and S-velocity models simultaneously by:

performing a linear update of multi-layer velocity attributes so as to minimize the cost function; and

repositioning the at least one of P or S horizons corresponding to the at least one of P or S horizon invariants using the updated multi-layer velocity attributes.

14. The system of claim 9 , wherein the at last one processor is configured to repeat the performing of the kinematic de-migration, the performing of the kinematically forward modelling inversion, the calculating of the cost function, and the updating of the P- and S-velocity models simultaneously as part of an update loop until an exit criterion is satisfied.

15. The system of claim 14 , wherein the at least one processor is further configured to update the output final pre-stack depth migrated seismic data when the exit criterion is satisfied; and wherein the at least one processor and the interface are configured to generate the image of the subsurface using the final pre-stack depth migrated seismic data.

16. The system of claim 14 , wherein the exit criterion is the P and S RMOs be minimized.