Systems and methods for high-resolution imaging using separated wavefields
This disclosure presents computational systems and methods for obtaining high-resolution, three-dimensional seismic images of a region of a subterranean formation using separated up-going and down-going wavefields that include primary and multiple reflections obtained by processing dual-sensor towed streamer seismic data. The inclusion of multiple reflections reduces acquisition footprints in migration of the seismic data. The computational systems and methods produce high-resolution images in a region of a subterranean formation that lies below a body of water. The methods and systems employ a digitally encoded wavefields constructed from a discrete sampling of a two-dimensional slice of a three-dimensional wavefield and stored in one or more tangible, physical data-storage devices.
1. A method for imaging a region of a subterranean formation during a marine survey of the subterranean formation comprising:
activating a seismic source;
after each activation of the source,
receiving pressure wavefields and velocity wavefields from dual sensors of streamers towed by a survey vessel along sail lines of the survey;
performing wavefield separation on the pressure wavefields and the velocity wavefields to generate up-going wavefields and down-going wavefields;
generating a primaries image from the up-going wavefield and a multiples image from the up-going and down-going wavefields; and
stacking the primaries images to generate a sail-line primaries image and the multiples images to generate a sail-line multiples image after traveling each sail line of the survey;
stacking the sail-line primaries images to generate a composite primaries image and the sail-line multiples images to generate a composite multiples image; and
summing the composite primaries image and the composite multiples image to generate a resultant three-dimensional image of the region of the subterranean formation.
2. The method of claim 1 further comprising storing the resultant three-dimensional image in the one or more data storage devices.
3. The method of claim 1 , wherein the velocity wavefield further comprises a vertical velocity wavefield.
4. The method of claim 1 , wherein performing wavefield separation further comprises transforming the pressure wavefields and vertical velocity wavefields from the space-time domain to the wavenumber-frequency domain and performing wavefield separation in the wavenumber-frequency domain.
5. The method of claim 1 , wherein generating the primaries image further comprises applying a cross-correlation function of a down-going source wavefield that approximates a primary wavefield emitted from the source and the up-going wavefield.
6. The method of claim 1 , wherein generating the primaries image further comprises applying a deconvolution function of a down-going source wavefield that approximates a primary wavefield emitted from the source and the up-going wavefield.
7. The method of claim 1 , wherein generating the multiples image further comprises applying a deconvolution function of the up-going wavefield and the down-going wavefield.
8. The method of claim 1 , wherein generating the primaries image and the multiples image further comprises
transforming the up-going and down-going wavefields from a wavenumber-frequency domain to a space-frequency domain; and
extrapolating the up-going wavefields and down-going wavefields with respect to depth in the space-frequency domain.
9. The method of claim 1 , wherein summing the composite primaries image and the composite multiples image further comprises convolving the composite primaries image with a first filter and the composite multiples image with a second filter.
10. The method of claim 1 further comprising post processing the composite primaries image and the composite multiples image to correct for non-uniform receiver or streamer coverage of the subterranean formation during the survey.
11. The method of claim 1 , wherein the sail lines further comprise one of straight sail lines, curved sail lines, circular sail lines, and non-linear sail lines.
12. A computer system for processing seismic data obtained from a marine survey of a subterranean formation, the system comprising:
one or more processors;
one or more data-storage devices; and
a routine stored in one or more of the one or more data-storage devices and executed by the one or more processors, the routine directed to
for each sail line of the marine survey,
for each shot from a seismic source along a sail line,
receiving pressure wavefields and velocity wavefields;
performing wavefield separation on the pressure wavefields and the velocity wavefields to generate up-going wavefields and down-going wavefields; and
generating a primaries image from the up-going wavefield and a multiples image from the up-going and down-going wavefields; and
stacking the primaries images to generate a sail-line primaries image and the multiples images to generate a sail-line multiples image;
stacking the sail-line primaries images to generate a composite primaries image and the sail-line multiples images to generate a composite multiples image;
summing the composite primaries image and the composite multiples image to generate a resultant three-dimensional image of a region of the subterranean formation; and
storing the resultant three-dimensional image in the one or more data-storage devices.
