A method and system for evaluating reliability of slowness accumulation acceleration field

Abstract

The application provides a slowness accumulation velocity field reliability evaluation method and system, the evaluation method comprises the following steps: using the relative change keeping thought of a velocity field, combining wave field continuation migration and rational approximation dispersion equation, and establishing the relationship between the wave field continuation operator and the migration velocity field; using the slowness accumulation item in the continuation operator to calculate the slowness matrix, and extracting the slowness accumulation curve of the migration velocity field to quantitatively depict the internal structure of the migration velocity field; using the cross-correlation function to calculate the similarity coefficient between the slowness accumulation curves of different original velocity fields and different migration velocity fields; using the slowness accumulation relative error and the migration result residual as constraints, and using the similarity coefficient of the slowness accumulation curve to represent the accuracy of the velocity field. The accuracy of the migration velocity field is efficiently and accurately determined.

Description

Technical Field

[0001] This invention relates to the field of seismic data processing for oil and gas exploration, and particularly to a method and system for evaluating the reliability of slow-accumulation velocity fields. Background Technology

[0002] Currently, based on different judgment criteria, velocity field reliability assessment methods can be divided into the following two categories: ① Methods that use migration velocity fields for simulation, with the optimal fit between the forward modeling results and actual data as the judgment criterion, such as conventional stacking velocity analysis, Deregowski loop velocity analysis using time migration, coherent velocity inversion based on rays, and tomographic inversion velocity analysis; these methods have poor adaptability to lateral velocity variations in formations and are not suitable for obtaining high-precision velocity fields for complex structures. ② Methods that use migration velocities for pre-stack depth migration imaging, judging the correctness of the velocity field by evaluating the quality of the migration imaging results, such as velocity analysis based on confocal points (CFP), depth focusing analysis (DFA), and residual curvature analysis (RCA). Because pre-stack depth migration requires generating common imaging point gathers, this type of method has always faced a series of challenges such as high computational cost and low efficiency.

[0003] The distribution of velocity always implies information about the distribution of subsurface structures, and velocity distortion inevitably leads to structural distortion in the imaging. High-quality seismic imaging results require high-quality seismic data, high-precision seismic migration algorithms, and accurate migration velocity fields as constraints. The uncertainty of the migration velocity field largely restricts the repositioning and focusing of seismic waves during the migration process, seriously affecting the quality of seismic migration imaging. Therefore, it is particularly important to analyze the intrinsic structure of the velocity field and explore methods for evaluating its accuracy.

[0004] Currently used methods for evaluating the correctness of velocity fields have some effectiveness, but they are either inefficient or require pre-stack depth migration to generate common imaging point gathers, which involves a large amount of computation and makes it difficult to meet the needs of efficient and accurate evaluation of velocity fields. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a method and system for reliability evaluation of slow-accumulation velocity fields that overcomes or at least partially solves the above problems.

[0006] According to one aspect of the present invention, a method for evaluating the reliability of a slow-accumulation velocity field is provided, the evaluation method comprising:

[0007] By utilizing the concept of maintaining the relative change of the velocity field, and combining wave field extension migration with rational approximation dispersion equations, the relationship between the wave field extension operator and the migration velocity field is established.

[0008] The slowness matrix is ​​calculated using the slowness accumulation term in the extension operator, and the slowness accumulation curve of the offset velocity field is extracted to quantitatively characterize the intrinsic structure of the offset velocity field.

[0009] The similarity coefficient between the slowness accumulation curves of different original velocity fields and the slowness accumulation curves of different offset velocity fields is calculated using the cross-correlation function;

[0010] Using the slow-accumulation relative error and the offset result residual as constraints, the similarity coefficient of the slow-accumulation curve is applied to characterize the accuracy of the velocity field.

[0011] Optionally, establishing the relationship between the wavefield extension operator and the migration velocity field specifically includes:

[0012] The wave field is extended from the Earth's surface to the subsurface using a seismic wave propagation operator, as follows:

[0013]

[0014] Wherein, P(k) x ,z;ω) represents the earthquake record on the Earth's surface, P1(k x ,z+Δz;ω) represents the seismic data of the first underground layer, where z represents depth, ω represents frequency, and Δz is the extension step size. The surface wavefield is extended to the nth underground layer using Equation 1):

[0015]

[0016] Fu Liyun, through his study of the standard one-way wave parabolic equation and the split-step dispersion equation, derived the rational approximation dispersion equation:

[0017]

[0018] Among them, a j (n) and b j (n) is a function of the change in lateral velocity;

[0019] Using equations 2) and 3), the relationship between the extension operator and the migration velocity is established. For the nth wavefield:

[0020]

[0021] As can be seen from Equation 4), the velocity field affects the final migration imaging result through the continuation operator.

