A method and device for predicting fractures based on seismic wave field forward modeling

Abstract

The application provides a method and device for predicting fractures based on seismic wave field forward prediction, a storage medium and an electronic device, and relates to the technical field of oil exploration and development. The method comprises the following steps: obtaining an elastic coefficient matrix of a fractured medium based on a pre-established variable-azimuth fractured rock physics model; performing anisotropic wave equation forward based on the elastic coefficient matrix of the fractured medium to obtain common imaging point angle gather data under different azimuth angles; performing P-wave AVO analysis on the common imaging point angle gather data under different azimuth angles to obtain a correlation coefficient and a most negative gradient direction corresponding to each CDP bin in the common imaging point angle gather data under different azimuth angles; and predicting the development degree and strike of the fractures based on the correlation coefficient and the most negative gradient direction corresponding to each CDP bin. The technical scheme provided by the application can more conveniently and accurately predict fractures.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration and development technology, and in particular to a method and apparatus for predicting fractures based on seismic wavefield forward modeling. Background Technology

[0002] Fractures serve as both reservoirs for oil and gas and pathways for their migration, making their discovery crucial for oil and gas reservoir finding. Vertical fractures exhibit azimuth anisotropy, necessitating the derivation of applicable methods based on the geological conditions of the work area for accurate identification and description. Existing fracture prediction methods are complex to implement and do not consider the influence of azimuth, resulting in low accuracy in oil and gas prediction and failing to meet the needs of high-precision exploration and development in oil fields. Summary of the Invention

[0003] To address the problems in the prior art, this application proposes a method and apparatus for predicting cracks based on seismic wavefield forward modeling, which can more conveniently and accurately predict cracks.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] In a first aspect, embodiments of the present invention provide a method for predicting cracks based on seismic wavefield forward modeling, the method comprising:

[0006] Based on a pre-established rock physics model of variable orientation fractures, the elastic coefficient matrix of the fracture medium is obtained.

[0007] Anisotropic wave equation forward modeling is performed based on the elastic coefficient matrix of the fractured medium to obtain common imaging point corner gather data at different azimuth angles;

[0008] P-wave AVO analysis was performed on the common imaging point corner gather data under different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data under different azimuth angles.

[0009] Based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, the development degree and orientation of the crack are predicted.

[0010] Preferably, the rock physical model of the variable orientation fracture is expressed by the following expression:

[0011]

[0012] Among them, Z N Z represents the normal compliance of the crack. T θ represents the tangential compliance of the fracture; θ represents the fracture azimuth angle; and Z represents the rock physics model of the variable azimuth fracture.

[0013] Preferably, the elastic coefficient matrix of the fractured medium is obtained using the following expression:

[0014] C eff =(M background +Z fractutre1 +Z fractutre2 ) -1

[0015] Among them, C eff M is the elastic coefficient matrix of the fractured medium; background Z represents the compliance coefficient matrix of the fractured medium. fractutre1 Z is the rock physics model of the variable azimuth fracture corresponding to the first fracture azimuth angle; fractutre2 The rock physics model of the variable azimuth fracture corresponding to the second fracture azimuth angle.

[0016] Preferably, the step of performing anisotropic wave equation forward modeling based on the elastic coefficient matrix of the fractured medium to obtain common imaging point angle gather data at different azimuth angles includes:

[0017] Obtain the elastic wave equation; wherein the elastic wave equation reflects the relationship between the first-order stress and the elastic wave velocity in the cracked anisotropic medium.

[0018] The elastic wave equation is solved using the finite difference method to simulate the elastic wave field and obtain common imaging point angle gather data at different azimuth angles.

[0019] Preferably, the step of performing P-wave AVO analysis on the common imaging point corner gather data at different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data at different azimuth angles includes:

[0020] Preprocessing is performed on the common imaging point corner gather data under different azimuth angles to obtain the preprocessed CDP data under different azimuth angles;

[0021] Based on the preprocessed CDP data at different azimuth angles, the gradient and intercept of the AVO curve at different azimuth angles are obtained.

[0022] The gradients and intercepts of the AVO curves at different azimuth angles are subjected to intersection analysis, and a first straight line is obtained by fitting.

[0023] Based on the first straight line, obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element at different azimuth angles.

[0024] Preferably, the preprocessing of the common imaging point angle gather data at different azimuth angles to obtain preprocessed CDP data at different azimuth angles includes:

[0025] Bad path removal processing is performed on the common imaging point corner gather data under different azimuth angles to obtain valid CDP data;

[0026] The incident angle range of each CDP element in the valid CDP data is adjusted so that the incident angle value of each CDP element is the same, thereby obtaining preprocessed CDP data under different azimuth angles.

