BRPI1102660A2 - Method and apparatus for seismic data double image retrieval - Google Patents

Abstract

METHOD AND APPARATUS TO REMOVE DOUBLE IMAGE OF SEISMIC DATA. The invention relates to a device, computer instructions and a method for double-image seismic data related to a sub-surface of a body of water. The method includes admitting data recorded by detectors that are towed by a vessel, the data being associated with waves moving from the subsurface to the detectors; apply a migration procedure to the data to determine a first image of the sub-surface; apply a mirror migration procedure to the data to determine a second image of the subsurface; join the deconvolution of the first image and the second image to remove the double image of a refectivity of the sub-surface; and generating a final image of the sub-surface based on the reflectivity of double image removal from the deconvolution junction step.

Description

Report of the Invention Patent for "METHOD AND APPARATUS FOR DOUBLE SEISMIC IMAGE WITHDRAWAL".

BACKGROUND TECHNICAL FIELD

The subject matter embodiments disclosed herein generally refer to methods and systems and, more particularly, to mechanisms and techniques for seismic data double imaging. DISCUSSION OF BACKGROUND During the past years, the interest in the development of

New fields of oil and gas production increased dramatically. However, the availability of land-based production fields is limited. Thus, the industry has now extended to drilling in offshore locations that seem to hold a vast amount of fossil fuel. Drilling in the open sea is a costly process. Thus, those engaged in such a costly undertaking invest substantially in geophysical surveys in order to decide more precisely where to drill or not (to avoid a dry well).

The processing and acquisition of marine seismic data generates a profile (image) of the geophysical structure (subsurface) under marine soil. While this profile does not provide an accurate location for oil and gas, it does suggest to those trained in the field the presence or absence of oil and / or gas. Thus, providing a high-resolution subsurface image is an ongoing process for exploring natural sources, including but not limited to oil and / or gas.

During a seismic data acquisition process, as shown in Figure 1, a vessel 10 drags plural detectors 12. The plural detectors 12 are disposed along a cable 14. The cable 14, along with its corresponding detectors 12, are sometimes referred to by those skilled in the art as a pennant 16. Vessel 10 may tow plural streamers 16 at the same time. Streamers may be arranged horizontally, that is, resting at a constant depth Z1 relative to the surface 18 of the ocean. Also, plural streamers 16 may form a constant angle (i.e. streamers may be tilted) with respect to the ocean surface as disclosed in US Patent No. 4,992,992, the total content of which is incorporated herein by reference. Figure 2 shows such a configuration in which all detectors 12 are distributed along a sloping straight line 14 that makes a constant angle α with a horizontal reference line 30.

Referring to Figure 1, vessel 10 also drags a sound source 20 configured to generate an acoustic wave 22a. The acoustic wave 22a propagates downward and penetrates the seabed 24, eventually being reflected by a reflection structure 26 (reflector). The reflected acoustic wave 22b propagates upward and is detected by detector 12. For simplicity, Figure 1 shows only two paths 22a corresponding to the acoustic wave. However, the acoustic wave emitted by source 20 may be substantially a spherical wave, for example, it propagates in all directions from source 20. Parts of reflected acoustic wave 22b (primary) are recorded by the various detectors 12 ( the recorded signals are called dashes), while parts of the reflected wave 22c pass through the detectors 12 and reach the water surface 18. Since the interface between water and air is very close as a near-perfect reflector (ie, the water surface acts as a mirror for acoustic waves), the reflected wave 22c is reflected back towards detector 12 as shown by wave 22d in figure 1. Wave 22d is commonly referred to as a double image (ghost) wave. ) because this wave is due to spurious reflection. Dual images are also recorded by detector 12, but with a reverse polarity and a time delay relative to primary wave 22b. The degenerative effect that the double image (phantasma) achieves has on the seismic bandwidth and resolution is known. In essence, interference between primary and dual-image adventures causes notches, or gaps, in the frequency content recorded by the detectors.

Traces can be used to determine the subsurface (ie ground structure below the surface 24) and to determine the position and presence of reflectors 26. However, dual images cause disturbance in the accuracy of the final subsurface image and For at least this reason, several methods exist for removing double images, i.e. double image removal, from the results of a seismic analysis. In addition, current measurements need to be processed to obtain the corrected position of the various subsurface parts (reflectors). Such a processing method is migration.

U.S. Patent Nos. Nos. 4,353,121 and 4,992,992, the entire contents of which are incorporated herein by reference, describe processing procedures that allow dual images to be removed from seismic data recorded by use of an acquisition device that includes an angled seismic pennant. an angle (in the order of 2 degrees) to the water surface (slanted pennant). Using the tilted pennants it is possible to achieve suppression

dual image mode during add operation (during pre-stacking operations). In fact, the acquired data is redundant, and the processing procedure includes a step of adding or "stacking" to obtain the final image of the subsurface structure from the redundant data. Dual image suppression is performed in the technique during the stacking step because the records contributing to the stack, having been recorded by different receivers, have notches at different frequencies, such that the missing information due to the presence - A notch in one seismic receiver is obtained from another receiver. Additionally, U.S. Patent No. 4,353,121 describes a product

seismic data processing procedures based on the following known steps: (1) common depth point collection, (2) one-dimensional extrapolation (1D) on a horizontal surface, or "data formation", (3) Normal correction MoveOut (NMO), and (4) addition or stack. Data formation is a processing procedure in

which data from N seismic detectors Dn (with positions (xn, zn), where n = 1, N and N is a natural number, Xj = Xj but Zj different from Zj with iej taking values between 1 and Ν) , are used to synthesize data corresponding to seismic detectors that have the same horizontal positions xn and the same constant reference depth Z0 for all seismic detectors.

