WO2017106220A1

WO2017106220A1 - Method for removing interference caused by time overlapping seismic recordings and seismic survey acquisition method associated therewith

Info

Publication number: WO2017106220A1
Application number: PCT/US2016/066435
Authority: WO
Inventors: Bjorn Muller; Troy Thompson
Original assignee: Downunder Geosolutions (America) Llc
Priority date: 2015-12-16
Filing date: 2016-12-14
Publication date: 2017-06-22
Also published as: AU2016370548B2; AU2016370548A1

Abstract

A method for processing seismic data includes entering into a computer signals detected by a plurality of spaced apart seismic sensors resulting from actuating at least one seismic energy source at a plurality of times. The times have a variable interval between successive actuations. The detected signals from each sensor corresponding to each actuation are a trace. The traces from one actuation of the source are selected as an output shot record. Traces corresponding to an actuation prior to the output shot record and traces corresponding to an actuation subsequent to the output shot record are adjusted to a common time reference with the output shot record. Extended traces in the output shot record are generated by appending to the output shot record the adjusted traces from the at least one prior actuation and the at least one subsequent actuation. A random noise filter is applied to the extended traces.

Description

METHOD FOR REMOVING INTERFERENCE CAUSED BY TI ME OVERLAPPING SEISM IC

RECORDINGS AND SEISM IC SURVEY ACQUISITION METHOD ASSOCIATED THEREWITH

Background

[0001] This disclosure relates to the field of seismic surveying of the Earth's subsurface.

More specifically, the disclosure relates to methods for acquiring seismic signals having at least some time overlapping portions between successive actuations of one or more seismic energy sources.

[0002] Geophysical exploration for and exploitation of subsurface hydrocarbon reserves includes the use of seismic surveying. Seismic surveys can be acquired both onshore (land) and offshore (marine). In a marine seismic survey one or more streamers (a streamer being a long cable containing seismic sensors spaced apart along the length of the cable) are towed behind a vessel. A seismic energy source or sources, which may be an air gun array, is also towed behind the same vessel or a different vessel. The seismic energy source is actuated a number of times and upon actuation generates an acoustic signal that propagates downwardly through the water column and into the geological strata beneath the water bottom. The acoustic signal is refracted and reflected from impedance boundaries, which may be associated with boundaries between the various geological formations (or layers). Reflected, refracted and diffracted signals travel back upwardly where they are ultimately detected by the seismic sensors. The seismic sensors may generate electrical or optical signals related to the amplitude of the detected acoustic signals or particle velocity with respect to time. The signals generated by the seismic sensors may be recorded by recording devices of types well known in the art that may be disposed on the vessel; in other implementations the detected signals may be transmitted to a location apart from the vessel and recorded for subsequent processing and analysis.

[0003] The seismic energy source is typically actuated at regular spatial intervals, each such actuation being called a "shot." Such actuation of the seismic energy source takes place while the vessel moves along a selected survey path. The signal recorded with respect to time generated by each seismic sensor in response to actuation of the seismic energy source is known as a seismic "trace." A collection of recorded traces from any subset of or all the seismic sensors along a single streamer for each shot is called a "shot record." The seismic survey is made up of many shot records along a single path traversed by the vessel (called a "sail line") or a plurality of sail lines covering a large area where a plurality of streamers are towed substantially parallel to each other by the vessel or by different vessels and have a known lateral spacing between adjacent streamers. As-recorded shot records may undergo sophisticated processing in order to create a final seismic data volume for interpretation of geophysical characteristics of the formations below the water bottom (or below the ground surface for land based seismic surveys).

[0004] An objective of seismic surveying is to record the response of the earth to seismic signals. As the need to characterize thinner and more complex hydrocarbon reservoirs increases so too does the need for high-resolution seismic data. Resolution of seismic data is related to the bandwidth, or the range of frequencies, that are present in the detected signals. Broader bandwidth seismic data is now in high demand. Many aspects related to the acquisition and the physics of the propagating seismic wavefields act to limit the bandwidth that can be detected by the seismic sensors and then recorded.

