Patent Application
20140297189
Embodiments of the subject matter disclosed herein generally relate to methods and systems for seismic data processing and, more particularly, to mechanisms and techniques for improving 4D repeatability and/or 3D stability of seismic features related to individual shots or a set of shots.
Marine-based seismic data acquisition and processing techniques are used to generate a profile (image) of a geophysical structure (subsurface) of the strata underlying the seafloor. This profile does not necessarily provide an accurate location for oil and gas reservoirs, but it may suggest, to those trained in the field, the presence or absence of oil and/or gas reservoirs. Thus, providing an improved image of the subsurface in a shorter period of time is an ongoing process.
The acquisition of data in marine-based seismic methods usually produces different results in source strength and signature based on differences in acquisition configuration and sub-surface conditions. Further data processing and interpretation of seismic data can be improved when the data collection methods produce results with the greatest degree of repeatability. For example, determining during an acquisition survey that a problem has developed that will degrade the results of the acquisition survey by generating imaging with a low degree of repeatability is important to producing the highest quality seismic imaging.
Recently, so-called 4D or time-lapse surveys have become an important addition to the product offerings of seismic survey companies. In 4D surveys, a first survey (or one vintage) taken at a first time operates as a baseline to indicate the potential presence/absence of hydrocarbon deposits in a given area. A second survey (or another vintage), taken later, operates to indicate the potential presence/absence of hydrocarbon deposits in the same geographical area, e.g., after removal of the hydrocarbons has occurred. By comparing the two surveys, a 4D picture (where time is the fourth dimension) can be developed which can be used for a number of purposes, e.g., to determine the continued viability of a hydrocarbon field or where to drill for example. However, in order for a 4D survey to be accurate, the first and second surveys need to be performed in a very similar manner, e.g., shot position, receiver position, and other important parameters for a seismic survey. This gives rise to a need to make surveys highly repeatable and to determine when subsequent surveys are not accurate repetitions of an earlier baseline survey.
Attempts have been made to detect, and correct for, seismic acquisitions having unacceptable repeatability characteristics using illumination maps. However, these attempts have been unable to associate the shot position with the unacceptable repeatability characteristics, thus preventing the system from being able to reshoot only those locations where repeatability issues have occurred.
The seismic data acquired by the receivers (sensors on towed streamers or nodes) should be released from the source wave field variability in order to correctly restore quantitative features related to the subsurface properties. Hence, during the seismic acquisition it is important to control the stability of the source signal to ensure the quality of seismic recordings. The source signature stability is therefore important for both 3D and 4D surveys, to ensure that there are no artificial variations that could be interpreted as variations in the subsurface geology or reservoir state.
Accordingly, it would be desirable to provide systems and methods to monitor such information and avoid the afore-described problems and drawbacks by providing the ability to quickly determine if shot are within acceptable repeatability and stability limits.
These, and other, aspects associated with seismic survey quality control are attained by embodiments described herein which include the generation of a multi-criteria shot indicator which indicates the repeatability and/or stability of one or more shots in a seismic survey. The multi-criteria shot indicator be formed using two or more mono-indicators, e.g., each of which is associated with a different shot quality parameter.
According to an embodiment, a method for generating a multi-criteria shot indicator associated with repeatability of a seismic acquisition includes the steps of generating a plurality of shot indicators wherein the plurality of shot indicators are associated with determining a repeatability of one or more shots, generating a plurality of weighting values associated, respectively, with the plurality of shot indicators, applying the plurality of weighting values to the plurality of shot indicators and generating a plurality of weighted shot indicators; and summing the plurality of weighted shot indicators to generate the multi-criteria shot indicator.
According to another embodiment, a method for generating a multi-criteria shot indicator associated with repeatability or stability of seismic surveying, includes generating a plurality of shot indicators, wherein the plurality of shot indicators are associated, respectively, with determining repeatability or stability of one or more shots and comprise at least two of: a surface geometry indicator, a target illumination indicator, a travel time at target indicator, a source signature indicator and a noise indicator; and combining the plurality of shot indicators to generate the multi-criteria shot indicator.