Data formation is called 1D if it is assumed that seismic waves propagate vertically. In this case, the procedure includes applying to each time domain register acquired by a given seismic detector a delay or a static change corresponding to the vertical propagation time between the true depth zn of a detector Dn and the reference depth z0. In addition, U.S. Patent No. 4,353,121 describes an addition

(primary stacking) by using the NMO correction that aligns the primaries, then adding the double images (double image stacking) by aligning the double image reflections, and then combining the results of these two steps. to obtain a post stacking image with a grouped signal to noise ratio.

Similar to U.S. Patent No. 4,353,121, U.S. Patent No. 4,992,992 proposes to reconstitute seismic data recorded with an inclined cable seismic data as it would have been recorded by a horizontal cable. However, U.S. Patent No. 4,992,992 takes into account the non-vertical propagation of seismic waves by replacing U.S. Patent No. 1D data formation step. 4,353,121 with a 2D data formation step. The 2D data formation step takes into account the fact that wave propagation is not necessarily vertical, unlike what is assumed to be the case in the 1D data formation step proposed by U.S. Patent No. 4,353,121.

More specifically, US 4,992,992 reconstructs two seismic data sets as if they were recorded by a horizontal pennant and then sum the two sets after multiplication by a factor. The first set of data is synthesized assuming that seismic waves are propagating upwards similar to primary waves, and the second set is synthesized assuming that seismic waves are propagating similar to double images. Upward propagation (elevation wave) is defined by horizontal angles of propagation between 0 ° and 180 °, and downward propagation (downward wave) is defined by angles of propagation between 180 ° to 360 ° with the horizontal.

The methods described in U.S. Patent Nos. 4,353,121 and

4,992,992 are seismic processing procedures in one dimension and two dimensions. Such procedures, however, cannot be generalized to three dimensions. This is because a sampling range of sensors in the third dimension is given by the separation between the streamers, in the order of 150 m, which is much larger than the sampling range of sensors along the streamers. which is in the order of 12.5 m. Also, existing procedures may apply a double image removal step at the beginning of processing, which is not always very efficient.

Consequently, it would be desirable to provide systems and

all that avoid the above mentioned problems, for example, provide a 3D seismic processing procedure that allows imaging of subsurface geology based on recorded marine seismic data at different water depths. SUMMARY

According to an exemplary embodiment, there is provided a method for double imaging of seismic data related to a subsurface of a body of water. The method includes admitting data recorded by detectors that are towed by a vessel, the data being associated with waves moving from the subsurface to the detectors; apply a data migration procedure to determine a first image of the subsurface; apply a mirror migration procedure to the data to determine a second image of the subsurface; join the deconvolution of the first image and the second image for double image removal of a subsurface reflectivity; and generating a final subsurface image based on double-image reflectivity of the deconvolution join step. According to yet another exemplary embodiment, there is a processing device for double image capture of seismic data related to a subsurface of a body of water. The processing device includes an interface configured to receive data recorded by detectors being towed by a vessel, the data being associated with waves moving from the subsurface to the detectors; and a processor connected to the interface. The processor is configured to apply a data migration procedure to determine a first subsurface image, apply a mirror migration procedure to the data to determine a second subsurface image, join the deconvolution of the first image and the second image for double imaging of a subsurface reflectivity, and generating a final image of the subsurface based on the double-imaging reflectivity of the deconvolution joining step. According to yet another exemplary embodiment, there is a

computer readable medium including computer-executable instructions, in which the instructions, when executed, implement a method for double imaging of seismic data related to a subsurface of a body of water. The method includes admitting data recorded by detectors that are towed by a vessel, the data being associated with waves moving from the subsurface to the detectors; apply a data migration procedure to determine a first image of the subsurface; apply a mirror migration procedure to the data to determine a second subsurface image; joining the deconvolution of the first image and the second image for double image removal of a subsurface reflectivity; and generating a final subsurface image based on reflectivity with double image removal from the deconvolution junction step. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated into and

constitute a part of the report, illustrate one or more modalities and, together with the description, explain these modalities. In the drawings: Figure 1 is a schematic diagram of a conventional seismic data acquisition system having a horizontal pennant;

Figure 2 is a schematic diagram of a conventional seismic data acquisition system having a slanted pennant;

Figure 3 is a schematic diagram of a procurement system.

seismic data having a curved profile streamer;

Figure 4 illustrates downward and upward moving waves produced by a source and recorded by plural detectors;

Figure 5 is a flow chart of a method for generating a

final image of a subsurface according to an exemplary embodiment;

Figure 6 is a graph illustrating data processed by a migration procedure; Figure 7 is a graph illustrating data processed by a

mirror migration procedure;

Figure 8 is a graph illustrating data processed by a new procedure according to an exemplary embodiment;

Fig. 9 is a flow chart illustrating a method for calculating a final image of a subsurface according to an exemplary embodiment;

Figure 10 is a schematic diagram of a processing apparatus configured to perform a new method according to an exemplary embodiment; and Figure 11 is a flow chart illustrating a method for withdrawing

dual image image according to an exemplary embodiment. DETAILED DESCRIPTION

The following description of exemplary embodiments refers to the accompanying drawings. The same reference numerals in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Rather, the scope of the invention is defined by the appended claims. The following embodiments are discussed for simplicity with respect to migration terminology and structure, mirror migration, and similar mirror migration processes for determining a final image of a subsurface. However, the modalities to be discussed below are not limited to these processes, but may be applied to other processes that are used for seismic data processing or other data related to determining the position of a structure that is not directly reachable for measurements.

