Demultiple using up/down separation of towed variable-depth streamer data
Methods and systems for processing data acquired using a variable-depth streamer, obtain up-going and down-going wavefields at a predetermined datum, and use them to identify multiples included in the up-going wavefield. An image of a geological formation under the seabed is then generated using the data from which the multiples have been removed, and/or the multiples.
1. A method for processing recorded data acquired using a variable-depth streamer, the method comprising:
receiving the recorded data acquired using the variable-depth streamer;
applying wavefield separation to the recorded data using a processor, at a locus of the variable-depth streamer, to obtain an up-going wavefield and a down-going wavefield at the locus of the variable-depth streamer;
extrapolating the up-going wavefield and the down-going wavefield from the locus of the variable-depth streamer to a predetermined datum, different from the locus of the variable-depth streamer;
calculating multiples by removing the extrapolated down-going wavefield at the predetermined datum from the extrapolated up-going wavefield at the predetermined datum;
extrapolating the multiples at the locus of the variable-depth streamer;
removing the extrapolated multiples from the up-going wavefield at the locus of the variable-depth streamer to obtain a primary dataset; and
generating an image of a geological formation under the seabed using (1) the primary dataset, and/or (2) the multiples.
2. The method of claim 1 , wherein the predetermined datum is the seabed.
3. The method of claim 1 , wherein the extrapolated up-going wavefield and the extrapolated down-going wavefield at the predetermined datum are obtained using a wavefield separation based on a tau-p model thereof.
4. The method of claim 1 , wherein information on a water velocity dependence on depth is used when extrapolating the up-going wavefield and the down-going wavefield to the predetermined datum.
5. The method of claim 1 , wherein the extrapolated up-going wavefield and the extrapolated down-going wavefield at the predetermined datum are obtained using a sparse inversion method.
6. The method of claim 1 , wherein the calculating of the multiples includes determining a matching filter that minimizes a difference between the extrapolated up-going wavefield and the extrapolated down-going wavefield at the predetermined datum.
7. The method of claim 1 , wherein the calculating of the multiples is an iterative process.
8. The method of claim 7 , wherein the iterative process uses at least two different methods to identify the multiples.
9. The method of claim 1 , wherein the calculating of the multiples includes:
transforming in a spectral domain the extrapolated up-going wavefield and the extrapolated down-going wavefield at the predetermined datum; and
dividing the transformed up-going wavefield to the transformed down-going wavefield.
10. The method of claim 1 , further comprising:
extrapolating the multiples to another datum.
11. The method of claim 1 , further comprising:
migrating the multiples separately from the primary dataset, to another datum.
12. An apparatus for seismic data processing, the apparatus comprising:
an input-output interface configured to receive recorded data acquired using a variable-depth streamer; and
a data processing unit configured
to apply wavefield separation to the recorded data, at a locus of the variable-depth streamer, to obtain an up-going wavefield and a down-going wavefield at the locus of the variable-depth streamer;
to extrapolate the up-going wavefield and the down-going wavefield from the locus of the variable-depth streamer to a predetermined datum, different from the locus of the variable-depth streamer;
to calculate multiples by removing the extrapolated down-going wavefield at the predetermined datum from the extrapolated up-going wavefield at the predetermined datum;
to extrapolate the multiples at the locus of the variable-depth streamer;
to remove the extrapolated multiples from the up-going wavefield at the locus of the variable-depth streamer to obtain a primary dataset; and
to generate an image of a geological formation under the seabed using (1) the primary dataset, and/or (2) the multiples.
13. The apparatus for seismic data processing of claim 12 , wherein the data processing unit is further configured to extrapolate the multiples to another datum before generating the image.
14. The apparatus for seismic data processing of claim 12 , wherein the data processing unit is further configured to extrapolate the primary dataset to the another datum.
15. The apparatus for seismic data processing of claim 12 , wherein the data processing unit is further configured to migrate the primary dataset to the predetermined datum.
16. The apparatus for seismic data processing of claim 12 , wherein the predetermined datum is the seabed.
17. The apparatus for seismic data processing of claim 12 , wherein the data processing unit is configured to obtain the extrapolated up-going wavefield and the extrapolated down-going wavefield at the predetermined datum using a wavefield separation based on a tau-p model thereof.
18. The apparatus for seismic data processing of claim 12 , wherein the data processing unit is configured to obtain the extrapolated up-going wavefield and the extrapolated down-going wavefield at the predetermined datum using a sparse inversion method.
19. A method for exploring a geological formation under the seabed, the method comprising:
receiving data recorded using a variable-depth streamer;
processing the recorded data to generate an image of the geological formation,
wherein the processing includes,
applying wavefield separation to the recorded data, at a locus of the variable-depth streamer, to obtain an up-going wavefield and a down-going wavefield at the locus of the variable-depth streamer, the up-going wavefield and the down-going wavefields at the locus of the variable-depth streamer being derived using an inversion and/or minimization method,
extrapolating the up-going wavefield and the down-going wavefield from the locus of the variable-depth streamer to a predetermined datum, different from the locus of the variable-depth streamer,
calculating multiples based on the extrapolated up-going wavefield and the extrapolated down-going wavefield at the predetermined datum,
extrapolating the multiples at the locus of the variable-depth streamer; and
removing the extrapolated multiples from the up-going wavefield at the locus of the variable-depth streamer to obtain a primary dataset.
20. A non-transitory computer-readable medium configured to store executable codes which when executed by a computer perform a method for processing recorded data acquired using a variable-depth streamer, the method comprising:
receiving the recorded data acquired using the variable-depth streamer;
applying wavefield separation to the recorded data, at a locus of the variable-depth streamer, to obtain an up-going wavefield and a down-going wavefield at the locus of the variable-depth streamer;
extrapolating the up-going wavefield and the down-going wavefield from the locus of the variable-depth streamer to a predetermined datum, different from the locus of the variable-depth streamer;
calculating multiples by removing the extrapolated down-going wavefield at the predetermined datum from the extrapolated up-going wavefield at the predetermined datum;
extrapolating the multiples at the locus of the variable-depth streamer;
removing the extrapolated multiples from the up-going wavefield at the locus of the variable-depth streamer to obtain a primary dataset; and
generating an image of a geological formation under the seabed using (1) the recorded data from which the multiples have been removed, and/or (2) the multiples.