Method and device for acquiring seismic diffraction body

Abstract

The invention belongs to the technical field of seismic data acquisition and processing, and particularly relates to a method and a device for acquiring a seismic diffraction body. The method comprises the following specific steps: preprocessing collected seismic data to obtain seismic shot gather data which can be directly used for migration; eliminating residual noise by using a multi-channel singular spectrum analysis technology to obtain optimized pre-stack gather data; a complete diffracted wave is obtained through forward and reverse transformation of a virtual seismic source and through offset-reflected wave removal-deoffset; and finally, accurately separating weak signals of the diffracted waves under the condition of intersection and tangency of seismic wave fields by researching characteristics that the polarity and the amplitude of the diffracted waves change along with an emergence angle and an azimuth angle, thereby realizing high-resolution diffraction body imaging of the fractured-vuggy reservoir, effectively improving the imaging precision of the karst fractured-vuggy reservoir, and achieving the purpose of fine detection of the fractured-vuggy reservoir. The method is of positive significance to clarify the seismic response of the fracture-vug type reservoir, implement fracture-vug distribution characteristics and guide effective identification of the karst type reservoir and optimization of a favorable target area.

Description

Technical Field

[0001] The invention belongs to the technical field of seismic data acquisition and processing, and in particular relates to a method and device for acquiring a seismic diffractor. Background Art

[0002] In the late Proterozoic and early Paleozoic, many basins in China deposited thick carbonate rocks, mainly limestone, followed by dolomitic limestone. This type of karst reservoir is diverse in type, with relatively developed fractures and dissolution holes. Wells have been drilled to show that this fracture-hole reservoir has great natural gas exploration potential. Due to the deep carbonate fracture-hole reservoir's deep burial depth, small scale, and strong heterogeneity, the seismic wave field response is manifested as diffraction waves with weak signals, making seismic imaging, fine identification, and characterization difficult.

[0003] With the continuous deepening of reservoir prediction research, the domestic industry has realized that it is necessary to further improve the accuracy of reservoir prediction, such as the internal structure of fault-karst bodies, the filling properties of fracture-cavity bodies, etc. Among them, improving the seismic imaging effect of the reservoir is the basis, such as high-resolution diffraction wave imaging technology. However, how to achieve the separation of pre-stack diffraction waves and reflection waves is a current technical difficulty. Some existing pre-stack diffraction wave separation technologies have high requirements for the signal-to-noise ratio of diffraction waves in the data. When the diffraction wave energy is weak and it is impossible to identify it through the characteristic differences between the diffraction wave and the reflection wave, these methods are difficult to work. For post-stack diffraction wave imaging, how to perform velocity analysis and imaging on the diffraction wave to improve the imaging resolution is the key. In contrast, on the basis of obtaining high-precision seismic imaging effects, improving the characterization technology of small-scale geological bodies is the key to subsequent development and production.

[0004] The series of technologies currently under development, including discontinuity attributes and amplitude attributes, all contain the influence of seismic wavelets, so the vertical resolution is poor, which makes it difficult to accurately judge the depth of the reservoir, especially in the deployment of side drilling and horizontal wells. A Chinese invention patent application with application publication number CN113945968A discloses a diffraction wave imaging method, device and electronic equipment for a discontinuous geological body. Based on the seismic data of the geological body to be measured, characteristic parameters of the seismic data are determined, and then the diffraction wave data of the geological body to be measured is determined based on the characteristic parameters. Finally, the geological body to be measured is imaged based on the diffraction wave data, so as to improve the quality of the diffraction wave imaging of the discontinuous geological body; a Chinese invention patent application with application publication number CN108594303A discloses a diffraction wave attribute extraction method for post-stack seismic data. The seismic data is first pre-processed, a forward model is established according to the actual data, the optimal parameters and the dimensions of the principal components when extracting the diffraction waves by the principal component analysis technology are determined by calculation, the eigenvector calculation formula is improved to be applicable to the calculation formula of three-dimensional seismic data, and the optimal parameters and the dimensions of the principal components are used to extract the diffraction wave field in the actual seismic data, so as to realize the extraction of the diffraction wave field in the post-stack seismic data.