[0027] Preferably, obtaining the gradient and intercept of the AVO curve at different azimuth angles based on the preprocessed CDP data at different azimuth angles includes:

[0028] For the preprocessed CDP data at each of the different azimuth angles, perform the following operations to obtain the gradient and intercept of the AVO curve at each of the different azimuth angles:

[0029] Based on the preprocessed CDP data at this azimuth angle, the AVO curve at this azimuth angle is obtained;

[0030] The AVO curve at this azimuth angle is transformed into a second straight line; where the second straight line reflects the relationship between the P-wave amplitude and the square of the sine of the incident angle.

[0031] The gradient and intercept of the second straight line are extracted as the gradient and intercept of the AVO curve at that azimuth angle.

[0032] Preferably, predicting the development degree and orientation of cracks based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element includes:

[0033] Based on the magnitude of the correlation coefficient corresponding to each CDP element, the crack development level of that CDP element is obtained.

[0034] The most negative gradient direction corresponding to each CDP surface element is obtained as the crack development direction of that CDP surface element.

[0035] Secondly, embodiments of the present invention provide an apparatus for predicting cracks based on seismic wavefield forward modeling, the apparatus comprising:

[0036] The parameter acquisition unit is used to obtain the elastic coefficient matrix of the fracture medium based on a pre-established variable orientation fracture rock physics model.

[0037] The forward modeling unit is used to perform forward modeling of the anisotropic wave equation based on the elastic coefficient matrix of the fractured medium to obtain common imaging point corner gather data at different azimuth angles.

[0038] AVO analysis unit is used to perform P-wave AVO analysis on the common imaging point corner gather data under different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data under different azimuth angles.

[0039] The prediction unit is used to predict the development degree and orientation of cracks based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element.

[0040] Thirdly, embodiments of the present invention provide a storage medium storing program code, which, when executed by a processor, implements the method for predicting cracks based on seismic wavefield forward modeling as described in any of the above embodiments.

[0041] Fourthly, embodiments of the present invention provide an electronic device, the electronic device including a memory and a processor, the memory storing program code executable on the processor, the program code being executed by the processor to implement the method for predicting cracks based on seismic wavefield forward modeling as described in any of the above embodiments.

[0042] The method, apparatus, storage medium, and electronic device for predicting fractures based on seismic wavefield forward modeling provided in this invention obtain the elastic coefficient matrix of the fracture medium based on a variable azimuth fracture rock physics model, and then perform anisotropic wave equation forward modeling based on this matrix to obtain common imaging point angle gather data at different azimuth angles. This means that the embodiments of this invention fully consider the influence of fracture azimuth angle factors, thus better reflecting the actual fracture conditions in the work area and making the fracture prediction results more accurate. Simultaneously, the development degree and orientation of fractures are predicted based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, making the characterization of fracture characteristics quantitative and thus making the prediction process more convenient. Therefore, the technical solution provided in this invention can predict fractures more conveniently and accurately compared to existing technologies. Attached Figure Description

[0043] The scope of this invention can be better understood by reading the following detailed description of exemplary embodiments in conjunction with the accompanying drawings. The accompanying drawings are:

[0044] Figure 1 The method flow of this invention embodiment Figure 1 ;

[0045] Figure 2 The method flow of this invention embodiment Figure 2 ;

[0046] Figure 3 This is a schematic diagram of the common imaging point angle gather data with an azimuth angle of 0 degrees obtained by elastic wave forward modeling in an embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of the first straight line obtained by performing intersection analysis on the gradient and intercept of the AVO curves at different azimuth angles in an embodiment of the present invention.

[0048] Figure 5 This is a cross-sectional view of crack development in a portion of the CDP surface elements in the actual work area of ​​this invention embodiment;

[0049] Figure 6 This is a slice diagram and orientation diagram of the crack development degree of some CDP surface elements in the actual work area in this embodiment of the invention;

[0050] Figure 7 This is a structural diagram of the device according to an embodiment of the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the present invention clearer, the implementation method of the present invention will be described in detail below with reference to the accompanying drawings and embodiments, so that the process of how the present invention uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0052] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0053] Example 1

[0054] Currently, most research on fracture theory models is limited to single-fracture cases, with limited research on oblique fractures, which fails to reflect the actual geological conditions of real-world work areas. To improve the accuracy of fracture and fluid prediction, make fracture theory models more consistent with real fractured reservoir conditions, and enhance the quality and efficiency of seismic forward and inversion models, this invention is proposed. Because the fracture conditions described in this invention are highly consistent with actual fracture conditions in the work area, the forward modeling method can accurately predict the fracture density parameters of the work area, laying a solid foundation for subsequent seismic inversion. Fractures serve as both reservoir spaces for oil and gas and channels for their migration; areas with well-developed fractures often have abundant oil and gas resources. Based on the fracture development degree and orientation indications of this invention, the accuracy of oil and gas prediction can be significantly improved. Therefore, this invention has promising applications in fluid prediction and fracture fluid inversion in fractured reservoirs.