[0005] Seismic wavefields, that is, the energy emitted as acoustic (and/or elastic) signals by the seismic energy source, are three-dimensional and propagate through the earth as a function of time and the elastic properties (including the spatial distribution of such properties) of the formations below the ground surface or water surface. Spatial resolution for characterization of elastic properties of the formations in the subsurface or sub bottom is important with respect to sampling the seismic wavefield. The spatial resolution of physical properties determined from the detected seismic signals is related to both the number of and the spacing between the seismic energy sources and seismic sensors. Conventional seismic signal acquisition techniques are arranged to minimize interference between successive shots by using an appropriately large seismic energy source spacing (and thus time interval) between successive shots. To increase spatial resolution it is beneficial to reduce the source (and receiver) spacing. Reducing the source spacing does however result in overlap (in time), or interference, between successive shots, where the signals recorded for any particular shot extend in time beyond the actuation time of the subsequent shot (in the case of continuous recording). The interference is the result of seismic energy from successive shots being recorded at the same time and for a period of time (resulting in a superposition of seismic wavefields). In order for the shots to be processed in a conventional manner this interference must be removed.

[0006] U.S. Patent No. 6,906,981 issued to Vaage et al. describes one method for separating interfering seismic signals where such signals result from actuation of two or more different seismic energy sources. The method disclosed in the Vaage et al. patent requires that shot timing between actuation of one seismic energy source and at least a second seismic energy source is varied in some known, predetermined manner between successive actuations of the first source and at least a second source. The method disclosed in the Vaage et al. patent specifically requires at least two different seismic energy source and further requires pre-determined variations in time delay between successive actuations of the first source and the at least a second source.

[0007] There continues to be a need for seismic data acquisition and processing methods which enable reduced time and/or spacing between successive shots and/or closer seismic sensor spacing so as to improve the spatial resolution of seismic data.

Brief Description of the Drawings

[0008] FIG. 1 shows an example embodiment of acquiring seismic signals which may be processed according to methods described in the present disclosure.

[0009] FIG. 2 shows a portion of signal acquisition and recording components of the acquisition system shown in FIG. 1.

[0010] FIG. 3 shows a simplified example of a conventional shot record for an individual actuation of a seismic energy source and example signals detected by each of a plurality of seismic sensors. [0011] FIG. 4 shows a simplified example of conventional shot records for three successive source actuations.

[0012] FIG. 5 shows a simplified example of three successive shot records wherein detected seismic signals in the shot record result from more than one actuation of a seismic energy source.

[0013] FIG. 6 shows an example of a combination (or "super") shot record for three successive actuations of the seismic energy source displayed on the same trace record.

[0014] FIG. 7 shows a flow chart of an example embodiment of a method according to the present disclosure.

[0015] FIG. 8 shows an example computer system that may be used in some embodiments to perform data processing according to the present disclosure.

Detailed Description

[0016] FIG. 1 shows an example embodiment of a marine seismic data acquisition system which may be used to acquire seismic data for processing according to various aspects of the present disclosure. A seismic vessel 10 moves through a body of water 14, such as a lake or ocean. For purposes of simplifying the explanation which follows, the seismic vessel 10 is shown towing a single seismic sensor streamer 20. In practical embodiments, a plurality of similarly configured streamers may be towed by the vessel 10. In such embodiments, the seismic vessel 10 tows equipment (not shown) adapted to position the streamers at laterally spaced apart locations behind the seismic vessel 10, and substantially in parallel with each other. Such arrangements of streamers, as is known in the art, are typically used for three-dimensional (3D) seismic surveys. However, it should be clearly understood that the number of streamers is not a limitation on the scope of the present disclosure.

[0017] The seismic vessel 10 may include navigation, seismic energy source control, and seismic data recording equipment (referred to for convenience hereinafter collectively as the "recording system") of any type well known in the art and shown generally at 12. The recording system 12 causes at least one seismic energy source 18, which may be towed in the water 14 by the seismic vessel 10, to actuate at various times and/or locations. The seismic energy source ("source") 18 may be any type well known in the art, including air guns, water guns or arrays of such guns. For purposes of describing the various aspects of the present disclosure, the term "source" is intended to mean any individual one or combination of seismic energy sources. The source 18 is shown being towed by the seismic vessel 10, however, in other embodiments, the source 18, or an additional one or more of such seismic energy sources (not shown) may be towed by a different vessel (not shown). In other embodiments, there may be more than one seismic energy source towed from the seismic vessel 10, or another vessel. The actual seismic energy source configuration and number of sources used, and the number and purposes of the particular vessels used are not in any way intended to limit the scope of methods according to the present disclosure.

