阅读说明：本技术 一种基于照明方向约束的被动源干涉偏移成像方法和系统 (Passive source interference offset imaging method and system based on illumination direction constraint ) 是由 王德利 苏一哲 胡斌 于 2021-09-26 设计创作，主要内容包括：本申请公开了一种基于照明方向约束的被动源干涉偏移成像方法和系统,本方法包括对单点脉冲型被动源地震记录进行干涉处理,得到被动源的反褶积函数；对反褶积函数进行倾斜叠加处理,得到有效照明信息方向；基于反褶积函数和有效照明信息方向,得到偏移成像结果。本系统包括反褶积模块、照明分析模块和成像模块；反褶积模块用于对单点脉冲型被动源的地震记录进行干涉处理,得到反褶积函数；照明分析模块用于对反褶积函数进行倾斜叠加处理,得到有效照明信息方向；成像模块根据反褶积函数和有效照明信息方向,得到偏移成像结果。本申请在不满足传统假设的情况下,可以提取数据中包含的有效信息,获得准确的成像结果。(The application discloses a passive source interference migration imaging method and system based on illumination direction constraint, and the method comprises the steps of carrying out interference processing on single-point pulse type passive source seismic records to obtain a deconvolution function of a passive source; performing oblique superposition processing on the deconvolution function to obtain an effective illumination information direction; based on the deconvolution function and the effective illumination information direction, an offset imaging result is obtained. The system comprises a deconvolution module, an illumination analysis module and an imaging module; the deconvolution module is used for carrying out interference processing on the seismic record of the single-point pulse type passive source to obtain a deconvolution function; the illumination analysis module is used for carrying out oblique superposition processing on the deconvolution function to obtain an effective illumination information direction; and the imaging module obtains an offset imaging result according to the deconvolution function and the effective illumination information direction. According to the method and the device, under the condition that the traditional hypothesis is not met, effective information contained in the data can be extracted, and an accurate imaging result is obtained.)

1. A passive source interference offset imaging method based on illumination direction constraint is characterized by comprising the following steps:

carrying out interference processing on the seismic record of the single-point pulse type passive source to obtain a deconvolution function of the passive source, wherein the deconvolution function is used for obtaining a virtual shot gather record;

performing oblique superposition processing on the deconvolution function, and extracting ray parameters corresponding to peak values at zero time to obtain effective illumination information directions;

and performing offset imaging processing on the virtual shot gather record based on the deconvolution function and the effective illumination information direction to obtain an offset imaging result and finish passive source interference offset imaging.

2. The illumination direction constraint-based passive source interference offset imaging method according to claim 1, wherein the method for obtaining the deconvolution function comprises:

under the condition of pulse type passive source single-point distribution, performing cross correlation on seismic records of a first detector and a second detector, and reconstructing a Green function between the first detector and the second detector, wherein the Green function is a cross correlation function, and the first detector is a virtual seismic source;

carrying out autocorrelation on the seismic record of the first detector to obtain an autocorrelation function of the first detector;

and obtaining the deconvolution function of the passive source based on the cross-correlation function and the autocorrelation function.

3. The illumination direction constraint-based passive source interference offset imaging method according to claim 2, wherein the method for obtaining the effective illumination information direction comprises:

establishing a radon model and a least square tilt superposition function, and solving a least square solution of the radon model;

establishing an iterative threshold contraction function for iteration in a time domain based on a least square solution of the radon model;

based on the iteration threshold contraction function, performing high-resolution linear oblique superposition processing on the deconvolution function to obtain ray parameter distribution of the deconvolution function at a zero moment;

and obtaining the effective illumination information direction based on the ray parameter distribution.

4. The illumination direction constraint-based passive source interference offset imaging method according to claim 3, wherein the method for obtaining the offset imaging result comprises:

taking the effective illumination information direction as a constraint, and carrying out Gaussian beam offset processing on the deconvolution function to generate local offset imaging recorded by the virtual shot gather;

and performing superposition processing on the local offset imaging to obtain an offset imaging result.

5. The illumination direction constraint-based passive source interference shift imaging method according to claim 4, wherein the method for obtaining the local shift imaging comprises:

and obtaining the local migration imaging based on the forward wave field function and the backward wave field function.

6. The illumination direction constraint-based passive source interference shift imaging method according to claim 5, wherein the method for obtaining the forward wave field function comprises:

converting the deconvolution function from ray parameters into angle coordinates, expressing the angle coordinates by Gaussian beams along different directions, and obtaining illumination direction constraint according to the ray angle of the effective illumination information direction;

and obtaining the forward wave field function based on the ray parameter distribution of the deconvolution function and the illumination direction constraint.