[0055] This invention specifically relates to the establishment of theoretical models for oblique fractures at different azimuth angles, the derivation and application of forward modeling equations for anisotropic media, and model verification. This invention can be used for forward modeling studies under geological conditions of intersecting fractures to study the variation law of the back-transmission coefficient under different azimuth angles.

[0056] According to embodiments of the present invention, a method for predicting cracks based on seismic wavefield forward modeling is provided, such as... Figure 1 As shown, the method described in this embodiment includes:

[0057] Step S101: Based on the pre-established rock physics model of variable orientation fracture, obtain the elastic coefficient matrix of the fracture medium.

[0058] In this embodiment, the rock physical model of the variable orientation fracture is expressed by the following expression:

[0059]

[0060] Among them, Z N Z represents the normal compliance of the crack. T θ represents the tangential compliance of the fracture; θ represents the fracture azimuth angle; and Z represents the rock physics model of the variable azimuth fracture.

[0061] Among them, the crack normal compliance Z N and crack tangential compliance Z T This can be expressed as a calculation expression for the fracture medium and fracture density:

[0062]

[0063]

[0064] In the above formula, λ is the first Lamé constant of the fractured medium, μ is the second Lamé constant of the fractured medium, and e is the fracture density.

[0065] In this embodiment, the elastic coefficient matrix of the fractured medium is obtained using the following expression:

[0066] C eff =(M background +Z fractutre1 +Z fractutre2 ) -1

[0067] Among them, C eff M is the elastic coefficient matrix of the fractured medium; background Z represents the compliance coefficient matrix of the fractured medium. fractutre1 Z is the rock physics model of the variable azimuth fracture corresponding to the first fracture azimuth angle; fractutre2 The rock physics model of the variable azimuth fracture corresponding to the second fracture azimuth angle.

[0068] Step S102: Perform forward modeling of the anisotropic wave equation based on the elastic coefficient matrix of the fractured medium to obtain common imaging point corner gather data at different azimuth angles;

[0069] For anisotropic media, Ruger presented the reflection P-wave coefficient of the incident plane P-wave under the assumptions of small changes in elastic parameters and weak anisotropy on both sides of the interface, where the HTI / HTI interfaces have the same anisotropic symmetry axis at the top and bottom. However, this method can only handle orthogonal cracks and is not applicable to the crack development conditions in actual work areas. Considering this situation, this embodiment adopts forward modeling of the anisotropic wave equation. The wave equation can handle complex crack development conditions and is not limited to the case of orthogonal cracks.

[0070] In this embodiment, the step of performing forward modeling of the anisotropic wave equation based on the elastic coefficient matrix of the fractured medium to obtain common imaging point angle gather data at different azimuth angles includes:

[0071] Obtain the elastic wave equation; wherein the elastic wave equation reflects the relationship between the first-order stress and the elastic wave velocity in the cracked anisotropic medium.

[0072] The elastic wave equation is solved using the finite difference method to simulate the elastic wave field and obtain common imaging point angle gather data at different azimuth angles.

[0073] Specifically, firstly, since the rock physics model of the variable orientation fracture is an anisotropic medium, for anisotropic media, the relationship between strain e and displacement u is:

[0074]

[0075]

[0076] In anisotropic media, the elastic coefficient tensor is spatially oriented, and the stress-strain relationship is very complex, usually represented by an elastic coefficient matrix. According to Hooke's law, the relationship between stress σ and strain e in common anisotropic media can be expressed as:

[0077]

[0078] set up Therefore, the equations of motion in an anisotropic medium are:

[0079]

[0080] Where, the displacement vector u = (u x ,u y ,u z ) T External force vector f = (f x ,f y ,f z ) T Let v = (v x ,v y ,v z ) T Let represent the velocity vector. Therefore, combining the above formulas yields the elastic wave equation, which reflects the relationship between the first-order stress and the elastic wave velocity in an anisotropic medium with cracks:

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] Where ρ is the crack density, σ xx Let σ be the first-order stress in the x-direction. yx For the first-order stress in the yx direction, σ zy The first-order stress is in the zy direction; v x Let v be the elastic wave velocity in the x-direction. y Let v be the elastic wave velocity in the y-direction. z C represents the elastic wave velocity in the z-direction; 11 C 12 C 13 C 21 C 22 C 23 C 31 C 32 C 33 C 44 C 55 C 66 All are constants.

[0089] Then, the finite difference method is used to solve the above elastic wave equation. The staggered mesh high-order difference method, compared with the regular mesh high-order difference method, can further improve the accuracy of the numerical simulation and suppress numerical dispersion. A high-order difference approximation is performed on the first-order stress-velocity equation. The following is a high-order finite difference scheme with 2L-order spatial difference accuracy and second-order time difference accuracy:

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] in:

[0100]

[0101]

[0102] These represent the forward and backward differences, respectively, where x i (i = 1, 2, 3) represent x, y, z respectively; Δx, Δz represent the grid spacing in the x and z directions respectively; Δt represents the time step; express The same applies to the others.

