DEVICE AND METHOD FOR MITIGATING SEISMIC SURVEY INTERFERENCE

Abstract

A computing system and method for mitigating, in a first seismic survey, cross-talk generated by a second seismic survey. The method includes performing the first seismic survey with a first survey seismic source driven by a first survey pilot sweep, performing the second seismic survey with a second survey seismic source, simultaneously with the first seismic survey, recording with first survey seismic sensors (i) first survey seismic signals that originate from the first survey seismic source and (ii) second survey seismic signals that originate from the second survey seismic source, selecting another first survey pilot sweep, which has less cross-correlation noise with the second survey seismic signals than the first survey pilot sweep, and continuing the first seismic survey with the another first survey pilot sweep.

Claims

1. A method for mitigating, in a first seismic survey, cross-talk generated by a second seismic survey, the method comprising: performing the first seismic survey with a first survey seismic source driven by a first survey pilot sweep; performing the second seismic survey with a second survey seismic source, simultaneously with the first seismic survey; recording with first survey seismic sensors (i) first survey seismic signals that originate from the first survey seismic source and (ii) second survey seismic signals that originate from the second survey seismic source; selecting another first survey pilot sweep, which has less cross-correlation noise with the second survey seismic signals than the first survey pilot sweep; and continuing the first seismic survey with the another first survey pilot sweep.

2. The method of claim 1, wherein the second survey seismic signals are recorded during a listen phase, when the first survey seismic source is stopped.

3. The method of claim 1, wherein the step of selecting comprises: storing in a memory device, a library including plural first survey pilot sweeps designed for a subsurface being surveyed or a library including sweep parameter settings from which the plural first survey pilot sweeps are calculated.

4. The method of claim 3, further comprising: calculating, for each first survey pilot sweep from the library, an auto-correlation with the second survey seismic signal; and selecting, as the another first survey pilot sweep, that first survey pilot sweep from the library that has the smallest amount of cross-correlation noise with the second survey seismic signals.

5. The method of claim 3, wherein the library includes swept sine waves that are linear and non-linear.

6. The method of claim 3, wherein the library includes swept sine waves that are linear and non-linear and pseudo-random sweeps.

7. The method of claim 1, further comprising: confirming that the recorded first survey seismic signals include interference noise from the second seismic survey.

8. The method of claim 7, further comprising: recording the interference noise while the first survey seismic source is silent; autocorrelating the interference noise; and identifying whether a repeated energy emission in a power spectrum of the autocorrelating interference noise is present.

9. The method of claim 1, wherein the first and second seismic surveys take place simultaneously in adjacent blocks.

10. The method of claim 1, wherein the first survey vibratory source is a marine source.

11. A computing device for mitigating, in a first seismic survey, cross-talk generated by a second seismic survey, the computing device comprising: an interface for receiving (i) first survey seismic signals that originate from a first survey seismic source and (ii) second survey seismic signals that originate from a second survey seismic source, wherein the first survey seismic source is driven by a first survey pilot sweep; and a processor connected to the interface and configured to, select another first survey pilot sweep, which has less cross-correlation noise with the second survey seismic signals than the first survey pilot sweep.

12. The device of claim 11, wherein the second survey seismic signals are recorded during a listen phase, when the first survey seismic source is stopped.

13. The device of claim 11, wherein the processor is further configured to: store in a memory device, a library including plural first survey pilot sweeps designed for a subsurface being surveyed or a library including sweep parameter settings from which the plural first survey pilot sweeps are calculated.

14. The device of claim 13, wherein the processor is further configured to: calculate, for each first survey pilot sweep from the library, an auto-correlation with the second survey seismic signal; and selecting, as the another first survey pilot sweep, that first survey pilot sweep from the library that has the smallest amount of cross-correlation noise with the second survey seismic signals.

15. The device of claim 13, wherein the library includes swept sine waves that are linear and non-linear.

16. The device of claim 13, wherein the library includes swept sine waves that are linear and non-linear and pseudo-random sweeps.