[0018] The streamer 20 includes seismic sensors 22 disposed at spaced apart positions along the streamer 20. Each of the seismic sensors 22 can include a sensor that is responsive to the pressure in the water 14, or to changes in such pressure (such as change in pressure with respect to time). As is well known in the art, the pressure responsive sensor may be a hydrophone, which generates an electrical or optical signal related to the pressure or a signal related to changes therein. The type of the seismic sensors 22 actually used in any acquisition system is not intended to limit the scope of the present disclosure.

[0019] During seismic data acquisition, the recording system 12 may cause the source 18 to be actuated at selected spatial positions. When the source 18 is actuated, seismic energy travels outwardly from the source 18, generally downwardly (but in fact in all directions), at 24. Some of the downwardly traveling energy 24 reflects from impedance boundaries, including the water bottom 28 and sub-bottom formation layer boundaries (not shown in FIG. 1). Seismic energy may be reflected from the impedance boundary(ies) 28, whereupon the reflected energy travels upwardly, as shown generally at 26. The upwardly traveling seismic energy 26 is detected by the seismic sensors 22 on the streamer 20. [0020] FIG. 2 shows certain components of the acquisition system of FIG. 1 in more detail so that description of methods of processing recorded seismic signals may be better understood. The recording system 12 may include, as previously explained, a source controller 12A which generates signals transmitted to the source 18 at various times. In the present example embodiment, those times may be chosen so that the source 18 is actuated at substantially even distance intervals between successive actuations as will be further explained below. When the actuation signals are transmitted to the source 18, components in the source 18 cause the source to "fire" or discharge energy into the water (14 in FIG. 1). In embodiments of a source 18 such as an air gun, the actuation signal operates electro-mechanical devices in the source 18, such as a solenoid operated pneumatic valve, which causes other components in the source to discharge pressure (e.g., air or water) stored in a chamber. The discharge of such pressure may be used to move a shuttle or similar device to actuate a switch (not shown separately) to send an actuation signal back to the recording system 12. Thus, the actual time of discharge of energy by the source 18 may be measured precisely notwithstanding any electromechanical latency in the components of the source 18. An example of an air gun having the above described components and which explains the relationship between the actuation signal and the actual firing time signal is described in U.S. Patent No. 4,472,794 issued to Chelminski.

[0021] In the present example embodiment, the actuation times for the seismic energy source 18 may be chosen so that the source 18 is actuated on a substantially regular distance (spacing) between successive actuations, e.g., every 12.5 meters. In order to actuate the seismic energy source 18 at substantially equal spacing between successive actuations, it is required to predict when to actuate the source 18 based on factors such as the vessel speed and navigational data, among other factors. Such predictions may not be precise and may result in a random and variable time interval between successive actuations of the source 18. The foregoing two examples of actuating a source such that random and variable time interval occurs between successive actuations of the source are only provided to illustrate methods according to the present disclosure. It is only necessary for purposes of methods of the present disclosure to have a variable time interval between successive actuations of the source. The particular method of actuating the source so that a variable time interval occurs between successive actuations of the source is not intended to limit the scope of the present disclosure.

[0022] Signals generated by the seismic sensors 22 (only one of which is shown in FIG. 2 for clarity of the illustration) may be conducted to an analog to digital converter (ADC) 29, and then to a signal recorder 12B for making a record with respect to time of the signals detected by each of the seismic sensors 22. Various embodiments of the recording system may include any number of ADCs 29 and such ADCs may be multiplexed to digitize signals from more than one seismic sensor 22 or there may be one ADC 29 for each seismic sensor 22. The hardware configuration used for signal recording is not intended to limit the scope of the present disclosure. In any embodiment, however, the actuation time of the source 18 as communicated to the recording system 12 by the signal generated in the source 18 is known and is recorded by the signal recorder. Contemporaneously, signals detected by each of the seismic sensors 22 are digitized, recorded indexed with respect to time. In some embodiments, the recording may be continuous, that is, there is no interruption in recording between successive actuations of the source 18.