7. The illumination direction constraint-based passive source interference shift imaging method according to claim 5, wherein the method for obtaining the back propagation wave field function comprises:

adjusting the kirchhoff integral to the detector boundary of the deconvolution function, and constructing a progressive form of the deconvolution function based on Gaussian beam approximation;

and superposing the Gaussian beams in all directions based on the progressive form to obtain the back propagation wave field function.

8. A passive source interference offset imaging system based on illumination direction constraint is characterized by comprising a deconvolution module, an illumination analysis module and an imaging module;

the deconvolution module is used for carrying out interference processing on the seismic record of the single-point pulse type passive source to obtain a deconvolution function, and the deconvolution function is used for obtaining a virtual shot gather record;

the illumination analysis module is used for performing oblique superposition processing on the deconvolution function and extracting ray parameters corresponding to peak values at zero time to obtain an effective illumination information direction;

and the imaging module is used for carrying out offset imaging processing on the virtual shot gather record according to the deconvolution function and the effective illumination information direction to obtain an offset imaging result.

9. The illumination direction constraint based passive source interference shift imaging system according to claim 8, wherein the imaging module comprises a forward wave field unit, a backward wave field unit and a shift imaging unit;

the forward wave field unit is used for obtaining a forward wave field according to the deconvolution function and the effective illumination information direction;

the back propagation wave field unit is used for constructing a Gaussian beam function based on the deconvolution function and overlapping the Gaussian beam function to obtain a back propagation wave field;

and the offset imaging unit is used for obtaining an offset imaging result according to the forward transmission wave field and the backward transmission wave field.

Technical Field

The application belongs to the technical field of passive source seismic exploration imaging, and particularly relates to a passive source interference migration imaging method and system based on illumination direction constraint.

Background

In seismic exploration, natural earthquakes, background noises and the like are generally considered to be interferences, and the noises also conform to the propagation rule of seismic waves and carry abundant underground medium information. Passive source interferometric imaging methods are methods of imaging using these so-called "noise". The method does not need to know the prior information of the underground medium, is completely data-driven, and can eliminate the influence of shallow complex medium due to data reconstruction. The passive source seismic exploration is also more suitable for areas where the active source seismic exploration is not convenient to implement, such as cities, mountainous areas with complex terrain and the like.

The seismic interference can be realized by performing cross correlation on seismic responses received by different detectors to reconstruct a reflection response which is generated when one of the detectors is used as a virtual seismic source for excitation and the other detectors are used for receiving. Conventional passive source interferometric imaging methods are based on the assumption that the seismic sources in the subsurface are sufficiently randomly distributed to illuminate the receivers from all possible angles. In actual exploration situations, the distribution of subsurface sources often fails to meet this assumption. This can lead to inaccuracies in the imaging results or contain a large number of interference artifacts therein.

Disclosure of Invention

The application provides a passive source interference offset imaging method and system based on illumination direction constraint.

In order to achieve the above purpose, the present application provides the following solutions:

a passive source interference offset imaging method based on illumination direction constraint comprises the following steps:

carrying out interference processing on the seismic record of the single-point pulse type passive source to obtain a deconvolution function of the passive source, wherein the deconvolution function is used for obtaining a virtual shot gather record;

performing oblique superposition processing on the deconvolution function, and extracting ray parameters corresponding to peak values at zero time to obtain effective illumination information directions;

and performing offset imaging processing on the virtual shot gather record based on the deconvolution function and the effective illumination information direction to obtain an offset imaging result and finish passive source interference offset imaging.

Preferably, the method for obtaining the deconvolution function includes:

under the condition of pulse type passive source single-point distribution, performing cross correlation on seismic records of a first detector and a second detector, and reconstructing a Green function between the first detector and the second detector, wherein the Green function is a cross correlation function, and the first detector is a virtual seismic source;

carrying out autocorrelation on the seismic record of the first detector to obtain an autocorrelation function of the first detector;

and obtaining the deconvolution function of the passive source based on the cross-correlation function and the autocorrelation function.

Preferably, the method for obtaining the effective illumination information direction includes:

establishing a radon model and a least square tilt superposition function, and solving a least square solution of the radon model;

establishing an iterative threshold contraction function for iteration in a time domain based on a least square solution of the radon model;

based on the iteration threshold contraction function, performing high-resolution linear oblique superposition processing on the deconvolution function to obtain ray parameter distribution of the deconvolution function at a zero moment;

and obtaining the effective illumination information direction based on the ray parameter distribution.