[0103] By solving the elastic wave equation using the finite difference method, i.e. simulating the elastic wave field, we can obtain common imaging point angle gather data at different azimuth angles.

[0104] Step S103: Perform P-wave AVO analysis on the common imaging point corner gather data under different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data under different azimuth angles.

[0105] In this embodiment, performing P-wave AVO analysis on the common imaging point corner gather data at different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data at different azimuth angles includes:

[0106] The common imaging point corner gather data at different azimuth angles are preprocessed to obtain preprocessed CDP data at different azimuth angles; based on the preprocessed CDP data at different azimuth angles, the gradient and intercept of the AVO curve at different azimuth angles are obtained; the gradient and intercept of the AVO curve at different azimuth angles are subjected to intersection analysis to obtain a first straight line; based on the first straight line, the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element at different azimuth angles are obtained.

[0107] In this embodiment, the preprocessing of the common imaging point angle gather data under different azimuth angles to obtain preprocessed CDP data under different azimuth angles includes: performing bad channel removal processing on the common imaging point angle gather data under different azimuth angles to obtain valid CDP data; adjusting the incident angle range of each CDP element in the valid CDP data so that the incident angle value of each CDP element is the same, thereby obtaining preprocessed CDP data under different azimuth angles.

[0108] In this embodiment, obtaining the gradient and intercept of the AVO curve at different azimuth angles based on the preprocessed CDP data at different azimuth angles includes:

[0109] For the preprocessed CDP data at each azimuth angle, perform the following operations to obtain the gradient and intercept of the AVO curve at each azimuth angle: Based on the preprocessed CDP data at that azimuth angle, obtain the AVO curve at that azimuth angle; transform the AVO curve at that azimuth angle into a second straight line; wherein, the second straight line reflects the relationship between the P-wave amplitude value and the square of the sine of the incident angle; extract the gradient and intercept of the second straight line as the gradient and intercept of the AVO curve at that azimuth angle.

[0110] Specifically, for the common imaging point corner gather data obtained in step S102 under different azimuth angles, preprocessing is first performed. The preprocessing includes removing bad channels from the common imaging point corner gather data under different azimuth angles and adjusting the incident angle of each CDP element to be the same to facilitate the subsequent extraction of gradient and intercept.

[0111] Then, a certain angular range is selected as the azimuth surface element, and the amplitude value changes with the incident angle for the seismic data under each azimuth angle (i.e., the above AVO curve). Since the AVO curve is not a straight line, it is not conducive to the extraction of gradient and intercept. Therefore, the curve of amplitude value changing with incident angle is changed to the curve of amplitude value changing with the square of the sine of incident angle. The modified AVO curve becomes a straight line, and then the gradient and intercept of the straight line are extracted to obtain the gradient and intercept of the AVO curve.

[0112] An intersection analysis was performed on the extracted AVO intercept and gradient data volumes at different azimuth angles to obtain a straight line, as shown above. Figure 4 As shown, this straight line also provides the linearity between the AVO intercept and gradient at different azimuth angles, i.e., the correlation coefficient (R²). 2 , Figure 4 The correlation coefficient is 0.8631 and the azimuth angle corresponding to the most negative gradient. Figure 4 The azimuth angle corresponding to the most negative gradient is 30 degrees.

[0113] This embodiment addresses the impact of fracture anisotropy on AVO analysis by employing azimuth AVO analysis technology based on P-wave azimuth anisotropy analysis to mitigate the influence of fracture anisotropy on AVO hydrocarbon analysis.

[0114] Step S104: Based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, predict the development degree and orientation of the crack.

[0115] In this embodiment, predicting the development degree and orientation of cracks based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element includes:

[0116] Based on the magnitude of the correlation coefficient corresponding to each CDP surface element, the crack development level of the CDP surface element is obtained; the most negative gradient direction corresponding to each CDP surface element is obtained as the crack development direction of the CDP surface element.

[0117] The theoretical basis for this embodiment to predict the development degree and orientation of cracks based on the correlation coefficient and the most negative gradient direction corresponding to each CDP element is as follows:

[0118] Based on the oblique double-fracture petrophysical model, five single-fracture groups with different fracture densities developed in the direction of 45 degrees north by east were established. Seismic gathers at different azimuth angles were obtained by wavefield simulation. AVO analysis was performed on the seismic gathers at different azimuth angles to study the relationship between the intercept, gradient, fracture direction, and development degree at different azimuth angles.

[0119] Through AVO analysis of five single-group fracture models with different fracture densities, the squared correlation coefficient R between fracture density, gradient, and intercept was determined. 2 It exhibits an approximately linear relationship, R 2 The larger the value, the greater the crack density, indicating that crack density is related to R. 2 It's a direct proportional relationship; for real-world data, you can use R. 2 This parameter characterizes the degree of fracture development. Furthermore, the direction of fracture development can be characterized by the azimuth angle corresponding to the most negative gradient; the direction of the most negative gradient is the fracture's strike direction, and vice versa. This theory can also be used in dual-set fracture models to identify the degree and direction of fracture development, and oil and gas exploration can be based on these theoretical results.

