Zero-offset seismic trace construction
Described are methods for obtaining seismic signals representative of properties of the earth's interior, including the steps of obtaining near-field acoustic signals recorded in the vicinity of a seismic source ( 13 ), muting from the near-field acoustic signals at least partly signals representing direct arrivals from the seismic source ( 13 ), and using a remaining part of the obtained signals as estimate of a zero-offset data set. The zero-off set data set can then be used to interpolate data from conventional acquisition location, such as streamers ( 11 ), to locations closer to the source ( 13 ).
1. A method of obtaining seismic signals representative of properties of the earth's interior, including the steps of
obtaining near-field acoustic signals recorded in the vicinity of a seismic source, wherein the near-field acoustic signals comprise a combination of signals generated by seismic source and seismic signals generated by reflections of the signals generated by the seismic source from a sea bed and sub-surface structures;
muting at least partly signals representing direct arrivals from the seismic source;
identifying a zero-offset data set in the obtained near-field acoustic signals, wherein the zero offset data set comprises a remaining part of the obtained near-field acoustic signals after the direct arrivals are removed from the near-field acoustic signals; and
using the zero-offset data set for at least one of extrapolating data sets from other locations and interpolating data between the zero-offset data set and non-zero-offset data sets.
2. The method of claim 1 , wherein the time length of the data set exceeds 1 second.
3. The method of claim 1 , wherein the time length of the data set exceeds 2 seconds.
4. The method of claim 1 , wherein the identifying a zero-offset data set in the obtained near-field acoustic signals comprises determining an onset of zero-offset data in near-field acoustic signals.
5. The method of claim 1 , further including the step of deconvolving the remaining part of the obtained signals with a far-field source signature.
6. The method of claim 1 , further including the step of shaping the remaining part of the obtained signals in a signal processing step such that characteristics of the near-field receivers are matched with characteristics of receivers used to obtain non-zero-offset data sets.
7. The method of claim 6 , wherein the signal processing step includes amplitude matching to match amplitudes of the near-field receivers to amplitudes of receivers used to obtained non-zero-offset data sets.
8. The method of claim 6 , wherein the signal processing step includes matching the impulse response of the near-field receivers to the impulse response of receivers used to obtained non-zero-offset data sets.
9. The method of claim 6 , wherein the signal processing step includes matching a sampling rate of the zero-offset data set to a sampling rate of the non-zero-offset data sets.
10. The method of claim 1 , further comprising determining spatial derivatives of the near-field acoustic signals.
11. The method of claim 10 , further comprising determining gradients of the near-field acoustic signals.
12. The method of claim 1 , further comprising the step of using spatial derivatives of the near-field acoustic signals in the interpolation step.
13. The method of claim 12 , comprising the step of interpolating data between the zero-offset data set and non-zero-offset data sets and further comprising the step of using first order and/or higher order spatial derivatives in the interpolation step.
14. The method of claim 1 , comprising the step of extrapolating zero-offset data set and non-zero-offset data sets to an equal depth.
15. The method of claim 1 , comprising the step of processing the zero-offset data set and non-zero data sets to generate a representation of the interior of the earth.
16. The method of claim 1 , comprising the step of comparing the zero-offset data set with zero-offset data set derived though methods selected from a group consisting of stack, DMO-stack or other processing methods.
17. The method of claim 1 , comprising the step of comparing the zero-offset data set and/or data sets derived through interpolation with data sets derived though methods selected from a group consisting of stack, DMO-stack or other processing methods.