Reference throughout the report to "one embodiment" means that a particular feature or structure described in conjunction with one embodiment is included in at least one embodiment of the disclosed object matter. Thus, the appearance of the phrase "in one modality" in various places throughout the report is not necessarily referring to the same modality. Additionally, the particular features and structures may be combined in any suitable manner in one or more embodiments.

According to an exemplary embodiment, there is a method for double image withdrawal migration and mirror image migration by deconvolution junction to generate a final image of a subsurface. In another exemplary embodiment, dual imaging is performed at the end of processing (during an imaging phase) rather than at the beginning as traditional methods. In yet another exemplary embodiment, no data formation step is performed on the data. In yet another exemplary embodiment, the method is applicable without restrictions as for a wave propagation direction. According to yet another exemplary embodiment, a 3D seismic data processing procedure is presented and the 3D procedure allows imaging of the subsurface geology based on marine seismic data recorded at different water depths. According to yet another exemplary embodiment, the data that is processed is collected using streamers having a curved profile, that is, part of the detectors are not pro- vided in a slanted streamer although the detectors have varying depths relative to the surface. from water. These types of pennants were disclosed in French Patent Application filed Serial No. FR1052576 entitled "Method and Device for Acquiring Marine Seismic Data", the entire contents of which are incorporated herein by reference, and also in US Provisional Patent No. 61 / 392,982, Agent Document No. 100001 / 0336-001, entitled "Method and Device for Acquiring Seismic Data", the entire content of which is incorporated herein by reference. Also, French Patent Application filed Ser. No. FR1054599, entitled "Method for Processing Marine Seismic Data" is incorporated herein by reference.

According to another exemplary embodiment, a new dual imaging method is adapted to any wideband acquisition technique. The dual image withdrawal method is noise insensitive, preserving amplitude, and is capable of providing the true dual image destitute earth response (ie the response that would be obtained should the water surface be non-reflective) . Before discussing the details of the method, an examination of the method is believed to be in order. The method produces a conventional migration as well as a mirror migration, and then the method performs a deconvolution join of these two images. A mirror migration is referred to as one that migrates from a duplicate set of receivers that are mirrored above the surface. The process is illustrated in the 2D synthetic data set using a velocity model with a vertical gradient, a small current air gun wave to model pitches, and a variable depth pennant. Modeling of pitches can be done with a reflection of the water surface (double image data). Double-image pitches are processed through deterministic disassignment, migration, mirror migration, and deconvolution join.

In conventional migration, primary events are perfectly stacked, while imperfectly stacked double-image events are present in the form of a small residual causal double-image wave (ie, slowing the primary ones). Conversely, in mirror migration, dual-image events are perfectly stacked with their reversed polarity, while imperfectly stacked primary events are present in the form of a small residual anti-causal wave (ie, primary ones). residuals precede dual well image images).

This dual image of the same reflectivity with two different viewpoints is used to extract true-amplitude dual-image migration. It is a reasonable adoption to consider a small dual image wave as a minimum phase signal, or at least a marginally minimal phase signal. Similarly, mirror migration can be considered to give the same reflectivity as the migration, but distorted by a small wave that is of maximum phase. This can be seen as a binocular view of reflectivity with the conventional color migration image by a normalized minimum phase distortion, and the color mirror migration image by a normalized maximum phase distortion. To recover true-color reflectivity (ie, without distortion) a minimal junction phase, maximum phase decoupling is applied in mirror migration and migration.

Unlike conventional deconvolution, this is a well-posed mathematical problem that means it has a unique solution even when operators have perfect spectral notches. Therefore, there is no requirement for the usual adduction that the reflectivity is white; the reflectivity amplitude spectrum remains arbitrary.

The matching mirror migration technique and double image takeoff junction is well suited for variable depth pennant acquisition. The technique is fully 3D since it does not produce 2D adoptions and has no limitations in cross-line direction, making it suitable for wide azimuth as well as 3D surveys.

The process of gathering marine seismic data was discussed.

in U.S. Provisional Patent Application No. 61 / 392,982, "Method and Device for Acquiring Seismic Data", and thus this process is not repeated here. In addition, the above-identified patent application identifies the possibility of gathering data not only by using traditional streamers, that is, detectors sitting along horizontal lines or along an inclined line, but also using new streamers where part of Detectors can rest on a curved profile (variable depths) or streamers that have multiple slanted sections.