[0120] The method for predicting fractures based on seismic wavefield forward modeling provided in this invention obtains the elastic coefficient matrix of the fracture medium based on a variable azimuth fracture rock physics model, and then performs anisotropic wave equation forward modeling based on this matrix to obtain common imaging point angle gather data at different azimuth angles. This means that the method fully considers the influence of fracture azimuth angle factors, thus better reflecting the actual fracture conditions in the work area and making the fracture prediction results more accurate. Furthermore, the method predicts the development degree and orientation of fractures based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, making the characterization of fracture characteristics quantitative and thus facilitating the prediction process. Therefore, the technical solution provided in this invention can predict fractures more conveniently and accurately compared to existing technologies.

[0121] Example 2

[0122] This embodiment uses an actual fracture prediction process as an example to further explain in detail the method of predicting fractures based on seismic wavefield forward modeling. The experimental data in this case are well logging data from a certain layer in a certain work area in western China, with a downward 30ms time, including 51 X-line seismic interpretation profiles for connecting lines and 51 Inline seismic interpretation profiles for main logging lines, with a total of 81,199 seismic traces.

[0123] like Figure 2 As shown, the method described in this embodiment includes:

[0124] Step S201: Based on the pre-established rock physics model of variable orientation fracture, obtain the elastic coefficient matrix of the fracture medium.

[0125] Specifically, based on the logging data and fracture orientation information of the actual work area, the established variable orientation oblique fracture theoretical model is input, and then the fracture medium elastic coefficient matrix obtained by the model is used for anisotropic forward modeling.

[0126] In this embodiment, the rock physical model of the variable orientation fracture is expressed by the following expression:

[0127]

[0128] Among them, Z N Z represents the normal compliance of the crack. T θ represents the tangential compliance of the fracture; θ represents the fracture azimuth angle; and Z represents the rock physics model of the variable azimuth fracture.

[0129] In this embodiment, the elastic coefficient matrix of the fractured medium is obtained using the following expression:

[0130] C eff =(M background +Z fractutre1 +Z fractutre2 ) -1

[0131] Among them, C eff M is the elastic coefficient matrix of the fractured medium; background Z represents the compliance coefficient matrix of the fractured medium. fractutre1 Z is the rock physics model of the variable azimuth fracture corresponding to the first fracture azimuth angle; fractutre2 The rock physics model of the variable azimuth fracture corresponding to the second fracture azimuth angle.

[0132] Step S202: Perform forward modeling of the anisotropic wave equation based on the elastic coefficient matrix of the fractured medium to obtain common imaging point corner gather data at different azimuth angles;

[0133] In this embodiment, the step of performing forward modeling of the anisotropic wave equation based on the elastic coefficient matrix of the fractured medium to obtain common imaging point angle gather data at different azimuth angles includes:

[0134] The elastic wave equation is obtained; wherein the elastic wave equation reflects the relationship between the first-order stress and the elastic wave velocity in the anisotropic medium with cracks; the elastic wave equation is solved by the finite difference method to simulate the elastic wave field and obtain the common imaging point angle gather data at different azimuth angles.

[0135] The above method allows the acquisition of 2601 CDP surface data points from the aforementioned 81199 seismic traces. A schematic diagram of the common imaging point angle gather data with an azimuth angle of 0 degrees obtained through elastic wave forward modeling is shown below. Figure 3 As shown.

[0136] Step S203: Preprocess the common imaging point corner gather data under different azimuth angles to obtain preprocessed CDP data under different azimuth angles.

[0137] In this embodiment, the preprocessing specifically includes: performing bad channel removal processing on the common imaging point corner gather data under different azimuth angles to obtain valid CDP data; adjusting the incident angle range of each CDP element in the valid CDP data so that the incident angle value of each CDP element is the same, thereby obtaining the preprocessed CDP data under different azimuth angles.

[0138] Step S204: Based on the preprocessed CDP data at different azimuth angles, obtain the gradient and intercept of the AVO curve at different azimuth angles;

[0139] In this embodiment, obtaining the gradient and intercept of the AVO curve at different azimuth angles based on the preprocessed CDP data at different azimuth angles includes:

[0140] For the preprocessed CDP data at each of the different azimuth angles, perform the following operations to obtain the gradient and intercept of the AVO curve at each of the different azimuth angles:

[0141] Based on the preprocessed CDP data at this azimuth angle, the AVO curve at this azimuth angle is obtained; the AVO curve at this azimuth angle is transformed into a second straight line; wherein, the second straight line reflects the relationship between the P-wave amplitude value and the square of the sine of the incident angle; the gradient and intercept of the second straight line are extracted as the gradient and intercept of the AVO curve at this azimuth angle.