17. The device of claim 11, wherein the processor is further configured to: confirm that the recorded first survey seismic signals include interference noise from the second seismic survey; record the interference noise while the first survey seismic source is silent; autocorrelate the interference noise; and identify whether a repeated energy emission in a power spectrum of the autocorrelating interference noise is present.

18. A non-transitory computer readable medium storing executable codes which, when executed on a computer, makes the computer perform a method for for mitigating, in a first seismic survey, cross-talk generated by a second seismic survey, the instructions comprising: receiving (i) first survey seismic signals that originate from a first survey seismic source and (ii) second survey seismic signals that originate from a second survey seismic source, wherein the first survey seismic source is driven by a first survey pilot sweep; selecting another first survey pilot sweep, which has less cross-correlation noise with the second survey seismic signals than the first survey pilot sweep; and driving the first survey seismic source with the another first survey pilot sweep.

19. The medium of claim 18, further comprising: recording the second survey seismic signals during a listen phase, when the first survey seismic source is stopped.

20. The medium of claim 18, further comprising: storing in a memory device, a library including plural first survey pilot sweeps designed for a subsurface being surveyed or a library including sweep parameter settings from which the plural first survey pilot sweeps are calculated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0025] FIG. 1 illustrates two adjacent marine seismic survey systems;

[0026] FIG. 2 illustrates the cross-talk between two seismic survey systems;

[0027] FIG. 3 illustrates a method for reducing cross-talk noise in a seismic survey

[0028] FIG. 4 illustrates some sub-steps of a step of confirming a noise;

[0029] FIGS. 5A-C illustrate an analysis of a noise record for determining whether the noise record contains significant cross-talk from another seismic survey;

[0030] FIG. 6 illustrates a seismic source array;

[0031] FIG. 7 is a flowchart of a method for reducing cross-talk noise in a seismic survey; and

[0032] FIG. 8 is a schematic diagram of a computing device that implements the methods discussed above.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a marine acquisition system that uses vibratory source elements. However, the embodiments to be discussed next are not limited to such marine environment, but they may be implemented in a land environment or for a configuration in which at least one of the two seismic surveys uses impulsive sources or a mixture of impulsive and vibratory sources.

[0034] Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0035] According to an embodiment, there is a method that allows a first seismic crew to select a pilot signal for use with a marine vibrator array so that the impact of cross-talk from a second crew on data quality is reduced. This method is most appropriate for use where the second crew is also using a marine vibratory source whose source signature is unknown. However, the method may be also adapted to work for impulsive source arrays that use air guns.

[0036] Such a method is illustrated in FIG. 3. According to this method, the first seismic crew detects in step 300 that while performing a marine seismic survey using a first seismic marine vibratory source array, interference from a second survey operating in the area is detected or suspected. This step may be performed on board of the towing vessel, using known methods of quality control of acquired seismic data. In step 302, the method confirms the noise source. This step may include one or more sub-steps as now discussed with regard to FIG. 4. FIG. 4 shows that step 302 may include a step 400 of entering a listen mode during which a noise record is made. During this step, the first survey vessel stops shooting its sources (all the sources are stopped if more than one source vessel is present in the first seismic survey) so that the seismic receivers record signals only from the second seismic survey and other unidentified sources (e.g., marine mammals, earthquakes, passing vessels, etc.). FIG. 5A shows a simulated vibratory emission, originating from the second survey vessel, as measured in a noise record. Note that the signal appears to repeat every T seconds, but the pattern may be masked by some noise. FIG. 5A illustrates a record that captures 4 shots. After seismic signals unrelated to the first seismic survey are collected for a given period of time (e.g., in the order of minutes or tens of minutes), they are analyzed on board of the vessel in step 402. These seismic signals can be considered to make up a noise record 500, because they do not originate from the first survey source array. The analysis of the noise record may include, for example, applying a method of autocorrelation to the noise record. FIG. 5B shows the result 502 of the autocorrelation.