Such a configuration is illustrated in FIG. 3, wherein a streamer 60 has a curved profile defined by three parametric quantities, z0, SO and hc. It is noted that not the full streamer must have the curved profile. In other words, the curved profile should not be constructed forever to apply to the full length of the pennant. While this situation is possible, exemplary modalities do not prohibit having the curved profile applied to only a portion of the pennant. The first parameter Zq indicates the depth of the first detector 54a relative to the water surface 58. This parameter can have a value in the range of meters to tens of meters. For example, Z0 may be around 6 m. However, as would be appreciated by those skilled in the art, the value of Z0 depends on each application and may be related to the depth of the ocean floor, the depth of the reflectors, the sound source energy, etc.

The second parameter So is related to the slope of the

of the streamer 52 relative to a horizontal line 64. The angle s0 is illustrated in Figure 3 and is determined by a tangent T to an initial part of the streamer and the horizontal line 64. It is noted that the inclination of the curved profile at the point 54a is given by a ratio of the change of the curved profile along the Z axis to the change along the X axis. The slope is thus equal to the mathematical value of the tangent of angle s0, ie slope (at the point 54a in figure 3) = tan (s0). In addition, it is noted that for small angles (eg five degrees or less), tan (s) is approximately equal to s0 if the angle is expressed in radians rather than degrees. Thus, for small angles, the slope and angle can be used interchangeably. In one embodiment, the value of S0 may be between 0 and 6 degrees. The example shown in Figure 3 has an initial angle S0 equal to substantially 3 degrees. It is noted that the profile of streamer 52 in Fig. 3 is not scaled as a 3 degree angle is a relatively small amount.

The third parameter hc indicates a horizontal length (distance along the X axis in figure 3 measured from the first detector 54a) of the curved portion of the pennant. This parameter can be in the range of hundreds to thousands of meters. For example, hc is around 3000 m for the configuration shown in figure 3. This parameter defines the end of the curved portion of streamer 52. In other words, streamer 52 may have a first portion 52a having a first profile. curved and a second portion 52b that is either flat or has a different curved profile. The parameter hc defines the first portion 52a. It is noted that in one application streamer 52 has both first portion 52a and second portion 52b, while in another application streamer 52 has only first portion 52a. In other words, in some embodiments, the pennant does not extend along the total curved profile, that is, a pennant length projected on the X axis is less than hc.

According to another exemplary embodiment, the curved profile of streamer 60 can be described approximately by the following equations:

(1) z (h) = z0 + s0h

r (U

1-0.5

v V1CJJ

for h <hc, and

(2) z (h) = z0 + SO-0.5 · hc for h> hc.

In these equations, ζ is measured along the Z axis and h is measured along the X axis, where Z is perpendicular to the water surface and X extends along the water surface. Also, it is noted that only equation (1) may be sufficient to define the shape of the pennant, depending on the length of the pennant. In other words, in some embodiments, the pennant does not have to have the flat portion. For these specific equations, it has been found that the clarity of the subsurface images improves substantially. Those skilled in the art would understand that the values provided by equations (1) and (2) are approximated as detectors 70 are under constant motion exerted by various streams of water and vessel motion. In other words, it is understood that detectors that are provided substantially on the curved profile described by equation (1) and / or (2), for example, at positions closest to 10 to 20% for the actual curve in terms of the current depth. z (h) are considered to be covered by the above equations. The same is true for 72 birds that are configured to maintain a curved profile. The curved profile can be one of a parable, a circle, a hyperbole or a combination of these shapes.

Although the curved profile pennant discussed above provides better results than existing pennant profiles, the processing discussed in the following exemplary embodiments applies equally to traditional (e.g. horizontal, inclined) pennant profiles.

Before discussing the new process of dual imaging, the provision of a few definitions and concepts related to seismic data processing is believed to be in order. For this purpose, Figure 4 illustrates an acquisition composition to be used as an example. As discussed later, another composition may be used.

Fig. 4 illustrates a vessel 84 having an acoustic source 86 and pulling a streamer 88. Streamer 88 includes plural detectors 90 and detectors are distributed, in this exemplary embodiment, into an inclined streamer. The incident waves 80 reach the bottom 92 of the ocean, where part of them is reflected. However, part of the incident waves continues to travel on the subsurface (bottom structure 92) where it is reflected by various reflectors 94. At this point, a reflected wave 82 begins to propagate toward the water surface 96. This upwardly shifting reflected wave 82 is recorded by detectors 90. However, the reflected wave 82 further shifts to surface 96, where it is reflected by the water surface, thereby forming double images 98, which also are detected by detectors 90. The incident wave 80 (ie the wave emitted by source 86) is as follows.

It is assumed to be downward displacement and described by a mathematical function D. This incident wave D (x, y, z, t) depends on the position (x, y, z) and time t at any point in space. The incident wave D (x, y, z, t) is recursively synthesized depth ζ during the migration process. The downward wave is being initialized to a depth of seismic source zs. Since there are η detectors, with η from 1 to N, where N is a natural number, the incident wave D at full depth ηΔζ is then recursively calculated by calculating the incident wave D (x, y, ζ + Δζ , t) at a depth ζ + Δζ from the incident wave D (x, y, z, t) the depth z. This is done until all pennant detectors are taken into account. Similarly, the reflected wave 82, which is described by a function

math U (x, y, z, t) is assumed to be moving up and is initialized to a depth ζ = zr, where zr is a depth of the detectors if all detectors have the same depth. If the detectors are distributed on a slanted pennant or on a pennant having a curved profile, the U function needs to be adjusted for each detector as discussed later. The reflected wave U in total volume is then recursively calculated by calculating the upward-moving wave U (x, y, ζ + Δζ, t) at a depth ζ + Δζ from the upward-moving wave U (x, y, z, t) at a depth z. The depths of the detectors, that is, the fact that the source and the

Detectors can have non-relative depths relative to each other and can be accounted for by adding sources and detectors to a corresponding ζ through all recursive calculations. For example, a detector provided at a depth zr, sitting between ηΔζ and (η + 1) Δζ is added during the recursive calculation of ΙΙ ((η + 1) Δζ) of ΙΙ (ηΔζ).

