Apparatus and method for reconstructing complex salt geometry using dual-flood RTM with prismatic waves

1. A method for processing seismic data acquired to explore an underground formation including a salt body, by a computer, the method comprising:

selecting well-imaged areas of a sediment-to-salt interface from an initial model of the underground formation including an image of the salt body obtained from the seismic data;

performing

(1) a dual-flood reverse-time migration (RTM) with prismatic waves to identify new areas of the sediment-to-salt interface, the new areas being outside the well-imaged areas, and

(2) an RTM to identify other new areas of the sediment-to-salt interface or of a salt-to-sediment interface; and

generating an updated model of the underground formation including an updated image of the salt body using the new areas of the sediment-to-salt interface and the other new areas of the sediment-to-salt interface or of a salt-to-sediment interface,

wherein the well-imaged areas of the sediment-to-salt interface are identified by performing a sediment dual-flood RTM, and the dual-flood RTM with prismatic waves considers at least two reflections, one of which is on the well-imaged areas.

2. The method of claim 1 , the initial model is obtained by applying sediment flood RTM to the seismic data.

3. The method of claim 1 , wherein the RTM is performed repeatedly until the new areas together with the well-imaged areas continuously define the sediment-to-salt interface.

4. The method of claim 1 , wherein the RTM is performed repeatedly until a predetermined criterion related to quality of image of a formation under the sediment-to-salt interface is met.

5. The method of claim 1 , wherein the RTM is any of a salt-flood RTM, a sediment flood RTM, a salt-body RTM or a dual flood RTM.

6. The method of claim 1 , wherein, for the dual-flood RTM with prismatic waves, a first velocity model is used for calculating a first flood, the first velocity model assuming that seismic waves travel only through sedimentary layers, and

a second velocity model is used for calculating a second flood, the second velocity model assuming that there is only salt under the well-imaged areas of the sediment-to-salt interface on which the second flood is reflected before intersecting the first flood,

wherein the first flood and the second flood start one from a source and one from a receiver of seismic waves that cause the seismic data.

7. The method of claim 1 , wherein the prismatic waves are reflected twice between a source and a receiver, being once reflected on the well-imaged areas of a sediment-to-salt interface.

8. A computer-readable medium non-transitory storing executable codes, which, when executed on a computer, make the computer perform a method for processing seismic data acquired to explore an underground formation including a salt body, the method comprising:

selecting well-imaged areas of a sediment-to-salt interface from an initial model of the underground formation including an image of the salt body obtained from the seismic data;

performing

(1) a dual-flood reverse-time migration (RTM) with prismatic waves to identify new areas of the sediment-to-salt interface, the new areas being outside the well-imaged areas, and

(2) an RTM to identify other new areas of the sediment-to-salt interface or of a salt-to-sediment interface; and

generating an updated model of the underground formation including an updated image of the salt body using the new areas of the sediment-to-salt interface and the other new areas of the sediment-to-salt interface or of a salt-to-sediment interface,

wherein the well-imaged areas of the sediment-to-salt interface are identified by performing a sediment-only dual-flood RTM, and the dual-flood RTM with prismatic waves considers at least two reflections, one of which is on the well-imaged areas.

9. The computer-readable medium of claim 8 , wherein the initial model is obtained by applying sediment flood RTM to the seismic data.

10. The computer-readable medium of claim 8 , wherein the RTM is performed repeatedly until the new areas together with the well-imaged areas continuously define the sediment-to-salt interface.

11. The computer-readable medium of claim 8 , wherein the RTM is performed repeatedly until a predetermined criterion related to quality of image of a formation under the salt-to-sediment interface is met.

12. The computer-readable medium of claim 8 , wherein the RTM is any of a salt-flood RTM, a sediment flood RTM, a salt-body RTM or a dual flood RTM.

13. The computer-readable medium of claim 8 , wherein a first velocity model is used for calculating a first flood, the first model assuming that seismic waves travel only through sedimentary layers, and a second velocity model is used for performing a second flood, the second velocity model assuming that there is only salt under the well-imaged areas of the sediment-to-salt interface on which the second flood is reflected before intersecting the first flood, wherein the first flood and the second flood start one from a source and one from a receiver of seismic waves that cause the seismic data.

14. The computer-readable medium of claim 8 , wherein the prismatic waves are reflected twice between a source and a receiver, once being reflected on the well-imaged areas of the sediment-to-salt interface.

15. An apparatus for processing seismic data, the apparatus comprising:

a data interface configured to receive the seismic data and to output image data; and

a data processing unit connected to the interface and configured

to select well-imaged areas of a sediment-to-salt interface from an initial model of the underground formation including an image of the salt body obtained from the seismic data;

to perform (1) a dual-flood reverse-time migration (RTM) with prismatic waves to identify new areas of the sediment-to-salt interface, the new areas being outside the well-imaged areas, and (2) an RTM to identify other new areas of the sediment-to-salt interface or of a salt-to-sediment interface; and

to generate an updated model of the underground formation including an updated image of the salt body using the new areas of the sediment-to-salt interface and the other new areas of the sediment-to-salt interface or of a salt-to-sediment interface,

wherein the well-imaged areas of the sediment-to-salt interface are identified by performing a sediment-only dual-flood RTM, and the dual-flood RTM with prismatic waves considers at least two reflections, one of which is on the well-imaged areas.

16. The apparatus of claim 15 , wherein the data processing unit obtains the initial model by applying sediment flood RTM to the seismic data.

17. The apparatus of claim 15 , wherein the data processing unit performs the RTM repeatedly until the new areas together with the well-imaged areas continuously define the sediment-to-salt interface.

18. The apparatus of claim 15 , wherein the RTM is any of a salt-flood RTM, a sediment flood RTM, a salt-body RTM or a dual flood RTM.

19. The apparatus of claim 15 , wherein the data processing unit uses

a first velocity model for calculating a first flood, the first model assuming that seismic waves travel only through sedimentary layers, and

a second velocity model for calculating a second flood RTM, the second velocity model assuming that there is only salt under the well-imaged areas of the sediment-to-salt interface on which the second flood is reflected, wherein the first flood and the second flood start one from a source and one from a receiver of seismic waves that cause the seismic data.

20. The apparatus of claim 15 , wherein the data processing unit reconstructs the prismatic waves assuming that the waves are reflected twice between a source and a receiver, being once reflected on the well-imaged areas of the sediment-to-salt interface.