[0023] Methods according to the present disclosure make use of variations of the time interval between successive actuations of the source 18. According to one aspect of a method according to the present disclosure there is provided a procedure for removing interfering seismic energy resulting from the recording of seismic signals from different sources or different actuations of the same source sufficiently close in spacing wherein there is interference between the recordings of signals produced by different source actuations. A result of methods according to the present disclosure is to produce shot records where the seismic energy in each resulting shot record is that from just a single source actuation. Different sources may be, for example, different air gun arrays towed by a vessel such as shown at 10 in FIG. 1 or by another vessel, or any other seismic energy source. [0024] Referring to FIG. 3, a schematic representation of a shot record acquired by a single actuation of a seismic energy source is shown. The coordinate (X) axis of the shot record in FIG. 3 represents the sensor from which signals have been recorded. The ordinate (Y) axis represents time, with the actuation time of the source generally being referenced to zero (to). As will be appreciated by those skilled in the art, an actual shot record presented in the manner of the schematic in FIG. 3 would include individual signal records with respect to time from each individual seismic sensor (22 in FIG. 1). Such individual records are referred to as "traces." For purposes of explaining methods according to the present disclosure, it is not necessary to show the individual traces, but only to show features that may be expected to be observable in each trace in a shot record. In FIG. 3, energy traveling directly through the water (14 in FIG. 1) from the source (18 in FIG. 1) to each sensor (22 in FIG. 1), i.e., the "direct arrival", may be observed as a line 30 representative of a high amplitude event in each trace. The time of the direct arrival may be expected to increase linearly with respect to distance between the source (18 in FIG. 1) and each sensor (22 in FIG. 1). A curve 32 may also be observed in FIG. 3 representing the arrival time with respect to distance between the source and each sensor of reflected seismic energy from the water bottom (28 in FIG. 1). Reflected seismic energy from an impedance boundary below the water bottom (28 in FIG. 1) may be observed as a curve 34 in FIG. 3.

[0025] FIG. 4 shows schematic presentations of three successive shot records acquired such that there is substantially no energy from any other actuation of the source in the shot record corresponding to a source actuation for which the shot record is displayed. In FIG. 4, the center shot record (Shot n) is one for which an output shot record is to be generated using a method according to the present disclosure. One immediately preceding shot record is indicated by "Shot n - 1" and one immediately following shot record is indicated by "Shot n + 1." In FIG. 4, the individual shot records are obtained such that each shot record includes in its recorded seismic signals energy that results only from the actuation of the seismic energy source associated with the particular shot record. The same features as explained with reference to FIG. 3, namely the direct arrival, water bottom reflected arrival and sub bottom reflected arrival are also observable in the three shot records shown in FIG. 4.

[0026] FIG. 5 shows schematic representations of shot records made, in the present example embodiment, by actuating the seismic energy source (18 in FIG. 1) such that within the recording time interval of the shot record, energy resulting from prior and later actuations of the seismic energy source may be observed. Such energy may be referred to as interfering energy. For shot record Shot n - 1 in FIG. 5, the direct arrival 30A, water bottom reflection arrival 32A and sub bottom reflection arrival 34A may be observed. The actuation record for Shot n- 1 may take place at a time prior to the actuation record for Shot n. In the referenced shot record, the direct arrival energy from the succeeding actuation (Shot n) may be observed at 30B and the water bottom reflection arrival may be observed at 32B. The recording time interval associated with Shot n -1 shown in FIG. 5 may be shorter than would enable observation of sub bottom reflections resulting from actuation of the source at Shot n. In a schematic representation of the shot record for Shot n, that is, the actuation of the source immediately following Shot n - 1, some of the reflected arrivals from Shot n - 1 and some arrivals from Shot n + 1 may be observed. Similarly, in the schematic representation of the shot record for the source actuation following Shot n, that is, Shot n + 1, some energy resulting from Shot n may be observed.