[0022] Optionally, the slow accumulation term in the extension operator is and

[0023] Optionally, the calculation of the slowness matrix using the slowness accumulation term in the extension operator specifically includes:

[0024] The slow-order accumulation term in the extension operator and To calculate the target, an inverse proportional operation is performed on the velocity field matrix, and the reciprocal of each point in the matrix is ​​calculated to obtain the deflection velocity field slowness matrix.

[0025] Optionally, the quantitative characterization of the intrinsic structure of the migration velocity field specifically includes:

[0026] By longitudinally accumulating the slowness matrix of the offset velocity field, the corresponding slowness accumulation curve is obtained, which characterizes the topological structure information of the offset velocity field and quantitatively describes the intrinsic structure of the offset velocity field.

[0027] Optionally, the intrinsic structure specifically includes the shape, complexity, and irregularity of the offset velocity field.

[0028] Optionally, before calculating the similarity coefficient between the slowness accumulation curves of different offset velocity fields using the cross-correlation function, the method further includes: performing offset imaging on the velocity field;

[0029] The offset results of the original velocity field and the processed velocity fields with different offset values ​​are subtracted to calculate the corresponding offset result residuals. Similarly, the cumulative relative error of the slowness can be obtained.

[0030] Optionally, the similarity coefficient of the applied slow-accumulation curve, which characterizes the accuracy of the velocity field, specifically includes:

[0031] The similarity coefficient is between 0.8 and 1.0, indicating that the more similar the intrinsic structure of the original velocity field is to the original velocity field, the closer the migration result will be.

[0032] Optionally, the step of calculating the slowness matrix using the slowness accumulation term in the extension operator and extracting the slowness accumulation curve of the migration velocity field to quantitatively characterize the intrinsic structure of the migration velocity field specifically includes:

[0033] The slowness matrix of the offset velocity field is obtained by using the slowness accumulation term in the extension operator as the calculation target through the inverse proportional function. The slowness matrix of the offset velocity field is vertically accumulated using the cumsum function. The slowness accumulation curve of the velocity field is extracted based on the accumulation result. The slowness accumulation curve is used to represent the topological structure information of the offset velocity field and quantitatively characterize the intrinsic structure of the offset velocity field.

[0034] This invention also provides a reliability evaluation system for slow-acceleration fields, which applies the aforementioned reliability evaluation method for slow-acceleration fields. The evaluation system includes:

[0035] The module for establishing the relationship between the operator and the velocity field is used to establish the relationship between the wave field extension operator and the migration velocity field by utilizing the idea of ​​maintaining the relative change of the velocity field and combining the wave field extension migration and the rational approximation dispersion equation.

[0036] The intrinsic structure characterization module of the velocity field is used to calculate the slowness matrix using the slowness accumulation term in the extension operator and extract the slowness accumulation curve of the offset velocity field to quantitatively characterize the intrinsic structure of the offset velocity field.

[0037] The similarity coefficient calculation module is used to calculate the similarity coefficient between the slowness accumulation curves of different original velocity fields and the slowness accumulation curves of different offset velocity fields using the cross-correlation function;

[0038] The velocity field accuracy characterization module is used to characterize the accuracy of the velocity field by applying the similarity coefficient of the slow-accumulation curve, with the slow-accumulation relative error and the offset result residual as constraints.

[0039] This invention provides a method and system for evaluating the reliability of a slow-accumulation velocity field. The evaluation method includes: establishing the relationship between the wavefield extension operator and the migrated velocity field by utilizing the concept of maintaining the relative change of the velocity field and combining wavefield extension migration with rational approximation dispersion equations; calculating the slowness matrix using the slowness accumulation term in the extension operator and extracting the slowness accumulation curve of the migrated velocity field to quantitatively characterize the intrinsic structure of the migrated velocity field; calculating the similarity coefficient between the slowness accumulation curves of different original velocity fields and the slowness accumulation curves of different migrated velocity fields using a cross-correlation function; and using the relative error of slowness accumulation and the residual of the migration result as constraints, applying the similarity coefficient of the slowness accumulation curve to characterize the accuracy of the velocity field. This method efficiently and accurately determines the precision of the migrated velocity field.