Preferably, the method for obtaining the offset imaging result comprises:

taking the effective illumination information direction as a constraint, and carrying out Gaussian beam offset processing on the deconvolution function to generate local offset imaging recorded by the virtual shot gather;

and performing superposition processing on the local offset imaging to obtain an offset imaging result.

Preferably, the method of obtaining the local offset image includes:

and obtaining the local migration imaging based on the forward wave field function and the backward wave field function.

Preferably, the method for obtaining the forward wavefield function includes:

converting the deconvolution function from ray parameters into angle coordinates, expressing the angle coordinates by Gaussian beams along different directions, and obtaining illumination direction constraint according to the ray angle of the effective illumination information direction;

and obtaining the forward wave field function based on the ray parameter distribution of the deconvolution function and the illumination direction constraint.

Preferably, the method for obtaining the anti-wave field function comprises:

adjusting the kirchhoff integral to the detector boundary of the deconvolution function, and constructing a progressive form of the deconvolution function based on Gaussian beam approximation;

and superposing the Gaussian beams in all directions based on the progressive form to obtain the back propagation wave field function.

The application also discloses a passive source interference offset imaging system based on illumination direction constraint, which comprises a deconvolution module, an illumination analysis module and an imaging module;

the deconvolution module is used for carrying out interference processing on the seismic record of the single-point pulse type passive source to obtain a deconvolution function, and the deconvolution function is used for obtaining a virtual shot gather record;

the illumination analysis module is used for performing oblique superposition processing on the deconvolution function and extracting ray parameters corresponding to peak values at zero time to obtain an effective illumination information direction;

and the imaging module is used for carrying out offset imaging processing on the virtual shot gather record according to the deconvolution function and the effective illumination information direction to obtain an offset imaging result.

Preferably, the imaging module comprises a forward wave field unit, a backward wave field unit and an offset imaging unit;

the forward wave field unit is used for obtaining a forward wave field according to the deconvolution function and the effective illumination information direction;

the back propagation wave field unit is used for constructing a Gaussian beam function based on the deconvolution function and overlapping the Gaussian beam function to obtain a back propagation wave field;

and the offset imaging unit is used for obtaining an offset imaging result according to the forward transmission wave field and the backward transmission wave field.

The beneficial effect of this application does:

the application discloses a passive source interference migration imaging method and system based on illumination direction constraint, which can be used for seismic exploration in areas unsuitable for active source exploration, such as surrounding areas of cities and environmental protection areas, and have a wide application range; the method does not need manual seismic source excitation, and only needs to arrange the seismograph station in the exploration area for data receiving, thereby saving the cost and protecting the environment; in the actual situation that the basic assumption of the traditional method is not met, effective information contained in the data can be extracted, and an accurate imaging result is obtained.

Drawings

In order to more clearly illustrate the technical solution of the present application, the drawings needed to be used in the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without inventive exercise.

Fig. 1 is a schematic flowchart of a passive source interference offset imaging method based on illumination direction constraint according to a first embodiment of the present application;

FIG. 2 is a diagram illustrating reconstruction of a reflection response between two detectors according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a passive source interference shift imaging system based on illumination direction constraint according to a second embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.

Example one

As shown in fig. 1, a schematic flowchart of a passive source interference offset imaging method based on illumination direction constraint in an embodiment of the present application is provided, which mainly includes three steps of passive source interference, illumination information extraction, and illumination direction constraint offset imaging. The three steps of the first embodiment of the present application are described in detail below.

Firstly, interference processing is carried out on the seismic record of the single-point pulse type passive source to obtain a deconvolution function of the passive source, and inaccurate interference virtual shot gather record can be obtained through the deconvolution function.

For impulse type passive sources, Wapenaar&Fokkema (2006) describes continuous uniform distribution in an acoustic medium at a passive source (each located at x)_sHere, in the first embodiment, the symbol x_sCharacterizing the passive source), two detectors x are reconstructed_A、x_B(wherein, x_ACharacterizing virtual sources) of seismic dataThe relational expression (c) of (c). According to the method, when two detectors are positioned on the free surface to record passive source earthquake, the Green function between the two detectors is reconstructedI.e. the reflection response of the subsurface interface:

wherein R represents a real part, { }^*Representing the complex conjugate, ω is the angular frequency, and ^ represents the wavefield in the frequency domain, ρ and c_pRepresenting the density and sound wave velocity at passive source locations in the medium.

In equation 1, the wavefield is observedFrom at x_sThe vertical particle velocity Green function generated by the stress of the vertical pointFourier transform with seismic source functionThe product of (a) represents. The right hand side of equation 1 corresponds to the cross-correlation in the time domain. By making pairs at x_sIntegrating the passive sources of (a) represents a superposition of the passive sources distributed in the subsurface medium. Integration results from the expected reflected response(shown in virtual source x_BIs excited at x_AThe received vertical particle velocity wavefield) and the energy spectrum of the source functionThe product of (a) represents.