[0005] Although the above existing technologies can separate the diffraction waves, they cannot accurately separate the weak diffraction wave signals when the seismic wave fields are crossed or tangent. Summary of the invention

[0006] The object of the present invention is to provide a method and device for obtaining seismic diffractometers, so as to solve the problem that the existing conventional seismic imaging method cannot accurately separate the weak signals of diffracted waves when the seismic wave fields are crossed and tangent.

[0007] In order to solve the above technical problems, the present invention provides a method for obtaining a seismic diffractometer, comprising the following steps:

[0008] 1) Collect and process the seismic wave field data of the measured area to obtain optimized pre-stack gather data;

[0009] 2) Performing common virtual source forward transformation on pre-stack gather data to obtain common virtual source gather data in which reflection waves are arranged in sequence as linear event axes and diffraction waves are curved; then performing migration processing on the common virtual source gather data to converge the hyperbolic diffraction waves in the common virtual source gather data, then filtering out the reflection waves, and then performing de-migration processing and common virtual source inverse transformation on the data after filtering out the reflection waves, and finally obtaining three-dimensional shot gather diffraction wave data;

[0010] 3) Based on the obtained three-dimensional shot-gather diffraction wave data and the constructed diffraction wave imaging operator, the seismic diffraction volume of the fracture-cavity reservoir is obtained.

[0011] Its beneficial effects are as follows: considering that the existing conventional seismic imaging methods cannot accurately separate the weak signals of diffraction waves under the conditions of intersection and tangency of seismic wave fields, resulting in low resolution of the imaged diffractors and imprecise detection of fracture-cavity reservoirs. The present invention firstly adopts pre-processing and virtual source forward and reverse transformation for the collected seismic wave field data, obtains complete diffraction waves through offset-reflection wave removal-anti-drift, and then uses the characteristics of diffraction wave polarity and amplitude variation with the exit angle and azimuth angle to accurately separate the weak signals of diffraction waves under the conditions of intersection and tangency of seismic wave fields, obtains high-resolution diffractors, and achieves the purpose of fine detection of fracture-cavity reservoirs, so as to clarify the seismic response of fracture-cavity reservoirs, implement the distribution characteristics of fractures and caves, and guide the effective identification of karst reservoirs and the selection of favorable target areas, which has positive significance.

[0012] Furthermore, the processing of the collected seismic wave field data in step 1) includes preprocessing and eliminating residual noise after the preprocessing.

[0013] The beneficial effects are: preprocessing the obtained seismic wave field data and eliminating the residual noise, reducing the influence of the noise on the effective wave, facilitating the analysis of the diffraction wave, and obtaining a high-resolution diffractor.

[0014] Furthermore, the preprocessing includes: observation system information loading, noise removal, field static correction and center point gather sorting.

[0015] The beneficial effects are: eliminating the interference of surface waves, facilitating the analysis of the weak signal of deep karst diffraction waves, extracting the required diffraction wave signals, and obtaining high-resolution diffractometers.

[0016] Furthermore, the residual noise includes residual surface waves, hanging noodle noise and random interference.

[0017] Furthermore, a multi-channel singular spectrum analysis method is used to remove the remaining noise.

[0018] Its beneficial effects are: utilizing the low-rank characteristic of the effective wave signal and optimizing the rank based on the curvature of the singular value curve. This method takes into account the dynamic properties of the diffraction wave and can effectively protect its amplitude and phase characteristics.

[0019] Furthermore, in step 2), a Stolt processing method is used to perform an offset process and an inverse Stolt processing method is used to perform an inverse offset process.

[0020] The beneficial effect is that the reflected waves in the data after the common virtual source forward transformation are filtered out, which is conducive to separating the diffraction waves from the reflected waves, so as to obtain high-resolution diffraction bodies and achieve the purpose of fine detection of fracture-cavity reservoirs.