[0040] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a flowchart of a method for evaluating the reliability of a slow-accumulation velocity field, provided as an embodiment of the present invention. Detailed Implementation

[0043] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0044] The terms "comprising" and "having," and any variations thereof, in the specification, embodiments, claims, and drawings of this invention are intended to cover non-exclusive inclusion, such as including a series of steps or units.

[0045] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0046] Example 1

[0047] This invention provides a reliability evaluation method for slow-accumulation velocity fields based on wave equation migration, which efficiently and accurately determines the accuracy of the migrated velocity field.

[0048] This invention utilizes the concept of preserving the relative changes in the velocity field. Combining wavefield extension migration with rational approximation dispersion equations, it establishes the relationship between the wavefield extension operator and the migrated velocity field. The slowness matrix is ​​calculated using the slowness accumulation term in the extension operator, and the slowness accumulation curve of the velocity field is extracted to quantitatively characterize the intrinsic structure of the migrated velocity field (i.e., the degree of change in the shape, complexity, and irregularity of the migrated velocity field). Similarity coefficients between the slowness accumulation curves of different migrated velocity fields are calculated using a cross-correlation function. With the relative error of slowness accumulation and the residual of the migration result as constraints, the similarity coefficients of the slowness accumulation curves are applied to characterize the accuracy of the velocity field and achieve a reliability evaluation of the velocity field.

[0049] Basic principles of the invention

[0050] In seismic exploration of complex underground structural areas, it is difficult to accurately determine the migration velocity field, especially in more complex locations such as faults. This can lead to the establishment of erroneous migration velocities. Therefore, it is crucial to quantitatively analyze the relative preservation of the velocity field and characterize the topological structure information of the velocity field.

[0051] The core of seismic migration imaging using the wave equation is wavefield continuation. The velocity field influences the final imaging result through the continuation operator. This invention utilizes wavefield continuation migration and rational approximation dispersion equations to establish the relationship between the wavefield continuation operator and the migration velocity field.

[0052] The slowness matrix of the offset velocity field is obtained by using an inverse proportional function with the slowness accumulation term in the extension operator as the calculation target. The slowness matrix of the offset velocity field is vertically accumulated using the cumsum function. Based on the accumulation result, the slowness accumulation curve of the velocity field is extracted. The slowness accumulation curve is used to represent the topological structure information of the offset velocity field and quantitatively characterize the internal structure of the offset velocity field (i.e., the degree of change in the shape, complexity, and irregularity of the offset velocity field).

[0053] Then, using a cross-correlation function, the similarity coefficient between the original velocity field's slowness accumulation curve and the slowness accumulation curves of different offset velocity fields is calculated. With the relative error of slowness accumulation and the residual of the offset result as constraints, the similarity coefficient of the slowness accumulation curves is applied to quantitatively analyze and characterize the accuracy of the velocity field. The closer the correlation coefficient is to 1 (generally between 0.8 and 1.0), the more similar it is to the original velocity field's intrinsic structure, and the closer the offset result is, thus achieving a reliability evaluation of the velocity field.

[0054] This invention specifically includes the following:

[0055] A reliability evaluation method for slow-accumulation velocity fields based on wave equation migration is implemented as follows:

[0056] 1) Establish the relationship between the wave field extension operator and the offset velocity field.

[0057] The wave field is extended from the Earth's surface to the subsurface using a seismic wave propagation operator, as follows:

[0058]

[0059] Where P(k) x ,z;ω) represents the earthquake record on the Earth's surface, P1(k x ,z+Δz;ω) represents the seismic data of the first underground layer, where z represents depth, ω represents frequency, and Δz is the extension step size. The surface wavefield is extended to the nth underground layer using Equation 1):

[0060]

[0061] Fu Liyun et al., through their study of the standard one-way wave parabolic equation and the split-step dispersion equation, derived the rational approximation dispersion equation:

[0062]

[0063] Among them, a j (n) and b j (n) is a function of the change in lateral velocity.