If one wants to get the correct reflection response estimate by equation 1, one would like to have the same spectrumThe detector is illuminated from all possible angles with a uniform distribution of passive sources. In practice, however, the passive sources are distributed relatively sparsely or in clusters. In this case, in the first embodiment of the present application, equation 1 is discretized and approximated:

wherein the content of the first and second substances,is represented by x_sCross correlation function of a single passive source of (a):

from equations 2 and 3, it can be further understood that for x_sA single passive source of two detectors x_AAnd x_BGreen's function in between:

however, the energy spectrum of the source function is contained in equation 4The term is transformed as a function of the source, and is a complex function of frequency. In actual data processing, the energy spectrum of the source function is difficult to estimate, and therefore, the effect of interference imaging is influenced to a certain extent. However, the detector x_AAnd x_BTo receive wave fieldAndthe deconvolution of (d) is:

whereinIs composed ofThe autocorrelation of (3). As can be seen from the equation 5,are cancelled out, so that when deconvolution interference is carried out, the estimation of a seismic source function is not needed, thereby improving the resolution and the signal-to-noise ratio of interference imaging.

And secondly, performing oblique superposition processing on the deconvolution function, and extracting ray parameters corresponding to the peak value at the zero moment to obtain the effective illumination information direction.

In the case of non-uniform passive source distribution, the difficulty with passive source interferometric imaging is the lack of a portion of the energy used to reconstruct a correct reflective response. The inability to effectively suppress interference artifacts results in non-ideal offset imaging of the deconvolution function. The scattered wavefield, which is radiated from a passive source and reflected from a free surface, carries a large amount of information about the subsurface. In this regard, in the first embodiment of the present application, two direct wave ray paths of the deconvolution function of the known virtual source position are extracted to constrain the subsequent migration processing.

Fig. 2 shows how the reflection response between two detectors is reconstructed. Wherein, the triangle represents the detector, and the five-pointed star represents the passive source. It can be seen that the direct wave radiated by the seismic source in the phase-stable point region reaches one detector and then reaches the other detector through mirror reflection, and the ray paths all include the detector x where the virtual seismic source is located_s. In a laterally homogeneous medium, for each passive source-virtual seismic source pair, there is a specific ray parameter to determine the specular ray. This ray parameter defines the direction of the mirrored ray from the virtual source. In order to find the ray path of the stationary phase point region, only the ray parameter needs to be extracted, and the passive source x does not need to be known_sThe position of (a).

In conventional linear slant stacking, the seismic data may be represented by the operator form equation d ═ Lm, where d is the raw time domain seismic data, m is the radon model, and L is the radon transform operator defined by the observation system and model parameters. The traditional least square oblique superposition method is obtained by solving the minimum extreme value of a cost function:

where λ is the damping factor that controls the degree of roughness of the solution to the equation. radon modelIs solved as m ═ L by least squares^TL+λI)^-1L^Td, wherein I is an identity matrix.

As the seismic data are acquired in a limited space, summation can be carried out only in a limited space-time domain, and the same damping factors are adopted for all frequencies, the energy mass of the radon model cannot be well focused, and the resolution of the result obtained by the method is low. In order to improve the resolution of the radon model, in the first embodiment of the present application, an iterative threshold shrinking algorithm that iterates in the time domain is adopted:

m_k＝T_α{m_k-1+2tF^-1[(L^TL)^-1L^T(F[d]-LF[m_k-1])]} (7)

where k is the number of iterations, m_kIs a time domain radon model after iterating for k times; f and F^-1Respectively representing positive and negative Fourier transformation; t is the step length for controlling the convergence speed, and is usually selected from 0-1; t is_aIs the 2D model convergence operator, a is the operator that controls the threshold contraction in each iteration, usually 0<α<1。

Analysis of ray parameter distribution of deconvolution function by deconvolution function in time domainHigh-resolution linear oblique superposition is performed. When t is 0:

where p is the ray parameter vector, x_H,ARepresents x_AThe horizontal coordinate of (a) of (b),is a virtual seismic source x_BThe ray parameter distribution of the deconvolution function of (2). Wherein the dominant ray parameters define the effective illumination information direction of the virtual source wavefield:

and thirdly, performing offset imaging processing on the virtual shot gather record based on the deconvolution function and the effective illumination information direction to obtain an offset imaging result and finish passive source interference offset imaging.