[0142] Step S205: Perform intersection analysis on the gradient and intercept of the AVO curves under different azimuth angles, and fit to obtain the first straight line;

[0143] The first straight line obtained in this embodiment is as follows: Figure 4 As shown.

[0144] Step S206: Based on the first straight line, obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element at different azimuth angles;

[0145] The first straight line obtained through step S205 can provide the linearity between the AVO intercept and gradient at different azimuth angles, i.e., the correlation coefficient (R²). Figure 4 The correlation coefficient is 0.8631 and the azimuth angle corresponding to the most negative gradient. Figure 4 The azimuth angle corresponding to the most negative gradient is 30 degrees.

[0146] Since there are a total of 2601 CDP surface data elements, a total of 2601 correlation coefficients and 2601 most negative gradient directions can be obtained.

[0147] Step S207: Based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, predict the development degree and orientation of the crack.

[0148] In this embodiment, predicting the development degree and orientation of cracks based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element includes:

[0149] Based on the magnitude of the correlation coefficient corresponding to each CDP surface element, the crack development level of the CDP surface element is obtained; the most negative gradient direction corresponding to each CDP surface element is obtained as the crack development direction of the CDP surface element.

[0150] Specifically, the extracted correlation coefficients are displayed using a color graph, such as... Figure 5 As shown, the darker the color, the higher the value of the correlation coefficient. A higher correlation coefficient indicates a higher degree of crack development in the CDP element, meaning better crack development. Conversely, a lower correlation coefficient indicates a lower degree of crack development in the CDP element. Figure 5 The white area in the middle indicates that the crack is not developed.

[0151] The direction of crack development is represented by arrows pointing in different directions, such as... Figure 6 As shown, the output of step S207 is a slice diagram showing the degree of crack development and crack orientation. Figure 6 As can be seen, in areas where cracks develop, the cracks tend to gravitate towards 30 degrees and 150 degrees. The cracks in the work area tested this time developed at 30 degrees east of north and 30 degrees west of north (150 degrees), indicating that the results obtained using the method described in this embodiment are in good agreement with the actual results. The experiment demonstrates that the technical solution provided by this invention can be used to obtain the degree and direction of crack development in actual work areas.

[0152] The method for predicting fractures based on seismic wavefield forward modeling provided in this invention obtains the elastic coefficient matrix of the fracture medium based on a variable azimuth fracture rock physics model, and then performs anisotropic wave equation forward modeling based on this matrix to obtain common imaging point angle gather data at different azimuth angles. This means that the method fully considers the influence of fracture azimuth angle factors, thus better reflecting the actual fracture conditions in the work area and making the fracture prediction results more accurate. Furthermore, the method predicts the development degree and orientation of fractures based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, making the characterization of fracture characteristics quantitative and thus facilitating the prediction process. Therefore, the technical solution provided in this invention can predict fractures more conveniently and accurately compared to existing technologies.

[0153] Example 3

[0154] Corresponding to the above-described method embodiments, the present invention also provides an apparatus for predicting cracks based on seismic wavefield forward modeling, such as... Figure 7 As shown, the device includes:

[0155] The parameter acquisition unit 301 is used to obtain the elastic coefficient matrix of the fracture medium based on a pre-established variable orientation fracture rock physical model.

[0156] Forward modeling unit 302 is used to perform forward modeling of anisotropic wave equations based on the elastic coefficient matrix of the fractured medium to obtain common imaging point corner gather data at different azimuth angles;

[0157] AVO analysis unit 303 is used to perform P-wave AVO analysis on the common imaging point corner gather data under different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data under different azimuth angles.

[0158] The prediction unit 304 is used to predict the development degree and orientation of cracks based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element.

[0159] In this embodiment, the rock physical model of the variable orientation fracture is expressed by the following expression:

[0160]

[0161] Among them, Z N Z represents the normal compliance of the crack. T θ represents the tangential compliance of the fracture; θ represents the fracture azimuth angle; and Z represents the rock physics model of the variable azimuth fracture.

[0162] In this embodiment, the parameter acquisition unit 301 obtains the elastic coefficient matrix of the fractured medium using the following expression:

[0163] C eff =(M background +Z fractutre1 +Z fractutre2 ) -1

[0164] Among them, C eff M is the elastic coefficient matrix of the fractured medium; background Z represents the compliance coefficient matrix of the fractured medium. fractutre1 Z is the rock physics model of the variable azimuth fracture corresponding to the first fracture azimuth angle; fractutre2 The rock physics model of the variable azimuth fracture corresponding to the second fracture azimuth angle.

[0165] In this embodiment, the forward modeling unit 302 includes:

[0166] The wave equation acquisition unit is used to acquire the elastic wave equation; wherein, the elastic wave equation reflects the relationship between the first-order stress and the elastic wave velocity in the cracked anisotropic medium.