[0064] Using equations 2) and 3), the relationship between the extension operator and the migration velocity is established. For the nth wavefield:

[0065]

[0066] As shown in Equation 4), the velocity field affects the final migration imaging result through the continuation operator, which includes a slowness accumulation term. and This provides a more direct approach to analyzing the accuracy of imaging quality and the migration velocity field.

[0067] 2) The slow-speed accumulation term in the extension operator and To calculate the target, an inverse proportional operation is performed on the velocity field matrix, and the reciprocal of each point in the matrix is ​​calculated to obtain the deflection velocity field slowness matrix.

[0068] 3) The slowness matrix of the offset velocity field is vertically accumulated to obtain the corresponding slowness accumulation curve, thereby representing the topological structure information of the offset velocity field and quantitatively characterizing the intrinsic structure of the offset velocity field (i.e., the degree of change in the shape, complexity, irregularity, etc. of the offset velocity field).

[0069] 4) Perform migration imaging on the velocity field.

[0070] 5) Subtract the original velocity field from the migration results of the processed velocity fields and calculate the corresponding migration result residuals. Similarly, the cumulative relative error of the slowness can be obtained.

[0071] 6) Calculate the similarity coefficient between the original velocity field slowness accumulation curve and the slowness accumulation curves of different offset velocity fields using the cross-correlation function.

[0072] 7) Using the cumulative relative error of slowness and the residual of the migration result as constraints, the similarity coefficient of the cumulative slowness curve is applied to quantitatively analyze and characterize the accuracy of the velocity field. The closer the correlation coefficient is to 1 (generally between 0.8 and 1.0), the more similar it is to the intrinsic structure of the original velocity field, and the closer its migration result is, thus enabling a rapid evaluation of the reliability of the velocity field.

[0073] Example 2

[0074] like Figure 1 As shown, the reliability evaluation of the offset velocity field is carried out, and the specific process includes:

[0075] 1) Extend the wave field from the surface to the underground through the seismic wave propagation operator and establish the relationship between the extension operator and the migration velocity.

[0076] 2) Using the slow-speed accumulation term in the extension operator and To calculate the target, an inverse proportional operation is performed on the velocity field matrix, and the reciprocal of each point in the matrix is ​​calculated to obtain the deflection velocity field slowness matrix.

[0077] 3) The slowness matrix of the offset velocity field obtained in step 2 is accumulated vertically, and the slowness accumulation curve of the velocity field is extracted based on the accumulation result to represent the topological structure information of the offset velocity field and quantitatively characterize the internal structure of the offset velocity field (i.e., the shape, complexity, irregularity and other changes of the offset velocity field).

[0078] 4) Image the offset velocity field.

[0079] 5) Calculate the slowness cumulative relative error and offset result residual by subtracting the results from the results of steps 3 and 4.

[0080] 6) Calculate the similarity coefficient between the original velocity field slowness accumulation curve and the slowness accumulation curves of different offset velocity fields using the cross-correlation function.

[0081] 7) Using step 5 as an evaluation constraint, and based on the results of step 6, the accuracy of the velocity field is quantitatively analyzed and characterized, and finally the reliability evaluation of the velocity field is achieved.

[0082] Beneficial effects: Reliability of the method. The method of this invention utilizes the concept of maintaining the relative change of the velocity field. Based on the similarity matching of the slow-accumulation curve, it uses the relative error of the slow-accumulation and the residual of the offset result for dual constraints, thus ensuring the reliability and accuracy of the method.

[0083] The method is highly adaptable. The method of this invention can perform topological structure analysis on the offset velocity field obtained by various processing methods (offset velocity field modeling, superimposed velocity analysis, etc.) and complete the reliability evaluation of the offset velocity field.

[0084] The operation is simple and easy to implement. The method and steps of this invention are simple and convenient, and do not require tedious parameter adjustments and tests.

