Methods and systems that determine a velocity wavefield from a measured pressure wavefield
First Claim
1. In a process for generating an image of a subterranean formation using marine seismic techniques in which one or more sources are activated to generate acoustic energy that is reflected from the subterranean formation and recorded as pressure data by pressure sensors located in one or more streamers, the specific improvement comprising:
- computing an approximate frozen free-surface profile of a free surface above a streamer based on pressure data generated by pressure sensors located at receiver locations along the streamer, the pressure data represents the measured pressure wavefield;
computing reflectivity and normal derivative of the reflectivity at the receiver locations based on the approximate frozen free-surface profile;
computing a normal derivative of the measured pressure wavefield at the receiver locations based on the reflectivity and the normal derivative of the reflectivity at the receiver locations;
computing an approximate normal-velocity wavefield at the receiver locations along the streamer based on the normal derivative of the measured pressure wavefield at the receiver locations, the approximate normal-velocity wavefield does not include low-frequency, streamer vibrational noise; and
generating an image of the subterranean formation based at least in part on the measured pressure wavefield and the approximate normal-velocity wavefield.
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Accused Products
Abstract
Methods and systems that compute an approximate vertical-velocity wavefield based on a measured pressure wavefield and knowledge of the free-surface shape when the pressure wavefield was measured are described. The measured pressure wavefield is used to compute an approximate frozen free-surface profile of the free surface. The approximate frozen free-surface profile and the measured pressure wavefield are then used to compute an approximate vertical-velocity wavefield that does not include low-frequency streamer vibrational noise. The approximate vertical-velocity wavefield and measured pressure wavefield may be used to separate the pressure wavefield into up-going and down-going pressure wavefields.
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Citations
29 Claims
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1. In a process for generating an image of a subterranean formation using marine seismic techniques in which one or more sources are activated to generate acoustic energy that is reflected from the subterranean formation and recorded as pressure data by pressure sensors located in one or more streamers, the specific improvement comprising:
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computing an approximate frozen free-surface profile of a free surface above a streamer based on pressure data generated by pressure sensors located at receiver locations along the streamer, the pressure data represents the measured pressure wavefield; computing reflectivity and normal derivative of the reflectivity at the receiver locations based on the approximate frozen free-surface profile; computing a normal derivative of the measured pressure wavefield at the receiver locations based on the reflectivity and the normal derivative of the reflectivity at the receiver locations; computing an approximate normal-velocity wavefield at the receiver locations along the streamer based on the normal derivative of the measured pressure wavefield at the receiver locations, the approximate normal-velocity wavefield does not include low-frequency, streamer vibrational noise; and generating an image of the subterranean formation based at least in part on the measured pressure wavefield and the approximate normal-velocity wavefield. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A computer system for generating an image of a subterranean formation, the system comprising:
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one or more processors; one or more data-storage devices; and machine-readable instructions stored in one or more of data-storage devices and executed by the one or more processors, the machine-readable instructions directed to computing an approximate frozen free-surface profile of a free surface above a streamer based on pressure data generated by pressure sensors located at receiver locations along the streamer, the pressure data represents the measured pressure wavefield; computing reflectivity and normal derivative of the reflectivity at the receiver locations based on the approximate frozen free-surface profile; computing a normal derivative of the measured pressure wavefield at the receiver locations based on the reflectivity and the normal derivative of the reflectivity at the receiver locations; computing an approximate normal-velocity wavefield at the receiver locations along the streamer based on the normal derivative of the measured pressure wavefield at the receiver locations, the approximate normal-velocity wavefield does not include low-frequency streamer vibrational noise; and generating an image of the subterranean formation based at least in part on the measured pressure wavefield and the approximate normal-velocity wavefield. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 28)
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22. A non-transitory computer-readable medium having machine-readable instructions encoded thereon for generating an image of a subterranean formation and enabling one or more processors of a computer system to perform the operations of
computing an approximate frozen free-surface profile of a free surface above a streamer based on pressure data generated by pressure sensors located at receiver locations along the streamer, the pressure data represents the measured pressure wavefield; -
computing reflectivity and normal derivative of the reflectivity at the receiver locations based on the approximate frozen free-surface profile; computing a normal derivative of the measured pressure wavefield at the receiver locations based on the reflectivity and the normal derivative of the reflectivity at the receiver locations; computing an approximate normal-velocity wavefield at the receiver locations along the streamer based on the normal derivative of the measured pressure wavefield at the receiver locations, the approximate normal-velocity wavefield does not include low-frequency, streamer vibrational noise; and generating an image of the subterranean formation based at least in part on the measured pressure wavefield and the approximate normal-velocity wavefield. - View Dependent Claims (23, 24, 25, 26, 27, 29)
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Specification