According to another embodiment, a system for generating a multi-criteria shot indicator based on seismic data includes one or more processors configured to execute computer instructions and a memory configured to store the computer instructions wherein the computer instructions further comprise a shot indicator component for generating a plurality of shot indicators, wherein the plurality of shot indicators comprise at least two of: a surface geometry indicator, a target illumination indicator, a travel time at target indicator, a source signature indicator and a noise indicator; and a summing component for summing the plurality of shot indicators to generate a multi-criteria shot indicator.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:
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. Some of the following embodiments are discussed, for simplicity, with regard to the terminology and structure of generating maps of seismic illumination during marine acquisition. However, the embodiments to be discussed next are not limited to these configurations, but may be extended to other arrangements as discussed later.
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.
According to various embodiments described herein, methods and systems for generating multi-criteria shot indicators are presented which, for example, take into account information associated with the true (i.e., accurate) source and receiver locations, and the complexity of the subsurface. For example, a multi-criteria shot indicator according to embodiments can be a composite of a number of individual shot indicators, e.g., two or more of: a surface geometry indicator, a target illumination indicator, a travel time at target indicator, a source signature indicator and a noise indicator. Individual shot indicators can be weighted prior to their combination to generate a multi-criteria shot indicator. Such methods and systems can, for example, be used in the quality control of the data acquisition and help guide those performing seismic surveys to makes infill decisions during the surveys.
In order to provide some context for the subsequent exemplary embodiments related to multi-criteria shot indicators and quality control using such shot indicators, consider first an example of a marine seismic data acquisition process and system as will now be described with respect to
One or more source arrays 104a,b can also be towed by ship 102, or another ship, for generating seismic waves. Source arrays 104a,b can be placed either in front of or behind the receivers 140, or both behind and in front of the receivers 140. The seismic waves generated by the source arrays 104a,b propagate downward, reflect off of, and penetrate the seafloor, wherein the refracted waves eventually are reflected by one or more reflecting structures (not shown in
The signals recorded by seismic receivers 140 vary in time, having energy peaks that may correspond to reflectors between layers in the subsurface being imaged by the seismic acquisition. In reality, since the sea floor and the air/water are highly reflective, some of the peaks correspond to multiple reflections or spurious reflections that should be eliminated before the geophysical structure can be correctly imaged. As will be appreciated by those skilled in the art, a large number of different data processing techniques can be applied to the raw seismic data to make the image of the subsurface more accurate by removing or reducing the impact of noise and other data that negatively impacts its accuracy. A source array includes a plurality of individual wave sources. An individual wave source may be an air gun, a cluster of air guns or a marine vibrator. Since the dimensions of the source array, including the plurality of individual sources, are comparable with the wavelengths of a generated wave, the wave generated by the source array is directional, i.e., the shape of the wave, or the signature varies with the direction until, at a great enough distance, the wave starts having a stable shape. After the shape becomes stable, the amplitude of the wave decreases inversely proportional to the distance from the source. The region where the signature shape no longer changes significantly with distance is known as the “far-field,” in contrast to the “near-field” region where the shape varies based on the distance from the source. Knowledge of the wave source's far-field signature is desirable in order to extract information about the geological structure generating the detected wave upon receiving the far-field input wave.
In order to estimate the source array's far-field signature, an equivalent notional signature for each individual source may be calculated for each of the guns using near-field measurements (see e.g., U.S. Pat. No. 4,476,553 the disclosure of which is incorporated herein by reference). The equivalent notional signature is a representation of the amplitude of the wave due to an individual wave source as a function of time, the source array's far-field signature being a superposition of the notional signatures corresponding to each of the individual sources. In other words, the equivalent notional signature is a tool for representing the contribution of an individual source to the far-field signature, such that the individual source contribution is decoupled from contributions of other individual wave sources in the source array.