[0021] Furthermore, when constructing the diffraction wave imaging operator in step 3), for the discontinuous geological structures of faults and small-scale fractures and caves with a certain direction distribution, the amplitude values ​​are imaged using non-mean weighting, and the imaging formula is:

[0022]

[0023] Among them, V1(x) is the diffraction wave imaging result using non-mean weighting method, is the maximum azimuth value, is the minimum azimuth angle value, θ is the exit angle, θ min ,θ max are the minimum and maximum emission angles respectively, x is the underground imaging point, The imaging data of the angular channel is It represents the diffraction wave amplitude coefficient in the angle domain and is calculated as follows:

[0024]

[0025] in, is the azimuth angle, θ is the angle of incidence, and θ is the angle of incidence. s ,θ g , λ is the wavelength and i is an imaginary number.

[0026] The beneficial effects are: improving the focusing, signal-to-noise ratio and breakpoint and cave characterization accuracy of diffraction wave imaging, and clear "beads" can be observed near the target layer. These "beads" reveal the existence of the reservoir, which is of positive significance for implementing the distribution characteristics of fractures and caves, guiding the effective identification of karst reservoirs and optimizing favorable target areas.

[0027] Furthermore, when constructing the diffraction wave imaging operator in step 3), for the inhomogeneous geological body whose spatial distribution is less than one Fresnel zone, the amplitude value is imaged by using mean weighting, and the imaging formula is:

[0028]

[0029] Among them, V2(x) is the diffraction wave imaging result using mean weighted imaging, is the maximum azimuth value, is the minimum azimuth angle value, θ is the exit angle, θ min ,θ max are the minimum and maximum emission angles respectively, x is the underground imaging point, It is the imaging data of the angle channel.

[0030] The beneficial effects are: improving the focusing, signal-to-noise ratio and breakpoint and cave characterization accuracy of diffraction wave imaging, and clear "beads" can be observed near the target layer. These "beads" reveal the existence of the reservoir, which is of positive significance for implementing the distribution characteristics of fractures and caves, guiding the effective identification of karst reservoirs and optimizing favorable target areas.

[0031] To solve the above technical problem, the present invention also provides a device for obtaining a seismic diffractor, comprising a memory and a processor, wherein the processor is used to execute computer program instructions stored in the memory to implement the above-mentioned method for obtaining a seismic diffractor.

[0032] The beneficial effect is that the device ensures the effective and reliable execution of a method for obtaining seismic diffractors. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of the method for obtaining seismic diffractors of the present invention;

[0034] Figure 2 It is a schematic diagram of the diffraction wave recording separated by the conventional method in the test area of ​​the present invention;

[0035] Figure 3 It is a schematic diagram of recording diffraction waves separated by the method of the present invention in the test area of ​​the present invention;

[0036] Figure 4 This is a cross-sectional effect diagram of the karst crack-cave body imaged by reflection wave in the test work area of ​​the present invention;

[0037] Figure 5 It is a cross-sectional effect diagram of the karst fracture-cave body imaged by diffraction waves in the test work area of ​​the present invention. DETAILED DESCRIPTION

[0038] The basic concept of the present invention is as follows: the present invention first pre-processes the collected seismic data to obtain seismic shot gather data that can be directly used for migration; then uses a multi-channel singular spectrum analysis technology to eliminate residual noise and obtain optimized pre-stack gather data; uses virtual source forward and inverse transformations to obtain complete diffraction waves through migration-reflection wave removal-anti-migration; finally, by studying the variation characteristics of diffraction wave polarity and amplitude with the emergence angle and azimuth angle, high-resolution diffraction body imaging of fracture-cavity reservoirs is achieved, and the imaging accuracy of karst fracture-cavity bodies is effectively improved.

[0039] The present invention will be described in detail below with reference to the accompanying drawings and method embodiments.