In the case of a mirror migration, the water surface is used as a mirror: instead of "looking" towards the sea floor, one "looks" towards the water surface to see the reflectors located below the seismic receptors. Mirror migration is described in French patent application no. 1050278, entitled "Method for Processing Marine Seismic Data", and U.S. Provisional Patent Application No. 61 / 393,008, Agent Document no. 100002 / 0336-002, entitled "Method and Device for Processing Seismic Data", the entire contents of which are incorporated herein by reference. The same requests also describe an equivalent mirror migration.

Once migration is performed, a d (x, y, z) image is obtained that includes residual double image waves. If the image is obtained by using the equivalent mirror migration method, the residual double images are symmetrical. The image d (x, y, z) can be considered to be equal to the convolution reflectivity r (x, y, z) with residual with a residual double image transfer function g (z) as expressed by the following equation. :

d (x, y, z) = g (z) r (x, y, z). Since the residual dual image transfer function g (z) depends only weakly on one position (x, y, z), the above ratio is valid within a given volume. The reflectivity estimation operation r (x, y, z) from the

data d (x, y, z) is called deconvolution. This operation requires an estimate of the transfer function g (z). Two processes are known to those skilled in the art for estimating the transfer function g (z) and calculating reflectivity r (x, y, z) from data d (x, y, z). One process is reflectivity zero phase deconvolution

white. This process assumes that g (z) is symmetrical in ζ and that reflectivity has a white autocorrelation in ζ (equal to an impulse in z = 0). A Fourier transform G (kz) of g (z) is real, and a Fourier transform R (x, y, kz) of r (x, y, z) is complex with modulus 1. Hence, it can be derived that G (kz) is the modulus of D (x, y, kz), the Fourier transform in ζ of d (x,

y, z).

The other process is the minimal phase deconvolution with white reflectivity. This process assumes that g (z) is a minimal phase and that reflectivity has a white autocorrelation at z. Zero phase deconvolution makes deconvolution possible

mirror migration (because in this case g (z) is symmetrical) and the minimal phase deconvolution allows the deconvolution of the standard migration because for the migration process the residual double image transfer function is causal and can considered to be of minimum phase. Regardless of which of the two procedures is used to obtain reflectivity (migration followed by minimal phase deconvolution or equivalent mirror migration followed by zero phase deconvolution), the adoption of white reflectivity is necessary for traditional processes. This adoption was commonly used in seismic processing, but used less and less because so-called preserved amplitude processing is becoming more and more the default. In this type of processing, it is not only the position of the reflectors that is of interest, but also their amplitude, and in this context the adoption of white reflectivity cannot be used.

According to an exemplary embodiment illustrated in FIG. 5, a new processing method does not require the adoption of white reflectivity and preserves amplitude. In step 500, the acquired data, for example with the composition shown in figure 4, is admitted to a processing apparatus. In step 502, the migration process is applied to the data allowed for generation in step 504 of a di image. Similarly, the same data from step 500 can be processed with a mirror migration procedure in step 506 to generate in step 508 an image d2. In one application, no double image withdrawal is applied to the admitted data from step 500 before the steps. 504 and 508. Image di (x, y, z) is obtained by migration (where a record of each receiver is inserted in its true position (xr, yr, zr)) and image d2 (x, y, z) is obtained by mirror migration (where a record of each receiver is inserted with a change of signal only in the mirror position of the receiver (xr, yr, -zr)).

Migration aligns the primary events so that a coherent sum of the primary events is possible and is shown in figure 6. The migration produces the double image events to correspond to positions posições (on the Z axis in figure 4) greater than the corresponding primary events. This is illustrated in Figure 6 by the white areas 600 following each line 602. Therefore, the image di (x, y, z) includes residual double image waves that are represented by a causal minimal phase transfer function gmin (z), which is contaminated by the convolution of reflectivity r (x, y, z) as shown in equation (3):

di (x, y, z) = gmin (z) r (x, y, z). (3) The minimum phase transfer function gmin (z) is a function

causal and its inverse is also causal.

Mirror migration aligns dual-image events by changing their signal to make their polarity match that of the primary events. Thus, a coherent sum of the double image events is possible and is shown in figure 7. The primary events in this case correspond, as shown in figure 7, to positions ζ smaller than the corresponding double image events. Figure 7 shows the white areas 600 being distributed above (on the Z axis) on lines 602. Image d2 (x, y, z) includes residual double image waves that are represented by a gmax maximal anticausal phase transfer function ( z), which is contaminated by the convolution of reflectivity r (x, y, z), as shown in equation (4):

d2 (x, y, z) = gmax (z) * r (x, y, z) (4)

The maximum phase transfer function is an anti-causal function and its inverse is also anticausal.