Among other things, the point of the discussion above of
Thus, according to an embodiment, an integrated, normalized 4D-indicator “I” is defined for each shot, or set of shots, as a weighted sum of various indicators qualifying the repeatability/stability of the shot with the equation:
I=Σ
j=0
c
W
j
I
j (1)
where C is the number of repeatability or stability criteria being used in a particular embodiment and is a weight associated with corresponding indicator Ij. Note, however, that according to some embodiments, the summed indicators I0+I1 . . . need not be weighted at all, i.e., each Wj may be equal to 1. As expressed by equation (1) there can, of course be any number of shot indicators which are summed to generate the multi-criteria shot indicator I. There can be any combination of two or more shot indicators selected from a pool of indicators. According to one purely illustrative embodiment, which is described in more detail below, the pool can include five indicators, e.g., indicator can be based on surface geometry, indicator I2 can be based on illumination, indicator I3 can be based on travel time, indicator I4 can be based on source signature and indicator I5 can be based on noise.
Examples of mono-criterion indicators, Ij, and weights, Wj, are presented hereafter for individual shots (or sets of shots) paired between, for example, base and monitor surveys. As will be appreciated by those skilled in the art, 4D seismic surveying refers to the technique of taking one seismic survey of a particular geographical area at a first time (i.e., the baseline survey) and another seismic survey of the same geographical area at a later time (i.e., the monitor survey). The baseline survey and the monitor survey can then be compared for various purposes, e.g., to observe changes in the hydrocarbon deposits in a geographical area which has an active well operating therein. Looking first to indicator I1, this surface geometry indicator is related to the 4D geometrical mismatches in source positions, Δs, and receiver positions Δrj, where k=1 to n (n being the number of receivers within the set of cables or streamers), between base and monitor shots. Various mechanisms for calculating positioning or source mismatch are known to those skilled in the art and, therefore, are not described in further detail herein. The surface geometry indicator also can be evaluated with various metrics calculated using Δs and Δri. One of the most classical methods which can be used as a surface geometry indicator according to an embodiment is the computation of the so-called “minimal ΔS+ΔR distance”. In this method, the distance between base and monitor source positions ΔS and the distance between base and monitor receiver positions ΔR are computed and summed for each trace. The pair of base trace and monitor trace for which the summed distance ΔS+ΔR is minimal is selected and defines the “minimal ΔS+ΔR distance” metric which can be used as the surface geometry indicator. Alternatively, or in combination therewith, other metrics could be computed and used, e.g., metrics which account for trace offsets and azimuths.
The target illumination indicator I2 is, according to an embodiment, related to mismatches in target illumination between base shots and monitor shots. The target illumination indicator I2 can be evaluated, for example, by determining a similarity metric between shot imprints from the baseline and monitor surveys. In this context, a shot imprint can be defined as the target illumination associated with a single acquisition shot. As will be appreciated by those skilled in the art, target illumination refers to the number of source-receiver pairs for which reflections occur at a given point. Thus, a shot imprint shows the summation of illuminations obtained from one source and all of the receivers in the towed streamer array(s). One way to generate the indicator I2 according to an embodiment is to process the shot imprint as images represented by pixels with different intensities, i.e., associated with reflection point locations and either hit count or illumination amplitude. These representations, i.e., current imprints and reference imprints, are then compared using an image registration metric. For more details regarding this type of illumination indicator I2, the interested reader is directed to U.S. patent application Ser. No. 14/102,592, entitled “A Repeatability Indicator Based on Shot Illumination for Seismic Acquisition, filed on Dec. 11, 2013, the disclosure of which is hereby incorporated by reference in its entirety.
Continuing with indicator I3, the travel time indicator is related to the 4D mismatches between travel times recorded for a baseline survey and corresponding travel times for each hit on target in a monitor survey. For example, the travel time indicator I3 can be evaluated from reflection travel times computed on the target for some, or all, of the source-receiver couples in both the baseline and monitor surveys
Next, with respect to indicator I4, the source signature indicator is related to the variability of the source signature with respect to a reference signature. The reference signature can defined either for the current survey for a 3D shot-to-shot stability analysis, or from a base shot signature for a 4D evaluation. The source signature can then be evaluated based on near-field or far-field signatures from various metrics, e.g., NRMS, peak-to-bubble ratio, directivity, etc., as will be appreciated by those skilled in the art.