[0167] The simulation unit is used to solve the elastic wave equation using the finite difference method to simulate the elastic wave field and obtain common imaging point angle gather data at different azimuth angles.

[0168] In this embodiment, the AVO analysis unit 303 includes:

[0169] The preprocessing unit is used to preprocess the common imaging point corner gather data under different azimuth angles to obtain the preprocessed CDP data under different azimuth angles.

[0170] The AVO curve parameter acquisition unit is used to obtain the gradient and intercept of the AVO curve at different azimuth angles based on the preprocessed CDP data at different azimuth angles.

[0171] The intersection analysis unit is used to perform intersection analysis on the gradient and intercept of the AVO curves under different azimuth angles, and fit to obtain the first straight line;

[0172] The correlation coefficient and the most negative gradient direction acquisition unit is used to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element at different azimuth angles based on the first straight line.

[0173] In this embodiment, the preprocessing unit includes:

[0174] The bad sector removal unit is used to perform bad sector removal processing on the common imaging point corner gather data under different azimuth angles to obtain valid CDP data.

[0175] An incident angle adjustment unit is used to adjust the incident angle range of each CDP surface element in the effective CDP data so that the incident angle value of each CDP surface element is the same, thereby obtaining preprocessed CDP data under different azimuth angles.

[0176] In this embodiment, the AVO curve parameter acquisition unit obtains the gradient and intercept of the AVO curve at different azimuth angles using the following method:

[0177] For the preprocessed CDP data at each of the different azimuth angles, perform the following operations to obtain the gradient and intercept of the AVO curve at each of the different azimuth angles:

[0178] Based on the preprocessed CDP data at this azimuth angle, the AVO curve at this azimuth angle is obtained;

[0179] The AVO curve at this azimuth angle is transformed into a second straight line; where the second straight line reflects the relationship between the P-wave amplitude and the square of the sine of the incident angle.

[0180] The gradient and intercept of the second straight line are extracted as the gradient and intercept of the AVO curve at that azimuth angle.

[0181] In this embodiment, the prediction unit 304 predicts the development degree and orientation of cracks in the following manner:

[0182] Based on the magnitude of the correlation coefficient corresponding to each CDP element, the crack development level of that CDP element is obtained.

[0183] The most negative gradient direction corresponding to each CDP surface element is obtained as the crack development direction of that CDP surface element.

[0184] For details regarding the working principle, workflow, and specific implementation methods of the aforementioned device, please refer to the specific implementation methods of the method for predicting cracks based on seismic wavefield forward modeling provided by this invention. The same technical content will not be described in detail here.

[0185] The device for predicting fractures based on seismic wavefield forward modeling provided in this invention obtains the elastic coefficient matrix of the fracture medium based on a variable azimuth fracture rock physics model, and performs anisotropic wave equation forward modeling based on this matrix to obtain common imaging point angle gather data at different azimuth angles. This invention fully considers the influence of fracture azimuth angle factors, thus better reflecting the actual fracture conditions in the work area and making the fracture prediction results more accurate. Simultaneously, it predicts the development degree and orientation of fractures based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, making the characterization of fracture characteristics quantitative and thus facilitating the prediction process. Therefore, the technical solution provided in this invention can predict fractures more conveniently and accurately compared to existing technologies.

[0186] Example 4

[0187] According to an embodiment of the present invention, a storage medium is also provided, wherein program code is stored on the storage medium, and when the program code is executed by a processor, the method for predicting cracks based on seismic wavefield forward modeling as described in any of the above embodiments is implemented.

[0188] Example 5

[0189] According to an embodiment of the present invention, an electronic device is also provided, the electronic device including a memory and a processor, wherein the memory stores program code that can run on the processor, and when the program code is executed by the processor, it implements the method for predicting cracks based on seismic wavefield forward modeling as described in any of the above embodiments.

[0190] The method, apparatus, storage medium, and electronic device for predicting fractures based on seismic wavefield forward modeling provided in this invention, obtain the elastic coefficient matrix of the fracture medium based on a variable azimuth fracture rock physics model, and then perform anisotropic wave equation forward modeling based on this matrix to obtain common imaging point angle gather data at different azimuth angles. This invention fully considers the influence of fracture azimuth angle factors, thus better reflecting the actual fracture conditions in the work area and making the fracture prediction results more accurate. Simultaneously, the development degree and orientation of fractures are predicted based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, making the characterization of fracture characteristics quantitative and thus facilitating the prediction process. Therefore, the technical solution provided in this invention can predict fractures more conveniently and accurately compared to existing technologies.

[0191] This invention presents a modeling method for variable-azimuth oblique cracks based on the coin-shaped crack assumption. Following forward modeling, P-wave AVO analysis is performed, which can effectively predict crack density information, significantly improving the accuracy of crack prediction. This invention shows great promise in terms of cost savings and improved quality of processing results.