In other words, migration coherently stacks the primary events, double-image events being imperfectly stacked such that migration has a small residual double-image wave that is causal. Mirror migration coherently stacks dual image events with their reversed polarity, such that mirror migration has a small residual double image wave that is anticausal. In one exemplary embodiment, the dual image withdrawal method illustrated in Figure 5 uses a "binocular view" of two images (di and d2) of the same reflectivity r with a different point of view to extract a withdrawal migration. true-amplitude dual-image image that would have been obtained by conventional migration if the water surface had not been reflective. After calculating di (x, y, z) and d2 (x, y, z) by mirror migration and migration in steps 504 and 508, respectively, the reflectivity r (x, y, z) can be obtained by a "deconvolution join" procedure performed in step 510 (see figure 5). The deconvolution junction refers to a calculation procedure allowing the reflectivity r (x, y, z), a causal operator gmm (z), and an anticausal operator gmax (z) to be obtained from the images di (x, y, z) and d2 (x, y, z) such that equations (3) and (4) are exactly or approximately satisfied within a certain computational volume V. More specifically , the causal operator gmin (z) is a minimum phase operator, and the anticausal operator gmax (z) is a maximum phase operator. A minimum phase operator or a maximum phase operator is known in control theory. For example, the phase operator has the property that it is causal and stable and its inverse is causal and stable. The maximum phase operator is causal and stable and its inverse is causal and unstable. After the deconvolution join step 510, a final image "d" of the subsurface is generated in step 512. The final image d is illustrated in figure 8 and it can be seen that the white areas 600 are greatly reduced relative to the figures. 6 and 7 using the conventional approach.

According to an exemplary embodiment illustrated in Fig. 9, a deconvolution join procedure includes a step 900 of defining a volume V = [xmin, xmax] x [ymin, ymax] X [zmin, zmax] and one step 902 of defining a length Dz that depends on a maximum separation between an event and its double image. Additionally, the procedure includes a step 904 of calculating gmm (z), gmax (z), and r (x, y, z) by consideration that r is being defined in volume V, gmin (z) in the interval [ 0, Dz] with a normalization gmin (z = 0) = 1, gmax (z) in the range [-Dz, 0] with a normalization gmax (z = 0) = 1. Calculation step 904 is reached by the mini- a cost function C defined by:

C = Z (x, y, z) ε ν {[di (x, y, z) - gmin (z) * r (x, y, z)] 2 + [d2 (x, y, z) - gmax (z) * r (x, y, z)] 2}.

The reflectivity r (x, y, z) is being calculated on a total volume of interest by juxtaposing r (x, y, z) calculated on volume V with an overlap zone. It is also possible to use the characteristics of the minimum phase of gmin (z) and the maximum phase of gmax (z). Based on the calculated r, a final image is generated at step 906.

Another exemplary embodiment includes substitution of the functions gmín (z) and gmáx (z) which depend only on "z" with three dimensional functions gmín (x, y, z) and gmax (x, y, z) which are causal in ζ and anticausal in z, respectively. In addition, the convolution of a dimension in ζ can be replaced by a three-dimensional convolution. This mode makes it possible to take into account the dependence of residual double images on the propagation wave angles.

In yet another exemplary embodiment, which also makes it possible to take into account the dependence of residual double images on propagation angles, a transform called a (τ, px, py), transform is applied to di (x, y, z) and d2 (x, y, z), which transforms the di (x, y, z) data into Di (px, py, τ) and the d2 (x, y, z) data into D2 (px, py, τ). ). A definition of the transform (τ, ρ *, py), also called "inclined wedge" can be found, for example, in Seismic Data Processing, Ozdogan Yilmaz, Society of Exploration Geophysicists 1987, Chapter 7, page 429, or in US Patent No. 6,574,567, the total contents of which are incorporated herein by reference.

Then, for all values (px, py), the residual double images Gmin (px, py) (T) and Gmax (px, py) (T) are calculated assuming to be causal and anticausal respectively in τ, phase. minimum and maximum in τ, and a reflectivity R (px, py, τ) such that: C (px, py) = Σ {[Di (px> py, τ) - Gmin (px, py) (T) * R (px, py, τ)] 2 + [D2 (px,

py> τ) - Gmax (px, py) (T) * R (px, py, τ)] 2}

is a minimum for all (px, py), the operation "*" being in this case a convolution in τ. The double-image image, ie the reflectivity r (x, y, z), is obtained by calculating the inverse of R (px, py, τ) with the transformation (τ, px, py).

In the above description, the migrations used are depth migrations for the di (x, y, z) and d2 (x, y, ζ) images. The deconvolution join procedure can also be used with images resulting from time migrations. In the case of a time migration, the image d (x, y, τ) has a temporal parameter τ overriding the depth parameter z. For time migration, a velocity model vi (x, y, τ) is used to perform the coherent sum of primary events. The equivalent of mirror time migration processing is a migration where, after changing the polarity of the input data, a velocity v2 (x, y, τ) is used to achieve a coherent sum of double image events. Then a deconvolution junction can be applied to calculate the final image of the subsurface and the deconvolution junction is described by:

di (x, y, τ) = gmin (T) * r (x, y, τ) and d2 (x, y, τ) = gmax (T) * r (x, y, τ). The deconvolution join step can be generalized to deconvolve more than two data sets, particularly in the case where the receivers are of different types. For example, if pressure-sensitive receptors such as hydrophone and geophone receptors are used together on the same or different pennants, a more complex deconvolution is required to obtain the final image. For example, it is assumed that the migration result is di (x, y, z) and the mirror migration result is d2 (x, y, z) for hydrophone receivers and the migration result is d3 ( x, y, z) and the result of mirror migration is d4 (x, y, z) for geophones. Mirror migration of geophone data is achieved by inserting the records of each receiver (geophone) at their mirror positions (xr, yr, -zr), but without changing the signal to a vertical geophone with a signal changed to a horizontal geophone receiver.