Continuing next with indicator I5, the seismic noise indicator is related to the seismic noise, e.g., the seismic signal to noise ratio, recorded on the shot or, more characteristically, on the shot-line. Those skilled in the art will appreciate that numerous methods to assess the signal to noise ratio on a seismic shot gather in the frequency bandwidth of interest are known and can be used to calculate indicator I5. In one embodiment, for example, the noise is measured on a time window applied to the seismic traces of the shot gathers, generally before the first arrival of the seismic signals on the top of the seismic gather or at the bottom of the gather where little energy comes from late reflections. The time window for the signal is generally centered around the first arrival signal. Frequency amplitude spectra are then computed on several traces, for both signal and noise time windows, and the signal to noise ratio is computed either for each frequency component or for a given frequency bandwidth. As mentioned earlier, one or more of the summed indicators may (or may not) be weighted to generate the multi-criteria shot indicator according to various embodiments. The weights can be adjusted to allocate more or less importance to each of the repeatability indicators in the summed multi-criteria shot indicator.
For example, and according to one embodiment, additive sensitivity factors can be incorporated based on the equation:
W
j
=f
0
×f
1
×w
i (2)
where f0 defines a sensitivity factor for shot illumination and f1 defines a full fold illumination at the imprint location. Sensitivity factor f0 can be set to a high value if the shot illumination imprint is located on the reservoir area of interest for 4D analysis and can be set low if the shot illumination imprint is not located on the reservoir area of interest. Based on complementary full acquisition illumination analysis, it is possible to characterize the embodiment full-fold illumination at the imprint location. Accordingly, the multi-criteria shot indicator system can set f1 low in the case of strong data redundancy and high in the case of critical coverage.
Based on the foregoing embodiments which describe how to calculate multi-criteria shot indicators, generalized methods for their generation can now be described. Looking now to
Next, at step 204, a plurality of weighting values is generated wherein the weighting values are associated, respectively, with the plurality of shot indicators. Continuing at step 206 of the method embodiment, the plurality of weighting values is applied to the plurality of shot indicators to generate a plurality of weighted shot indicators. An example of a technique for applying a weighting value to a shot indicator is multiplying the shot indicator by the weighting value. It will be appreciated by those skilled in the art that the embodiment of
Next at step 208, the plurality of weighted shot indicators is summed to generate a multi-criteria shot indicator. It should be noted in the exemplary method embodiment of
Looking now to
Next, at step 304, each of the plurality of shot indicators is multiplied by an assigned weighting factor to generate a plurality of weighted shot indicator values. Note that, in this embodiment, the usage of weighting is optional and that step 304 can be omitted. Continuing at step 306, the plurality of weighted shot indicators is summed to generate a multi-criteria shot indicator value. It should be noted that different groups of weighted shot indicators can be summed to generate different multi-criteria shot indicators. Moreover, although not shown in
As will be appreciated from the foregoing discussion, methods for generating multi-criteria shot indicators according to these embodiments may, at least in part, be implemented in software operating on a suitably programmed computing device. A system, with suitable software modules or components, will now be described with respect to
The weighting component 404 provides the capability to generate a plurality of weighting values. As described earlier, the weighting values are associated with the plurality of shot indicators. The summing component 406 provides the capability to apply the weighting values to the shot indicators and to sum the weighted shot indicators to generate a multi-criteria shot indicator. Continuing with the embodiment 400, the output component 408 provides the capability to deliver multi-criteria shot indicators for further processing. It should be noted in the embodiment node 400 that the multi-criteria shot indicators can be delivered locally, i.e., onboard the seismic vessel or to a remote location, i.e., land based, for analysis and decision making.