[0085] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A reliability evaluation method for a slow-accumulation velocity field, characterized in that, The evaluation methods include: By utilizing the concept of maintaining the relative change of the velocity field, and combining wave field extension migration with rational approximation dispersion equations, the relationship between the wave field extension operator and the migration velocity field is established. The slowness matrix is ​​calculated using the slowness accumulation term in the extension operator, and the slowness accumulation curve of the offset velocity field is extracted to quantitatively characterize the intrinsic structure of the offset velocity field. The similarity coefficient between the slowness accumulation curves of different original velocity fields and the slowness accumulation curves of different offset velocity fields is calculated using the cross-correlation function; Using the slow-accumulation relative error and the offset result residual as constraints, the similarity coefficient of the slow-accumulation curve is applied to characterize the accuracy of the velocity field. The relationship between the wavefield extension operator and the migration velocity field is established as follows: Establish the relationship between the continuation operator and the migration velocity for the nth wavefield: Formula 4 in, Earthquake records on the Earth's surface. Indicates depth, Indicates frequency, Let be the extension step size; as shown in Equation 4, the velocity field affects the final migration imaging result through the extension operator; The slowness accumulation term in the extension operator is: and ; The calculation of the slowness matrix using the slowness accumulation term in the extension operator specifically includes: The slow-order accumulation term in the extension operator and To calculate the target, an inverse proportional operation is performed on the velocity field matrix, and the reciprocal of each point in the matrix is ​​calculated to obtain the deflection velocity field slowness matrix; The specific structure of the quantitative characterization of the migration velocity field includes: By longitudinally accumulating the slowness matrix of the offset velocity field, the corresponding slowness accumulation curve is obtained, which characterizes the topological structure information of the offset velocity field and quantitatively describes the intrinsic structure of the offset velocity field.

2. The method for reliability evaluation of a slow-accumulation velocity field according to claim 1, characterized in that, The establishment of the relationship between the wavefield extension operator and the migration velocity field also includes: The wave field is extended from the Earth's surface to the subsurface using a seismic wave propagation operator, as follows: Formula 1 in, For seismic data from the first underground layer, the surface wavefield is extended to the nth underground layer using Equation 1: Formula 2 By studying the standard one-way wave parabolic equation and the split-step dispersion equation, a rational approximation dispersion equation is derived: Formula 3 in, and It is a function of the change in lateral velocity; The relationship between the extension operator and the offset velocity is established using Equations 2 and 3.

3. The method for reliability evaluation of a slow-accumulation velocity field according to claim 1, characterized in that, The intrinsic structure specifically includes the shape, complexity, and irregularity of the offset velocity field.

4. The method for reliability evaluation of a slow-accumulation velocity field according to claim 1, characterized in that, Before calculating the similarity coefficient between the slow accumulation curves of different original velocity fields and the slow accumulation curves of different offset velocity fields using the cross-correlation function, the method further includes: performing offset imaging on the velocity field; The offset results of the original velocity field and the processed velocity fields with different offset values ​​are subtracted to calculate the corresponding offset result residuals. Similarly, the cumulative relative error of the slowness can be obtained.

5. The method for reliability evaluation of a slow-accumulation velocity field according to claim 1, characterized in that, The similarity coefficient of the applied slow-accumulation curve, which characterizes the accuracy of the velocity field, specifically includes: The similarity coefficient is between 0.8 and 1.0, indicating that the more similar the intrinsic structure of the original velocity field is to the original velocity field, the closer the migration result will be.

6. A reliability evaluation system for a slow-acceleration field, employing the reliability evaluation method for a slow-acceleration field as described in any one of claims 1-5, characterized in that, The evaluation system includes: The module for establishing the relationship between the operator and the velocity field is used to establish the relationship between the wave field extension operator and the migration velocity field by utilizing the idea of ​​maintaining the relative change of the velocity field and combining the wave field extension migration and the rational approximation dispersion equation. The intrinsic structure characterization module of the velocity field is used to calculate the slowness matrix using the slowness accumulation term in the extension operator and extract the slowness accumulation curve of the offset velocity field to quantitatively characterize the intrinsic structure of the offset velocity field. The similarity coefficient calculation module is used to calculate the similarity coefficient between the slowness accumulation curves of different original velocity fields and the slowness accumulation curves of different offset velocity fields using the cross-correlation function; The velocity field accuracy characterization module is used to characterize the accuracy of the velocity field by applying the similarity coefficient of the slow-accumulation curve, with the slow-accumulation relative error and the offset result residual as constraints.

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