Obtaining correct imaging results from the deconvolution function with specific ray parameters requires a direction constraint based offset imaging process. In this first embodiment, the imaging conditions are represented by cross-correlation of the forward and backward wavefields, excited from the virtual source and detector locations, respectively. In the embodiment, the green's function in the medium is reconstructed by using the high-frequency progression of Gaussian beams, and the wave field in the medium is approximately represented by overlapping the Gaussian beams in all directions. Each gaussian beam is represented by the ray center coordinates s (x) and n (x) at an arbitrary position x next to the beam in the medium, and in the prior art, in 3D medium, point x_BAnd any point x by each Gaussian beamThe integrals in different directions (described by the azimuth angle theta and the polar angle phi). The expression is as follows:

where the ray center coordinates s and n define the observation position x around which the beam passes.Representing the initial amplitude of the gaussian beam. The behavior of a gaussian beam can be controlled by its width and curvature. These parameters are determined at the detector location.

In the case of a passive source that uniformly illuminates the detector, the forward propagating field should radiate to all angles in the migration process. However, deconvolution function for offset single passive sourceIn other words, the forward wave field should be constrained to the effective illumination information direction. By using the previously described illumination analysis results, the forward wave field of the deconvolution function is illumination direction constrained. Using the velocity c of the medium at the location of the virtual source_p(x_B) Converting the coordinates of the deconvolution function from the ray parameters to angular coordinates:wherein the horizontal slowness coordinates of the ray parametersFor virtual seismic source at x_BThe green's function estimated at x is approximated with a directional constraint by normalizing the ray parameter distribution of the deconvolution functionThe weighting is implemented as follows:

the formula can be derived by constraining the illumination direction to the maximum value reached by the ray parameter distributionThe process is simplified as:

therefore, the temperature of the molten metal is controlled,gaussian beam in the direction of direct wave radiated by passive sourceAnd (4) constructing.

Forward wavefield at time t(or called a down-going wavefield)) At virtual source location x_BIs generated, as represented by the green's function approximation of equation 8:

whereinRepresenting the source function of the active source. The source function may be estimated from the direct arrival of the wavefield based on the transient characteristics of the passive source, or the autocorrelation of the seismic recording may beThe approximation is as a function of the source.

For the back propagation of the detector wavefield, we construct a progressive form of the deconvolution function using the gaussian beam approximation in equation 6, and adjust the kirchhoff integral to x_ADetector boundary at (b):

thus, the backward wavefield (or up-going wavefield) at time t) Gaussian beam function by superimposing deconvolution functions in all directions at xTo calculate:

up going wave fieldIncluding deconvolution functionsProviding autocorrelation of the source signal.

The back propagation estimation of the deconvolution function is different from the forward wave field, and the construction of the back propagation wave field does not need special direction constraint.

Two wave fieldsAndthe zero time delay cross correlation is the imaging condition of the offset

WhereinIs composed of a passive source x_sExcitation at x_BThe virtual source at (a) illuminates the resulting local imaging. And superposing the imaging results obtained by the virtual seismic source at each position to obtain a final imaging result:

the results obtainedIllustrating that the subsurface local medium can be obtained by using a single passive source x_sThe information of the constraint ray parameters contained in (1) is accurately imaged.

Example two

Fig. 3 is a schematic structural diagram of a passive source interference shift imaging system based on illumination direction constraint according to a second embodiment of the present application, including a deconvolution module, an illumination analysis module, and an imaging module.

The deconvolution module is used for carrying out interference processing on the seismic record of the single-point pulse type passive source to obtain a deconvolution function, and the deconvolution function is used for obtaining a virtual shot gather record; the illumination analysis module is used for carrying out oblique superposition processing on the deconvolution function and extracting ray parameters corresponding to peak values at zero time to obtain effective illumination information directions; and the imaging module is used for carrying out offset imaging processing on the virtual shot gather record according to the deconvolution function and the effective illumination information direction to obtain an offset imaging result.

Further, the imaging module consists of a forward wave field unit, a backward wave field unit and an offset imaging unit, wherein the forward wave field unit is used for obtaining a forward wave field according to a deconvolution function and an effective illumination information direction; the back propagation wave field unit is used for constructing a Gaussian beam function based on a deconvolution function and superposing the Gaussian beam function to obtain a back propagation wave field; and the offset imaging unit is used for obtaining an offset imaging result according to the forward transmission wave field and the backward transmission wave field.

The above-described embodiments are merely illustrative of the preferred embodiments of the present application, and do not limit the scope of the present application, and various modifications and improvements made to the technical solutions of the present application by those skilled in the art without departing from the spirit of the present application should fall within the protection scope defined by the claims of the present application.