Another purpose for the weights Wi is to normalize each of the repeatability indicators Ii in the integrated multi-criteria shot indicator in order to make each mono indicator dimensionless to enable the system or algorithm to sum the various dimensionless mono indicators together. This, in turn, enables embodiments to assess the repeatability of a monitor line versus a corresponding base line and to determine whether to accept, as valid, a given monitor line: Stated differently, the weighted, summed multi-criteria shot indicator can be considered to be a cost function. As will be appreciated by those skilled in the art, in mathematical optimization and decision theory, a cost function (or equivalently a loss function) is a function that maps an event, or values of one or more variables, onto a real number which represents a “cost” associated with the event. Optimization approaches then seek generally to minimize the cost function. The multi-criteria shot indicator analysis and decision making process described in the foregoing embodiments can thus be translated into an optimization problem of the cost function (e.g., a minimization of the cost function). Thus, the normalized 4D-indicator “I” described above is not limited to being a weighted sum of various indicators qualifying the repeatability/stability of the shot as shown in equation (1). Instead, it can be also a weighted product or any type of combination of the individual indicators. The form of the cost function generally depends on the method chosen to solve the optimization problem.
Decision making methods per se are known to those skilled in the art and, therefore, are not described in further detail herein. For example, however, in another embodiment, a fuzzy logic approach could be used to the decision making problem so that the individual mono indicators are mixed together in a different way than described above. In such a fuzzy logic embodiment, the mono indicators are mapped into fuzzy variables in order to define ranges of the quality of the 4D repeatability. All of the fuzzy variables corresponding to each mono indicator (e.g., far field source variability, illumination imprint matching, specular travel time misfit, signal to noise, etc.) are then contributing together to a global decision on the quality of the repeatability of the line, which is reached after a de-fuzzification process is performed.
The computing device(s) or other network nodes involved in the integrated multi-criteria shot indicator generation, as set forth in the above described embodiments can be any type of computing device capable of processing and communicating seismic data associated with a seismic survey. An example of a representative computing system capable of carrying out operations in accordance with these embodiments is illustrated in
Data storage unit 532 itself can comprise hard disk drive (HDD) 516 (these can include conventional magnetic storage media, but, as is becoming increasingly more prevalent, can include flash drive-type mass storage devices 524, among other types), ROM device(s) 518 (these can include electrically erasable (EE) programmable ROM (EEPROM) devices, ultra-violet erasable PROM devices (UVPROMs), among other types), and random access memory (RAM) devices 520. Usable with USB port 510 is flash drive device 524, and usable with CD/DVD R/W device 512 are CD/DVD disks 534 (which can be both read and write-able). Usable with diskette drive device 514 are floppy diskettes 537. Each of the memory storage devices, or the memory storage media (516, 518, 520, 524, 534, and 537, among other types), can contain parts or components, or in its entirety, executable software programming code (software) 536 that can implement part or all of the portions of the method described herein. Further, processor 508 itself can contain one or different types of memory storage devices (most probably, but not in a limiting manner, RAM memory storage media 520) that can store all or some of the components of software 536.
In addition to the above described components, system 500 also comprises user console 534, which can include keyboard 528, display 526, and mouse 530. All of these components are known to those of ordinary skill in the art, and this description includes all known and future variants of these types of devices. Display 526 can be any type of known display or presentation screen, such as liquid crystal displays (LCDs), light emitting diode displays (LEDs), plasma displays, cathode ray tubes (CRTs), among others. User console 535 can include one or more user interface mechanisms such as a mouse, keyboard, microphone, touch pad, touch screen, voice-recognition system, among other inter-active inter-communicative devices.
User console 534, and its components if separately provided, interface with server 501 via server input/output (I/O) interface 522, which can be an RS232, Ethernet, USB or other type of communications port, or can include all or some of these, and further includes any other type of communications means, presently known or further developed. System 500 can further include communications satellite/global positioning system (GPS) transceiver device 538, to which is electrically connected at least one antenna 540 (according to an exemplary embodiment, there would be at least one GPS receive-only antenna, and at least one separate satellite bi-directional communications antenna). System 500 can access internet 542, either through a hard wired connection, via I/O interface 522 directly, or wirelessly via antenna 540, and transceiver 538.