[0040] Method Example:

[0041] This method embodiment takes the 3D seismic data processing of a certain work area in a certain basin as an example. It is known that the scope of the study area is 50km 2, belonging to the desert steppe landform, the terrain is relatively complex, the surface is undulating, the local height difference is tens of meters, the floating sand is thick, and the lateral velocity changes dramatically; the geological background of the study area is monocline structure, and the seismic data show that the Paleozoic strata are extremely flat monocline, the Paleozoic strata dip angle is less than 10°, the burial depth is about 2,800 meters, there are no large stress structures, and the faults are not developed; there are about 6 completed wells (including exploration wells, vertical wells, and horizontal wells) in the study area, and the well points are relatively sparsely distributed. Due to the deep burial depth, the diffraction wave energy distribution range is large and the diffraction wave energy is weak, and it is difficult to identify it through the characteristic differences between the diffraction wave and the reflection wave, and conventional methods are difficult to work.

[0042] In order to solve the problem that the diffraction wave energy distribution range is large and the diffraction wave energy is weak due to the above-mentioned geographical environment, and it is impossible to identify the diffraction wave and the reflected wave through the characteristic difference, a method for obtaining a seismic diffractor is provided in the present invention, and the flow chart is as follows: Figure 1 As shown, the specific implementation steps include:

[0043] Step 1: Perform a series of preprocessing on the collected seismic data to obtain three-dimensional shot gather data that can be directly used for migration.

[0044] 1) Deploy a seismic acquisition system in the research area to collect and acquire three-dimensional seismic data in the research area;

[0045] 2) The noise frequency band in the pre-stack gather is wide, often overlapping with the effective wave; the energy is strong, and the noise energy covers the effective signal; the linear law of other noises such as surface waves is not strong, it is difficult to suppress, and there are residuals, which is not conducive to the analysis of weak signals of deep karst diffraction waves. Through industrial seismic data processing software, the collected 3D seismic data is loaded with observation system information such as shot points and detection points, and the noise module is used to remove interference such as surface waves; and a series of seismic data standard preprocessing such as field static correction and center point gather sorting are implemented to obtain 3D shot gather data that can be directly used for migration.

[0046] Step 2: Use multi-channel singular spectrum analysis technology to eliminate residual noise and obtain optimized pre-stack gather data.

[0047] Due to the complex geological conditions in the research area, the three-dimensional shot gather data obtained in step one has a low signal-to-noise ratio, and even after denoising, it still contains residual noise (the residual noise mainly includes three types: residual surface waves, hanging noodle noise and random interference). Therefore, the present invention is based on a residual noise removal method with low rank constraints based on multi-channel singular spectrum analysis to remove the residual noise remaining in the three-dimensional shot gather data and obtain optimized three-dimensional shot gather data. In the pre-stack gather, the size of the singular value is proportional to the energy intensity of the linear signal. The stronger the energy of the effective signal component, the larger the corresponding singular value. Utilizing the low-rank characteristics of the effective wave signal, the rank is optimized based on the curvature of the singular value curve, and the singular values ​​and singular vectors corresponding to the effective wave are selected to restore the effective wave signal. The specific multi-channel singular spectrum analysis technology calculation includes the following steps:

[0048] 1) The time domain seismic data d t (x, t) is converted into frequency domain data d f (x,f):

[0049]

[0050] 2) Construct the Hankel matrix as follows:

[0051]

[0052] Among them, N x is the number of sampling points of seismic data in the x direction. m and n are two important parameters for constructing the square Hankel matrix. Generally, n=INT(N / 2)+1 and m=N-n+1. INT(·) represents the integer part of the element in brackets.

[0053] 3) Apply singular value decomposition technology to decompose the constructed Hankel matrix. The decomposition process is as follows:

[0054]

[0055] Where Ω represents the singular value σ of the effective signal i A and B represent matrices composed of singular vectors, r is the rank of the effective signal, and the symbol (·) H Represents the conjugate transpose operation of the matrix. The size of the singular value after signal decomposition is directly related to the energy of its corresponding signal component. The stronger the energy of the signal component, the larger the corresponding singular value, and vice versa. Therefore, in order to eliminate the noise component in the seismic data, the truncated SVD algorithm can be used to select some larger singular values ​​to reconstruct the Hankel matrix of the signal to achieve the purpose of removing noise.