13. The system of claim 12 , wherein the velocity wavefield further comprises a vertical velocity wavefield.
14. The system of claim 12 , wherein performing wavefield separation further comprises transforming the pressure wavefields and vertical velocity wavefields from the space-time domain to the wavenumber-frequency domain and performing wavefield separation in the wavenumber-frequency domain.
15. The system of claim 12 , wherein generating the primaries image further comprises applying a cross-correlation function of a down-going source wavefield that approximates a primary wavefield emitted from the source and the up-going wavefield.
16. The system of claim 12 , wherein generating the primaries image further comprises applying a deconvolution function of a down-going source wavefield that approximates a primary wavefield emitted from the source and the up-going wavefield.
17. The system of claim 12 , wherein generating the multiples image further comprises applying a deconvolution function of the up-going wavefield and the down-going wavefield.
18. The system of claim 12 , wherein generating the primaries image and the multiples image further comprises
transforming the up-going and down-going wavefields from a wavenumber-frequency domain to a space-frequency domain; and
extrapolating the up-going wavefields and down-going wavefields with respect to depth in the space-frequency domain.
19. The system of claim 12 , wherein summing the composite primaries image and the composite multiples image further comprises convolving the composite primaries image with a first filter and the composite multiples image with a second filter.
20. The system of claim 12 further comprising post processing the composite primaries image and the composite multiples image to correct for non-uniform receiver or streamer coverage of the subterranean formation during the survey.
21. The system of claim 12 , wherein the sail lines further comprise one of straight sail lines, curved sail lines, circular sail lines, and non-linear sail lines.
22. A non-transitory computer-readable medium having machine-readable instructions encoded thereon for enabling one or more processors of a computer system to perform the operations of
for each sail line of a marine survey,
for each shot from a seismic source along a sail line,
receiving pressure wavefields and velocity wavefields;
performing wavefield separation on the pressure wavefields and the velocity wavefields to generate up-going wavefields and down-going wavefields; and
generating a primaries image from the up-going wavefield and a multiples image from the up-going and down-going wavefields; and
stacking the primaries images to generate a sail-line primaries image and the multiples images to generate a sail-line multiples image;
stacking the sail-line primaries images to generate a composite primaries image and the sail-line multiples images to generate a composite multiples image;
summing the composite primaries image and the composite multiples image to generate a resultant three-dimensional image of a region of the subterranean formation; and
storing the resultant three-dimensional image in the one or more data-storage devices.
23. The medium of claim 22 , wherein the velocity wavefield further comprises a vertical velocity wavefield.
24. The medium of claim 22 , wherein performing wavefield separation further comprises transforming the pressure wavefields and vertical velocity wavefields from the space-time domain to the wavenumber-frequency domain and performing wavefield separation in the wavenumber-frequency domain.
25. The medium of claim 22 , wherein generating the primaries image further comprises applying a cross-correlation function of a down-going source wavefield that approximates a primary wavefield emitted from the source and the up-going wavefield.
26. The medium of claim 22 , wherein generating the primaries image further comprises applying a deconvolution function of a down-going source wavefield that approximates a primary wavefield emitted from the source and the up-going wavefield.
27. The medium of claim 22 , wherein generating the multiples image further comprises applying a deconvolution function of the up-going wavefield and the down-going wavefield.
28. The medium of claim 22 , wherein generating the primaries image and the multiples image further comprises
transforming the up-going and down-going wavefields from a wavenumber-frequency domain to a space-frequency domain; and
extrapolating the up-going wavefields and down-going wavefields with respect to depth in the space-frequency domain.
29. The medium of claim 22 , wherein summing the composite primaries image and the composite multiples image further comprises convolving the composite primaries image with a first filter and the composite multiples image with a second filter.
30. The medium of claim 22 further comprising post processing the composite primaries image and the composite multiples image to correct for non-uniform receiver or streamer coverage of the subterranean formation during the survey.
31. The medium of claim 22 , wherein the sail lines further comprise one of straight sail lines, curved sail lines, circular sail lines, and non-linear sail lines.