Server 501 can be coupled to other computing devices, such as those that operate or control the equipment of ship 102, via one or more networks. Server 501 may be part of a larger network configuration as in a global area network (GAN) (e.g., internet 542), which ultimately allows connection to various landlines.
According to a further exemplary embodiment, system 500, being designed for use in seismic exploration, will interface with one or more sources 104a,b and one or more receivers 140. These, as previously described, are attached to streamers 106, to which are also attached birds 130 that are useful to maintain positioning. As further previously discussed, sources 104 and receivers 140 can communicate with server 501 either through an electrical cable that is part of streamer 106, or via a wireless system that can communicate via antenna 540 and transceiver 538 (collectively described as communications conduit 546).
According to further exemplary embodiments, user console 535 provides a means for personnel to enter commands and configuration into system 500 (e.g., via a keyboard, buttons, switches, touch screen and/or joy stick). Display device 526 can be used to show: streamer 1066 position; visual representations of acquired data; source 104 and receiver 140 status information; survey information; and other information important to the seismic data acquisition process. Source and receiver interface unit 502 can receive the hydrophone seismic data from receiver 140 though streamer communication conduit 548 (discussed above) that can be part of streamer 106, as well as streamer 106 position information from birds 130; the link is bi-directional so that commands can also be sent to birds 130 to maintain proper streamer positioning. Source and receiver interface unit 502 can also communicate bi-directionally with sources 104 through the streamer communication conduit 548 that can be part of streamer 106. Excitation signals, control signals, output signals and status information related to source 4 can be exchanged by streamer communication conduit 548 between system 500 and source 4.
Bus 504 allows a data pathway for items such as: the transfer and storage of data that originate from either the source sensors or streamer receivers; for processor 508 to access stored data contained in data storage unit memory 532; for processor 508 to send information for visual display to display 526; or for the user to send commands to system operating programs/software 536 that might reside in either the processor 508 or the source and receiver interface unit 502.
System 500 can be used to implement the methods described above associated with integrated multi-criteria shot indicator generation according to an exemplary embodiment. Hardware, firmware, software or a combination thereof may be used to perform the various steps and operations described herein. According to an exemplary embodiment, software 536 for carrying out the above discussed steps can be stored and distributed on multi-media storage devices such as devices 516, 518, 520, 524, 534, and/or 537 (described above) or other form of media capable of portably storing information (e.g., universal serial bus (USB) flash drive 526). These storage media may be inserted into, and read by, devices such as the CD-ROM drive 514, the disk drive 512, among other types of software storage devices.
It should be noted in the embodiments described herein that these techniques can be applied in either an “offline”, e.g., at a land-based data processing center or an “online” manner, i.e., in near real time while onboard the seismic vessel. For example, integrated multi-criteria shot indicator generation associated with a given target can be performed at the end of each acquired line during a 4D survey. Integrated shot indicators according to these embodiments provide an easy way to assess simultaneously the repeatability and stability of many parameters (e.g., one scalar indicator is synthetized to assess several criteria). Such embodiments are applicable to any type of seismic acquisition system, e.g., systems using geophones, hydrophones, multi-component receivers, or any other type of receiver device or any combination of receiver devices, any type of source (e.g., multi-level sources), any type of streamer/cable, e.g., horizontal, slanted, curved profile, etc., undershoot or node acquisition.
The disclosed embodiments provide a server node, and a method for multi-criteria shot indicator generation associated with seismic data. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present 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. The methods or flow charts provided in the present application may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor.
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.
The present application is related to, and claims priority from U.S. Provisional Patent Application No. 61/805,266, filed Mar. 26, 2013, entitled “4D-REPEATABILITY SHOT INDICATORS,” to Julie SVAY, Nicolas BOUSQUIE, Cheikh NIANG and Thomas MENSCH, the disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61805266 | Mar 2013 | US |