The deconvolution junction with four admissions is obtained by modeling the migrations and mirror migrations with the following equations:

di (x, y, z) = ghmin (z) * r (x, y, z); d2 (x, y, z) = ghmax (z) * r (x, y, z);

d3 (x, y, z) = ggmin (z) * c (z) * r (x, y, z); and d4 (x, y, z) = g9max (z) * c (z) * r (x, y, z). Then, by using the squared minimum cost function, the causal and minimum phase operators ghmin (z) and g9min (z), the anticausal and maximum phase operators ghmax (z) and g9max (z) , the calibration operator c (z) as well as the reflectivity r (x, y, z) can be determined from the migrations and mirror migration images di (x, y, z), d2 (x, y, z), d3 (x, y, z) and d4 (x, y, z).

The cost function can be weighed to take into account the different noise spectrum of hydrophone sensors and geophone sensors. For example, in time migration, the cost function to be minimized is written to domain f, the Fourier transform of τ:

C = I {[di (x, y, f) - ghmin (f) r (x, y, f) f / Bh (f) + [d2 (x, y, f) - ghmax (f) • r ( x, y, f) f / Bh (f »·

{[d3 (x, y, f) - g9min (f) c (f) r (x, y, f)] 2 / Bg (f) + [d4 (x, y, f) - g9max (f) • c (f) · r (x, y, f)] 2 / B9 (f)}, where Bh (f) and B9 (f) are estimates of the noise energy spectrum.

hydrophone and geophone, respectively.

The procedures described above are not limited to processing data acquired using linear streamers with a constant slope as shown in Figure 1. The above procedures are also applicable to data acquired using streamers each having various sections with different inclinations, or streamers having one or more inclined sections and one or more horizontal sections, or horizontal streamers located at different depths or streamers having a curved profile.

The above discussed procedures and methods can be im-

The hardware, firmware, software, or a combination of these can be used to perform the various steps and operations described herein. The processing apparatus 1000 of FIG. 10 is an exemplary computing structure that may be used in conjunction with such a system.

Exemplary processing apparatus 1000 suitable for performing the activities described in the exemplary embodiments may include a server 1001. Such a server 1001 may include a central processor (CPU) 1002 coupled to a random access memory (RAM) 1004 and a memory of only read (ROM) 1006. ROM 1006 may also be other types of storage media for storing programs, such as programmable ROM (PROM) 1 erasable PROM (EPROM), etc. Processor 1002 can communicate with other internal and external components via inlet / discharge (I / O) circuitry 1008 and pickup bars 1010 to provide control signals and the like. The 1002 processor performs a variety of functions as is known in the art, as represented by the software and / or firmware instructions.

Server 1001 may also include one or more data storage devices, including 1012 hard drives and hard drives, 1014 CD-ROM drives, and other hardware capable of reading and / or storing information such as DVD, etc. . In one embodiment, the software for performing the above steps may be stored and distributed on a CD-ROM 1016, floppy disk 1018, or other form of media capable of portable storage of information. This storage medium can be inserted into and read by devices such as CD-ROM drive 1014, floppy drive 1012, etc. Server 1001 may be coupled to a 1020 display, which may be any known display type or display screen, such as LCD displays, plasma displays, cathode ray tubes (CRT), etc. A 1022 user input interface is provided, including one or more user interface mechanisms such as a mouse, keyboard, microphone, touch pad, touch screen, speech recognition system, etc.

Server 1001 can be attached to other devices such as sources, detectors, etc. The server may be part of a larger network configuration such as a global area network (GAN) such as the Internet 1028, which allows last connection to various land lines and / or mobile computing devices.

According to an exemplary embodiment illustrated in Fig. 11, there is a method for double image capture of seismic data related to a subsurface of a body of water. The method includes a step 1100 of admitting data recorded by detectors that are towed by a vessel, the data being associated with waves moving from the subsurface to the detectors; a step 1102 of applying a data migration procedure to determine a first image of the subsurface; a step 1104 of applying a mirror migration procedure to the data to determine a second subsurface image; a step 1106 of deconvolving junction of the first image and the second image for double image removal of the subsurface reflectivity; and a step 1108 of generating a final image of the subsurface based sub-reflectivity with the deconvolution junction step.

Exemplary embodiments disclosed provide an apparatus and method for seismic data processing. It should be understood that this description is not intended to limit the invention. Rather, 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. Additionally, in the detailed description of exemplary embodiments, numerous specific details are placed 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.

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

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice it, including producing and using any devices or systems, and performing any embodied 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.