[0056] Step three, use the common virtual source transformation to generate a new gather, and then use migration-reflection wave removal-anti-migration to finally obtain the three-dimensional shot gather diffraction wave data through the common virtual source inverse transformation.

[0057] The common shot point gather data is transformed into a common virtual source by giving coordinates point by point. The reflection events from the same reflection surface will be corrected to the same virtual source, but the reflected waves are not focused and superimposed at the virtual source position, but are arranged in sequence to form linear phase axes. Since the diffraction wave has no virtual source, the diffraction wave will not appear as a horizontal line in the common virtual source gather, but as a curved shape. Therefore, the common virtual source gather data is obtained by using the common virtual source transformation on the optimized three-dimensional shot gather data. The Stolt migration method is used on the common virtual source gather data to converge the hyperbolic diffraction waves in the common virtual source gather data. The regularized plane wave destruction filtering method is used to remove the reflected waves in the common virtual source data after the migration. The Stolt inverse migration is used on the data after the reflection waves are removed to obtain the weak signal of the diffraction wave in the common virtual source gather data. Finally, the three-dimensional diffraction wave data is obtained by the common virtual source inverse transformation.

[0058] The diffraction wave separation results are obtained based on the traditional plane wave destruction filter method. Figure 2 As shown by the arrow, the diffraction wave is severely damaged in the figure, and the diffraction wave separation problem in the case of wave field intersection or tangency cannot be handled well. In the regularized plane wave destruction filtering method of the present invention, the window for dip estimation is set to 20 sample points, and the final technical effect is as follows Figure 3 As shown by the arrows, it is obvious that the separated diffraction waves are more complete, especially the diffraction top.

[0059] Step 4: construct a diffraction wave imaging operator to obtain the seismic diffraction volume of the fracture-cavity reservoir.

[0060] The diffracted body imaging formula is as follows:

[0061]

[0062] Among them, V(x) is the diffraction wave imaging result, is the maximum azimuth value, is the minimum azimuth angle value, θ is the exit angle, θ min ,θ max are the minimum and maximum emission angles respectively, x is the underground imaging point, The imaging data of the angular channel is It represents the diffraction wave amplitude coefficient in the angle domain and is calculated as follows:

[0063]

[0064] in, is the azimuth angle, θ is the angle of incidence, and θ is the angle of incidence. s ,θg , λ is the wavelength and i is an imaginary number.

[0065] The present invention is completed on the basis of the basic principle of three-dimensional seismic exploration, that is, the diffraction waves received by the ground detector are mainly related to small-scale geological bodies such as faults and karst caves. The energy of the diffraction wave decays very quickly, and the attenuation mode is related to the exit angle and azimuth. The diffraction waves from the breakpoints (faults, etc.) and the diffraction waves from the scattering points (karst, caves, etc.) in the three-dimensional angle domain have different inclination and azimuth characteristics. The diffraction waves from the scattering points are distributed in a wide range of azimuth and inclination; while the diffraction waves from the breakpoints are distributed in a wide range of inclination and limited azimuth.

[0066] Based on the above principle, the present invention constructs the first imaging condition of the three-dimensional angle domain diffraction wave dynamic imaging method: mainly for discontinuous geological structures such as faults and small-scale fractures and caves with a certain direction distribution. At this time, the diffraction wave has polarity reversal and amplitude advantage azimuth characteristics. Through this imaging mechanism, the diffraction wave energy can be fully utilized to clearly depict the interior and boundary morphology of the geological structure. According to the first part of the imaging formula (containing the angle domain diffraction wave amplitude coefficient), the amplitude value is subjected to non-mean weighted imaging; the second imaging condition: mainly for inhomogeneous geological bodies with a spatial distribution smaller than a Fresnel zone, such as small-scale karst caves, etc., because their diffraction wave energy is approximately uniformly distributed in the three-dimensional angle domain, the amplitude value is imaged using mean weighting. Using the constructed diffraction wave imaging operator, the technical effects obtained are as follows: Figure 5 As shown in Figure 2, compared with traditional reflection wave imaging technology, Figure 4 As shown, the present invention improves the focusing, signal-to-noise ratio and accuracy of characterization of breakpoints and caves in diffraction wave imaging, and clear "beads" can be observed near the target layer. These "beads" reveal the existence of the reservoir and clarify the seismic response of the fracture-cavity reservoir, which is of positive significance for implementing the distribution characteristics of fractures and caves, guiding the effective identification of karst reservoirs and optimizing favorable target areas.