[0027] Referring to FIG. 6, in example embodiments of a method according to the present disclosure, at least three (and in other embodiments five, seven or more) successive shot records may be merged to form a single continuous extended shot record, which may be referred to as a "super-shot" record. A super-shot record is created for every required output shot record (which will typically be every input shot record, referred to as Shot n in FIG. 5), by merging the output shot record with at least one previous shot record (Shot n - 1 in FIG. 5) and at least one subsequent shot record (Shot n + 1 in FIG. 5), respectively. Such merging creates a data set that is two to three (or more) times as extensive in time. [0028] As explained previously with respect to FIG. 1, individual actuations of the seismic energy source(s) may not occur, and frequently do not occur at precise increments of the recording sample interval, that is at a time corresponding to an integer multiple of the digital sampling rate of the ADC (29 in FIG. 2). In the present example embodiment, traces from the prior shot record(s) and the subsequent shot record(s) may be resampled to the time sample grid of the output shot record to ensure a seamless merge of the individual shot records that make up the super-shot record. In other embodiments, the traces from the prior actuation(s) and the subsequent actuations(s) may be shifted in time to a common time reference with the output shot record prior to appending to the output shot record. Forming the appended shot records is important with respect to processing very low frequencies during the shot interference removal process (negating any low frequency edge effects on the output shot). Each super-shot record thus contains the desired output shot record and energy from a number of interfering shots that result from actuation of the seismic energy source both before and after the output shot respectively.

[0029] While shot records are a common way to represent recorded, unprocessed seismic data, one can also equivalently regard the entire data set as a unitary, multi-dimensional volume of seismic signal traces. The creation of such super-shot records means that every trace in the unitary, multi-dimensional volume is now much longer and contains energy from the both the output shot and interfering shots.

[0030] Random noise suppression filtering, for example, rank reduction filtering, or in some example embodiments multi-dimensional Cadzow filtering may then be used to remove the interfering shot energy. The random noise filtering may be performed simultaneously in up to four dimensional space (three spatial dimensions and time) which greatly improves the process ability to discriminate between signal (i.e., the output shot record) and noise (i.e., the interfering shots). The spatial dimensions may be chosen so that in each spatial dimension the interfering shot energy will appear as random noise. The super shot volume may also be normal moveout ("NMO") corrected prior to rank reduction filtering using the appropriate velocity for the output shot record. The appropriate velocity model for the output shot may be extrapolated to the additional time range in the super-shot record. MO correction using the velocity appropriate for the output shot record increases the randomness of the interfering shot energy (relative to the output shot record) in the multi-dimensional space.

[0031] In considering how to choose the spatial dimensions for random noise suppression filtering such as Cadzow filtering, there are a number of ways one can uniquely define each acquired trace in a seismic survey. Generally speaking, a trace is defined by four spatial coordinates, namely two spatial coordinates (x, y) for the source location and two spatial coordinates of the seismic sensor location. For example, each pair of spatial coordinates could be defined in terms of a unique UTMX, UTMY location on the surface of the earth or defined in terms of an inline and crossline distance with respect to a selected reference location which provide a unique location within the local coordinate system of the particular survey. Each trace also has a fifth dimension which is (recording) time.

[0032] One can thus think of the super-shot volume as a 5D space having four spatial dimensions and one time dimension. There are other commonly used ways to index individual seismic traces. Rather than using the source and sensor locations one could also use common midpoint and common offset, each of which can also be defined by a pair of spatial dimensions.

[0033] The choice of dimensions, and the dimensionality of the space for random noise suppression filtering such as rank reduction filtering, or in the present example embodiment multi-dimensional Cadzow filtering, may be selected based on a number of criteria, which include: including dimensions where the interfering shots appear as random noise; including dimensions where the output shot is well sampled; and including dimensions which are reasonably long (that is have a number of possible values).

[0034] Ultimately the acquisition geometry of the survey in question will indicate the length of various dimensions and how they are sampled. It may be beneficial to choose a 3D or 4D sub-space which may be considered a "slice" of the higher-dimensional data set. It is possible that the interfering shots may appear as signal in more than one dimension, and a slice can be specifically chosen in light of this. The slices can be thought of as affine subspaces (translations of vector subspaces) of the full-dimensional space of data. In general, there will be several suitable vector spaces to choose from, running parallel to the slices, which reduce the number of dimensions in which the interfering shots appear as signal. It may also be beneficial after choosing a particular sub-space, to transform it into a different domain (for example, the tau-p domain) and/or transform the traces to represent a different attribute than amplitude and/or reference the traces to a time other than source actuation (for example, using a moveout correction) before random noise suppression filtering.