[0037] In step 404, the result 502 of the autocorrelation of the noise record 500 is inspected for determining its power spectrum. More specifically, as illustrated in FIG. 5C, the zero lag central peak of the autocorrelation is windowed and an FFT is computed to analyze its power spectrum. It is noticed in the example in FIG. 5C that the spectral amplitude 504 over the seismic frequency range of interest F1 to F2 exceeds a threshold level 506. Based on this step, it can be confirmed that interference from another seismic survey is indeed present if the autocorrelation (e.g., it shows a repeating emission as in FIG. 5B that is consistent with what might be expected from a vibrator source from another crew and has the amplitude spectrum above a certain threshold as in FIG. 5C). For example, if the noise record includes only signals from marine mammals and passing commercial vessels, that noise will not be repetitive as is the noise generated by a vibratory or impulsive source. In step 406, further analysis may be performed on the noise record and/or autocorrelated noise record data that might help identify the nature of the other crew's pilot signal. This further analysis may include transforming the recorded data into the frequency-time domain, or tau-p domain or other domains, in which a repetition pattern may be observed. In this way, the nature of the other crew's pilot signal may be determined, for example, being a swept sine wave or pseudorandom.

[0038] Returning to FIG. 3, after the method confirms that the noise record is generated by another seismic survey, it advances to step 304 in which one or more candidate pilot sweeps are selected. The pilot sweeps are traditionally generated prior to deploying the seismic acquisition system, as described, for example, in U.S. Pat. No. 8,274,862. These pilot sweeps may be stored on board of the vessel, in a library in a memory. The processor that performs the method selects sequentially each available pilot sweep. The available pilot sweeps cover the same frequency range of interest, i.e., they are designed for the first seismic survey and the subsurface to be surveyed. This library of pilot sweeps may include swept sine waves (linear, non-linear, phase encoded, etc.) or pseudorandom types. Alternatively, the sweep signals may be generated on the spot by generating, for example, a new seed value if it is a random excitation signal that uses a random number generator. If the signal is a sweep, it is possible to just provide the start and end frequencies, the type of function (e.g., linear, log, etc.) and the sweep length. Thus, the library may store not the entire sweep signals, but only sweep parameter settings that are then selected to create the alternate candidate pilot signal.

[0039] The method advances then to step 306 in which the noise record is cross-correlated with the selected pilot sweep. Those skilled in the art would recognize that other mathematical algorithms may be used instead of cross-correlation, for determining a similarity or lack of it between the noise record and the pilot sweep. The results of the similarity between the noise record and the pilot sweep may be quantified and stored in the memory in step 308, after which, in step 310, the method checks whether the last pilot selected from the library has been used in step 306. If the answer is no, the process returns to step 304 to select another pilot sweep. If the answer is yes, the process advances to step 312 to select the pilot sweep that has the smallest amount of cross-correlation noise. This selection step is based on the results stored in step 308.

[0040] Once the pilot sweep that has the smallest amount of cross-correlation noise is confirmed in step 312, the pilot sweep is downloaded into the source controller in step 314. Then, the seismic survey advances using this selected pilot sweep for shooting the sources. At this stage, the system exits the silent mode and enters an active mode, in which the source array(s) become active. The method may also include a step of collecting seismic data with the selected pilot sweep, and analyzing the data to confirm that are no new quality issues (e.g., interference) with the noise generated by the other seismic survey.

[0041] However, if after collecting some seismic data and performing further analysis as described above, it is detected that the interference noise is strong, the method illustrated in FIG. 3 can be repeated for selecting another pilot sweep. Thus, the method of FIG. 3 can be performed during the first survey as many times as necessary, and the pilot sweep that is applied to the source array may be changed as many times as necessary.

[0042] In one embodiment, the method may be modified to determine, during the listen phase, a direction from which the noise is arriving. This can be calculated, for example, in a frequency-waveform domain, i.e., the recorded noise is transformed in the frequency-waveform domain, which indicates the direction from which the noise is arriving. If this noise is confirmed to be repetitive indicating that it originates from a second survey, the method may be configured to continuously determine the direction of the noise and record this information with the seismic data. Then, during the processing phase, the seismic signals arriving from that direction can be muted to remove the noise associated with the second survey. Even if some information regarding the first seismic survey is lost due to the muting, the benefit of removing the noise may offset the lack of seismic data from a certain direction.