Claims (15)

1. Method for taking double images of seismic data relating to a subsurface of a body of water, the method comprising: admitting (1100) data recorded by detectors that are towed by a vessel, the data being associated with waves moving from the subsurface to the detectors; apply (1102) a data migration procedure to determine a first image (d1) of the subsurface; apply (1104) a mirror migration procedure to the data to determine a second subsurface image (d2); adding (1106) the deconvolution of the first image (d1) and the second image (d2) for double image removal of a subsurface reflectivity; and generating (1108) in a processor a final image (d) of the subsurface based reflectivity with double image removal of the deconvolution join step. A method according to claim 1, wherein the double image removal is performed during an image phase and not in a preprocessing phase. A method according to claim 1, wherein no data formation step is performed on the data. A method according to claim 1, wherein an angle of displacement of waves propagating from the subsurface to the detectors or from a water surface to the detectors is not restricted. A method according to claim 1, wherein the data is collected from streamers having a curved profile. A method according to claim 1, wherein the deconvolution junction comprises: determining reflectivity r (x, y, z), a minimal phase transfer function gmin (z), and a phase transfer function maximum gmax (z) based on the equations: di (x, y, z) = gmin (z) T (x, y, z), and d2 (x, y, z) = gmax (z) * r (x, y, z), where ζ is a depth of a point relative to the water surface, and χ and y are coordinates of the point in a phase substantially parallel to the water surface. A method according to claim 1, wherein the deconvolution junction comprises: calculating a cost function C for determining reflectivity, wherein the cost function C is given by: C = Σ (χ, ν , ζ) and ν {[di (x, y, z) - gmin (z) * r (x, y, z)] 2 + [d2 (x, y, z) - gmax (z) * r (x , y, z)] 2}, where di (x, y, z) is the first image, d2 (x, y, z) is the second image, gmin (z) is a minimum phase transfer function , gmax (z) is a maximum phase transfer function, ζ is a depth of a point relative to the water surface, χ and y are coordinates of the point in a plane substantially parallel to the water surface, and V is a pre volume. - determined. A method according to claim 1 further comprising: applying a transformation (τ, px, py) to di (x, y, z) and d2 (x, y, z) to transform the first image di (x, y, z) at D1 (px, py, τ) and the d2 (x, y, z) data at D2 (px, py, τ). A method according to claim 1, wherein the data includes hydrophones and geophones records. A method according to claim 9, wherein one result of the migration procedure is di (x, y, z) and a result of the mirror migration procedure is d2 (x, y, z). for hydrophone receivers and one result from the migration procedure is d3 (x, y, z) and one result from the mirror migration procedure is d4 (x, y, z) for geophones. A method according to claim 10, further comprising: generating the final image using a deconvolution junction of d x x y, z), d 2 (x, y, z), d 3 (x, y, z), and d4 (x, y, z) and based on the following equations: di (x, y, z) = ghm (n (z) * r (x, y, z); d2 (x, y, z) = ghmax (z) * r (x, y, z); d3 (x, y, z) = g9min (z) * c (z) * r (x, y, z); and d4 (x, y, z) = g9max (z) * c (z) * r (x, y, z), where ghm [n and g9m [n are minimum phase transfer functions, ghmax (z) and g9max (z) are transfer functions maximum phase, ζ is a depth of a point relative to the water surface, χ and y are coordinate of the point in a plane substantially parallel to the water surface, and c (z) is a calibration operator. 12. A processing device (1000) for dual image withdrawal of seismic data related to a subsurface of a body of water, the processing device (1000) comprising: an interface (1010) configured to receive data. recorded by detectors being towed by a vessel, the data being associated with waves moving from the subsurface to the detectors; and a processor (1002) connected to the interface (1010) and configured to apply a data migration procedure to determine a first subsurface image, apply a mirror migration procedure to the data to determine a second image of the subsurface, join the deconvolution of the first image and the second image for dual imaging of a subsurface reflectivity, and generate a final subsurface image based on the withdrawal reflectivity. double image of the deconvolution join step. A processing device according to claim 12, wherein the processor is configured to: determine the reflectivity r (x, y, z), a minimum phase transfer function gmin (z), and a function maximum phase transfer values gmax (z) based on the equations: di (x, y, z) = gmin (z) r (x, y, z), and d2 (x, y, z) = gmax (z) * r (x, y, z), where ζ is a depth of a point relative to the water surface, and χ and y are coordinates of the point in a plane substantially parallel to the water surface. A processing device according to claim 12, wherein a result of the migration procedure is di (x, y, z) and a result of the mirror migration procedure is d2 (x, y, z). for hydrophone receivers and one result from the migration procedure is ds (x, y, z) and one result from the mirror migration procedure is d4 (x, y, z) for geophones. A processing device according to claim 14, wherein the processor is further configured to: generate the final image using a deconvolution junction of di (x, y, z), d2 (x, y, z ), d3 (x, y, z), and d4 (x, y, z) and based on the following equations: di (x, y, z) = ghmin (z) * r (x, y, z) ; d2 (x, y, z) = ghmax (z) * r (x, y, z); d3 (x, y, z) = g9min (z) * c (z) * r (x, y, z); and d4 (x, y, z) = g9max (z) * c (z) * r (x, y, z), where ghmin and ggmin are minimum phase transfer functions, ghmax (z) and g9max (z) are maximum phase transfer functions, ζ is a depth of a point relative to the water surface, χ and y are coordinate of the point in a plane substantially parallel to the water surface, and c (z) is a calibration operator.