[0035] With respect to sampling, if the seismic data as acquired were infinite in extent and continuously sampled, the choice of subspace would make little difference; there are ways to convert a Fourier transform with respect to one coordinate system into a Fourier transform with respect to another. However, in practice, the dimensions of seismic data are finite, and sampled. It is not guaranteed that a Fourier transform of a slice parallel to one vector space can be transformed into a Fourier transform of the same slice with a different coordinate system applied.

[0036] Therefore, each different way of indexing even the same slice of data will capture different information about both the signal (the output shot) and noise (the interfering shots). The output shot record will represent signal of interest no matter how it is viewed, however, the numerical properties of the principal components of the interfering shots will vary with reference to the view. The foregoing is particularly relevant because the random noise suppression filtering, e.g., Cadzow filtering, is not applied to an entire slice, but to windows within the slice (a rectangular window in one coordinate system is a different collection of traces from a rectangular window in another coordinate system). Thus, one may iterate between different multi-dimensional spaces as part of the process to exploit the properties of the signal and noise in different dimensions. For example, in a marine acquisition, dimensions in which the sail line or shot number vary are useful, as in these dimensions the interfering shots will appear as noise. [0037] It may be advisable, due to sampling constraints, to use a multi-dimensional space in which the interfering shots appear as signal in at least one of the spatial dimensions. However, it is known what dimension that is, and this fact can be exploited. For example, one could compare the statistical distributions of various subsets of the Fourier coefficients. For the signal (to be retained) in the output shot record, the distributions will be similar in every direction (isotropic). For the interfering shot energy (to be removed from the output shot record) the distribution in some known direction(s) will be markedly different from the distribution in other directions. This can be exploited when choosing coefficients to damp, by making choices which honor the expected statistics in the various dimensions. This can be framed as an optimization problem.

[0038] Cadzow filtering performs matrix-rank reduction on constant-frequency slices for the purpose of random noise suppression. It is a variant of eigenimage filtering which has been extended to a higher number of dimensions.

[0039] Rank-reduction noise suppression techniques are used in many fields and have many names, including principal component analysis (PCA) and truncated singular-value decomposition (SVD). The simple reason that rank-reduction methods are useful is that signal (i.e., seismic energy which is consistent from trace to trace) will reside in just the first few principal components (or eigenimages) while random noise will be more evenly spread over all eigenimages.

[0040] One possible advantage of using Cadzow filtering is that it can be applied simultaneously in any number of spatial dimensions. The present example implementation of Cadzow filtering may be used in up to four dimensions (time, and up to three spatial dimensions). Application in multi-dimensional space improves the filter process' ability to discriminate between signal and noise. The filter may be expected to work equally well on flat or dipping seismic events, and is exact for noiseless data having a restricted number of dips.

[0041] Another feature of the present example embodiment of a method is that one can produce final output shot records of any length. Once the shot interference removal process is complete, that is, all interfering shot energy has been removed from the super- shot then the super shot can be trimmed to the desired (time) length to create a final output shot record for Shot n. The foregoing process may be repeated for all shot records in a seismic survey.

[0042] A flow chart of an example implementation of a method according to the present disclosure may be better understood with reference to the flow chart in FIG. 7. At 42, after seismic signals have been acquired and recorded as explained with reference to FIG. 1, an input volume may be generated. Such may be performed by using the unprocessed recorded seismic signals and preprocessing, for example, by transcription, inclusion of geodetic position information for the source and sensors at each source actuation time, merging, gain adjustment and types of noise removal processing ordinarily used on seismic signal recordings. At 44, a super shot volume is generated for each intended output shot record. Such super shot volume may be generated by merging signals from one or more source actuations prior to the intended output shot record, and one or more source actuations after the intended output shot record. In the generation of the super shot volume each trace (from the interfering shot records) is resampled onto the time grid (i.e., digital sample interval) of the intended output shot record. At 46, normal moveout ( MO) correction may be applied to each trace in the super shot volume based on MO parameters used to perform NMO correction to the traces in the intended output shots.