[0043] In another embodiment, if the method confirms that the noise is generated by the second survey, the first survey source array may be reconfigured or shot in a certain order to redirect the energy to have a minimal interference with the energy arriving from the second survey.

[0044] As noted above, the methods discussed above may be implemented when both the first and second seismic surveys use vibratory sources, or when the first survey uses vibratory sources and the second seismic survey uses impulsive sources, or even when both surveys use impulsive sources. The methods discussed above are also valid when one or both the first and second survey sources include a combination of vibratory and impulsive source elements.

[0045] To exemplify this concept, FIG. 6 shows a source array 600 that has a float 602 floating at the water surface 620. From the float 602, four source elements 604-610 are suspended. The number of source elements can vary between 3 and 20. The depths of the source elements can also vary. In one embodiment, all source elements 604-610 are vibratory elements. In another element, all source elements are air guns. In still another embodiment, elements 604 and 606 are vibratory elements and elements 508 and 610 are air guns.

[0046] According to an embodiment, a method for attenuating, in a first seismic survey, cross-talk generated by a second seismic survey, is now discussed. The method includes a step 700 of performing the first seismic survey with a first survey seismic source driven by a first survey pilot sweep, a step 702 of performing the second seismic survey with a second survey seismic source, simultaneously with the first seismic survey, a step 704 of recording with first survey seismic sensors first survey seismic signals that originate from the first survey seismic source and second survey seismic signals that originate from the second survey seismic source, a step 706 of selecting an alternate first survey pilot sweep, which has less cross-correlation noise with the second survey seismic signals than the first survey pilot sweep, and a step 708 of continuing the first seismic survey with the alternate first survey pilot sweep.

[0047] Note that the above discussed methods may also be implemented in land seismic surveys that use vibratory sources.

[0048] The above methods and others may be implemented in a computing system specifically configured for seismic acquisition. An example of a representative computing system capable of carrying out operations in accordance with the exemplary embodiments is illustrated in FIG. 8. This computing system may be associated with any of the source controllers that control the sources. Hardware, firmware, software or a combination thereof may be used to perform the various steps and operations described herein.

[0049] The exemplary computing system 800 suitable for performing the activities described in the exemplary embodiments may include a server 801. Such a server 801 may include a central processor (CPU) 802 coupled to a random access memory (RAM) 804 and to a read-only memory (ROM) 806. The ROM 806 may also be other types of storage media to store programs, such as programmable ROM (PROM), erasable PROM (EPROM), etc. The processor 802 may communicate with other internal and external components through input/output (I/O) circuitry 808 and bussing 810, to provide control signals and the like. The processor 802 carries out a variety of functions as are known in the art, as dictated by software and/or firmware instructions.

[0050] The server 801 may also include one or more data storage devices, including a hard drive 812, CD-ROM drives 814, and other hardware capable of reading and/or storing information such as DVD, etc. In one embodiment, software for carrying out the above-discussed steps may be stored and distributed on a CD- or DVD-ROM 816, removable memory device 818 or other form of media capable of portably storing information. These storage media may be inserted into, and read by, devices such as the CD-ROM drive 814, the disk drive 812, etc. The server 801 may be coupled to a display 820, which may be any type of known display or presentation screen, such as LCD, LED displays, plasma displays, cathode ray tubes (CRT), etc. A user input interface 822 is provided, including one or more user interface mechanisms such as a mouse, keyboard, microphone, touchpad, touch screen, voice-recognition system, etc.

[0051] The server 801 may be coupled to other computing devices, such as landline and/or wireless terminals via a network. The server may be part of a larger network configuration as in a global area network (GAN) such as the Internet 828, which allows ultimate connection to various landline and/or mobile client devices. The computing device may be implemented on a vehicle (e.g., vessel or truck) that performs a marine or land seismic survey. In one application, computing system 800 is a dedicated system that is tailored for being deployed on vessel, and also for interacting with the navigation system of the vessel.

[0052] The disclosed exemplary embodiments provide a system and a method for reducing cross-talk produced by one seismic survey in an adjacent seismic survey. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

[0053] Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

[0054] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.