[0067] Device Example:

[0068] A device for obtaining a seismic diffractor of the present invention comprises a memory and a processor, wherein the processor is used to execute computer program instructions stored in the memory to implement a method for obtaining a seismic diffractor described in the method embodiment of the present invention. The processor may be a processing device such as a programmable logic device FPGA. The memory may be various memories that use electrical energy to store information, such as RAM, ROM, etc., or may be other types of memories.

Claims

1. A method for obtaining a seismic diffractometer, characterized in that: The steps include: 1) Collect and process the seismic wave field data of the measured area to obtain optimized pre-stack gather data; 2) Performing common virtual source forward transformation on pre-stack gather data to obtain common virtual source gather data in which reflection waves are arranged in sequence as linear event axes and diffraction waves are curved; then performing migration processing on the common virtual source gather data to converge the hyperbolic diffraction waves in the common virtual source gather data, then filtering out the reflection waves, and then performing de-migration processing and common virtual source inverse transformation on the data after filtering out the reflection waves, and finally obtaining three-dimensional shot gather diffraction wave data; 3) Based on the obtained three-dimensional shot-gather diffraction wave data and the constructed diffraction wave imaging operator, the seismic diffraction volume of the fracture-cavity reservoir is obtained.

2. The method for obtaining seismic diffractors according to claim 1, characterized in that: The processing of the collected seismic wave field data in step 1) includes preprocessing and eliminating the residual noise after the preprocessing.

3. The method for obtaining seismic diffractors according to claim 2, characterized in that: Preprocessing includes: Observation system information loading, noise removal, field static correction and center point gather sorting.

4. The method for obtaining seismic diffractors according to claim 2, characterized in that: The remaining noise includes residual surface waves, hanging noodle noise and random interference.

5. The method for obtaining seismic diffractors according to claim 4, characterized in that: Multi-channel singular spectrum analysis method is used to remove the remaining noise.

6. The method for obtaining seismic diffractors according to claim 1, characterized in that: In step 2), the Stolt processing method is used for offset processing and the inverse Stolt processing method is used for inverse offset processing.

7. The method for obtaining seismic diffractors according to claim 1, characterized in that: When constructing the diffraction wave imaging operator in step 3), for the discontinuous geological structures of faults and small-scale fractures and caves with a certain direction distribution, the amplitude values ​​are imaged using non-mean weighting, and the imaging formula is: Among them, V1(x) is the diffraction wave imaging result using non-mean weighting method, is the maximum azimuth value, is the minimum azimuth angle value, θ is the exit angle, θ min ,θ max are the minimum and maximum emission angles respectively, x is the underground imaging point, The imaging data of the angular channel is It represents the diffraction wave amplitude coefficient in the angle domain and is calculated as follows: in, is the azimuth angle, θ is the angle of incidence, and θ is the angle of incidence. s ,θ g , λ is the wavelength and i is an imaginary number.

8. The method for obtaining seismic diffractors according to claim 1, characterized in that: When constructing the diffraction wave imaging operator in step 3), for the inhomogeneous geological body whose spatial distribution is less than one Fresnel zone, the amplitude value is imaged by mean weighting, and the imaging formula is: Among them, V2(x) is the diffraction wave imaging result using mean weighted imaging, is the maximum azimuth value, is the minimum azimuth angle value, θ is the exit angle, θ min ,θ max are the minimum and maximum emission angles respectively, x is the underground imaging point, It is the imaging data of the angle channel.

9. A device for obtaining seismic diffractors, characterized in that: The method comprises a memory and a processor, wherein the processor is used to execute computer program instructions stored in the memory to implement the method for obtaining a seismic diffractor according to any one of claims 1 to 8.

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