[0043] At 48, random noise suppression filtering such as rank reduction filtering, and in an example embodiment multiple dimensional Cadzow filtering, is applied to the traces in a particular sub space(s) of the NMO corrected super shot volume to remove energy from source actuations prior to and after the actuation of the source for which the final shot record is to be produced. Finally, at 50, an output shot record may be generated by limiting the record time of the random noise suppression filtered traces to a selected time interval.

[0044] FIG. 8 shows an example computing system 100 in accordance with some embodiments. The computing system 100 may be an individual computer system 101 A or an arrangement of distributed computer systems. The individual computer system 101A may include one or more analysis modules 102 that may be configured to perform various tasks according to some embodiments, such as the tasks explained with reference to FIGS. 1 through 7. To perform these various tasks, the analysis module 102 may operate independently or in coordination with one or more processors 104, which may be connected to one or more storage media 106. A display device 105 such as a graphic user interface of any known type may be in signal communication with the processor 104 to enable user entry of commands and/or data and to display results of execution of a set of instructions according to the present disclosure.

[0045] The processor(s) 104 may also be connected to a network interface 108 to allow the individual computer system 101 A to communicate over a data network 110 with one or more additional individual computer systems and/or computing systems, such as 10 IB, 101C, and/or 10 ID (note that computer systems 10 IB, 101C and/or 10 ID may or may not share the same architecture as computer system 101 A, and may be located in different physical locations, for example, computer systems 101A and 101B may be at a well drilling location, while in communication with one or more computer systems such as 101C and/or 10 ID that may be located in one or more data centers on shore, aboard ships, and/or located in varying countries on different continents).

[0046] A processor may include, without limitation, a microprocessor, microcontroller, processor module or subsystem, programmable integrated circuit, programmable gate array, or another control or computing device.

[0047] The storage media 106 may be implemented as one or more computer-readable or machine-readable storage media. Note that while in the example embodiment of FIG. 8 the storage media 106 are shown as being disposed within the individual computer system 101A, in some embodiments, the storage media 106 may be distributed within and/or across multiple internal and/or external enclosures of the individual computing system 101A and/or additional computing systems, e.g., 101B, 101C, 101D. Storage media 106 may include, without limitation, one or more different forms of memory including semiconductor memory devices such as dynamic or static random access memories (DRAMs or SRAMs), erasable and programmable read-only memories (EPROMs), electrically erasable and programmable read-only memories (EEPROMs) and flash memories; magnetic disks such as fixed, floppy and removable disks; other magnetic media including tape; optical media such as compact disks (CDs) or digital video disks (DVDs); or other types of storage devices. Note that computer instructions to cause any individual computer system or a computing system to perform the tasks described above may be provided on one computer-readable or machine-readable storage medium, or may be provided on multiple computer-readable or machine-readable storage media distributed in a multiple component computing system having one or more nodes. Such computer-readable or machine-readable storage medium or media may be considered to be part of an article (or article of manufacture). An article or article of manufacture can refer to any manufactured single component or multiple components. The storage medium or media can be located either in the machine running the machine- readable instructions, or located at a remote site from which machine-readable instructions can be downloaded over a network for execution.

[0048] It should be appreciated that the computing system 100 shown in FIG. 8 is only one example of a computing system, and that any other embodiment of a computing system may have more or fewer components than shown, may combine additional components not shown in the example embodiment of FIG. 8, and/or the computing system 100 may have a different configuration or arrangement of the components shown in FIG. 8. The various components shown in FIG. 8 may be implemented in hardware, software, or a combination of both hardware and software, including one or more signal processing and/or application specific integrated circuits.

[0049] Further, the acts of the processing methods described above may be implemented by running one or more functional modules in information processing apparatus such as general purpose processors or application specific chips, such as ASICs, FPGAs, PLDs, GPUs, coprocessors or other appropriate devices. These modules, combinations of these modules, and/or their combination with general hardware are all included within the scope of the present disclosure.

[0050] Throughout the specification, unless the context requires otherwise, the word

"comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Likewise the word "preferably" or variations such as "preferred", will be understood to imply that a stated integer or group of integers is desirable but not essential to the working of methods according to the present disclosure. While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

Claims What is claimed is:

1. A method for processing seismic data, comprising:

entering as input to a computer signals detected by a plurality of spaced apart seismic sensors resulting from actuating at least one seismic energy source at a plurality of times, the plurality of times resulting in a variable time interval between successive actuations, the detected signals from each seismic sensor corresponding to each actuation being a trace;

in the computer, selecting the traces from one actuation of the at least one seismic energy source as an output shot record;

in the computer, adjusting traces corresponding to at least one actuation prior to the output shot record and traces corresponding to at least one actuation subsequent to the output shot record to a common time reference with the output shot record; in the computer, for each trace in the output shot record, generating an extended trace by appending to the output shot record the adjusted traces from the at least one prior actuation and the at least one subsequent actuation; and

in the computer, applying a random noise suppression filter to the extended traces.

2. The method of claim 1 wherein the times are chosen such that the at least one source is actuated at substantially equally spaced apart positions.

3. The method of claim 1 wherein the adjusting traces comprises resampling the traces from the at least one prior actuation and the at least one subsequent actuation to an integer multiple of a digital sample rate of the detected seismic signals.

4. The method of claim 1 further comprising time limiting the filtered extended traces to a selected time interval related to the output shot record.

5. The method of claim 1 wherein the random noise suppression filter comprises a rank reduction filter.

6. The method of claim 5 wherein the rank reduction filter comprises a multi-dimensional Cadzow filter.

7. The method of claim 1 further comprising selecting spatial dimensions for the random noise suppression filter so that in each of or a maximum number of spatial dimensions energy from the at least one prior source actuation and the at least one subsequent source actuation will appear as random noise.

8. The method of claim 7 further comprising, in the computer transforming a domain of the extended traces prior to random noise suppression.

9. The method of claim 1 further comprising, in the computer, applying a moveout correction to the extended traces to change randomness of energy in the extended traces resulting from the at least one prior actuation and the at least one subsequent actuation.

10. The method of claim 9 wherein the moveout correction comprises a normal moveout correction based on a correct velocity for the output shot record to the resampled extended traces.

11. A method for seismic surveying, comprising:

actuating at least one seismic energy source a plurality of times such that a time interval between successive actuations is variable;

detecting seismic signals resulting from each actuation of the at least one seismic energy source by a plurality of spaced apart seismic sensors, the detected signals from each seismic sensor corresponding to each actuation being a trace; in the computer, selecting the traces from one actuation of the at least one seismic energy source as an output shot record;

in the computer, adjusting traces corresponding to at least one actuation prior to the output shot record and traces corresponding to at least one actuation subsequent to the output shot record to a common time reference with the output shot record; in the computer, for each trace in the output shot record generating an extended trace by appending to the output shot record the adjusted traces from the at least one prior source actuation and the at least one source actuation subsequent the actuation; and in the computer, applying a random noise suppression filter to the extended traces.

12. The method of claim 11 wherein the times are chosen such that the at least one source is actuated at substantially equally spaced apart positions.

13. The method of claim 11 wherein the adjusting traces comprises resampling the traces from the at least one prior actuation and the at least one subsequent actuation to an integer multiple of a digital sample rate of the detected seismic signals.

14. The method of claim 11 further comprising time limiting the filtered extended traces to a selected time interval related to the output shot record.

15. The method of claim 11 wherein the random noise suppression filter comprises a rank reduction filter.

16. The method of claim 15 wherein the rank reduction filter comprises a multi-dimensional Cadzow filter.

17. The method of claim 11 further comprising selecting spatial dimensions for the random noise suppression filter so that in each or a maximum number of spatial dimension energy from the at least one prior source actuation and the at least one after source actuation will appear as random noise.

18. The method of claim 17 further comprising, in the computer transforming a domain of the extended traces prior to random noise suppression.

19. The method of claim 11 further comprising, in the computer, applying a moveout correction to the extended traces to change randomness of energy in the extended traces resulting from the at least one prior actuation and the at least one subsequent actuation.

20. The method of claim 19 wherein the moveout correction comprises a normal moveout correction based on a correct velocity for the output shot record to the resampled extended shot record.