[0192] This invention addresses the difficulties in forward modeling and the low prediction accuracy of intersecting fractures in actual geological conditions. Based on well logging data and fracture orientation information from the actual work area, a theoretical model of variable-azimuth oblique fractures is established. Then, the obtained fracture medium elastic coefficient matrix is ​​used to perform forward modeling of the anisotropic wave equation. The forward modeling results are then used for P-wave AVO analysis to predict fracture density information in the actual work area, yielding more accurate fracture density information than previous methods. Fractures serve as both reservoirs and channels for oil and gas migration; areas with well-developed fractures often have abundant oil and gas resources. The fracture development degree and orientation indication of this invention can significantly improve the accuracy of oil and gas prediction. Therefore, this invention has promising applications in fluid prediction of fractured reservoirs and fracture fluid inversion.

[0193] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed.

[0194] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of the embodiments of the present invention, depending on actual needs.

[0195] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0196] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause an electronic device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0197] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of protection of this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for predicting cracks based on seismic wavefield forward modeling, characterized in that, The method includes: Based on a pre-established rock physics model of variable orientation fractures, the elastic coefficient matrix of the fracture medium is obtained. Anisotropic wave equation forward modeling is performed based on the elastic coefficient matrix of the fractured medium to obtain common imaging point corner gather data at different azimuth angles; P-wave AVO analysis was performed on the common imaging point corner gather data under different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data under different azimuth angles. Based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element, the development degree and orientation of the crack are predicted. The step of performing P-wave AVO analysis on the common imaging point corner gather data at different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data at different azimuth angles includes: Preprocessing is performed on the common imaging point corner gather data under different azimuth angles to obtain the preprocessed CDP data under different azimuth angles; Based on the preprocessed CDP data at different azimuth angles, the gradient and intercept of the AVO curve at different azimuth angles are obtained. The gradients and intercepts of the AVO curves at different azimuth angles are subjected to intersection analysis, and a first straight line is obtained by fitting. Based on the first straight line, obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element at different azimuth angles; The process of obtaining the gradient and intercept of the AVO curve at different azimuth angles based on the preprocessed CDP data at these different azimuth angles includes: For the preprocessed CDP data at each of the different azimuth angles, perform the following operations to obtain the gradient and intercept of the AVO curve at each of the different azimuth angles: Based on the preprocessed CDP data at this azimuth angle, the AVO curve at this azimuth angle is obtained; The AVO curve at this azimuth angle is transformed into a second straight line; where the second straight line reflects the relationship between the P-wave amplitude and the square of the sine of the incident angle. Extract the gradient and intercept of the second straight line as the gradient and intercept of the AVO curve at that azimuth angle; The prediction of crack development degree and orientation based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element includes: Based on the magnitude of the correlation coefficient corresponding to each CDP element, the crack development level of that CDP element is obtained. The most negative gradient direction corresponding to each CDP surface element is obtained as the crack development direction of that CDP surface element.

2. The method for predicting cracks based on seismic wavefield forward modeling according to claim 1, characterized in that, The rock physics model of the variable orientation fracture is expressed by the following expression: Where ZN is the normal compliance of the fracture; ZT is the tangential compliance of the fracture; θ is the azimuth angle of the fracture; and Z is the rock physics model of the variable azimuth fracture.

3. The method for predicting cracks based on seismic wavefield forward modeling according to claim 2, characterized in that, The elastic coefficient matrix of the fractured medium is obtained using the following expression: in, The elastic coefficient matrix of the fractured medium; This represents the compliance coefficient matrix of the fractured medium. The rock physics model of the variable azimuth fracture corresponding to the first fracture azimuth angle; The rock physics model of the variable azimuth fracture corresponding to the second fracture azimuth angle.

4. The method for predicting cracks based on seismic wavefield forward modeling according to claim 1, characterized in that, The process of performing forward modeling of the anisotropic wave equation based on the elastic coefficient matrix of the fractured medium to obtain common imaging point angle gather data at different azimuth angles includes: Obtain the elastic wave equation; wherein the elastic wave equation reflects the relationship between the first-order stress and the elastic wave velocity in the cracked anisotropic medium. The elastic wave equation is solved using the finite difference method to simulate the elastic wave field and obtain common imaging point angle gather data at different azimuth angles.

5. The method for predicting cracks based on seismic wavefield forward modeling according to claim 1, characterized in that, The preprocessing of the common imaging point corner gather data at different azimuth angles to obtain preprocessed CDP data at different azimuth angles includes: Bad path removal processing is performed on the common imaging point corner gather data under different azimuth angles to obtain valid CDP data; The incident angle range of each CDP element in the valid CDP data is adjusted so that the incident angle value of each CDP element is the same, thereby obtaining preprocessed CDP data under different azimuth angles.

6. A device for predicting cracks based on seismic wavefield forward modeling, characterized in that, The device includes: The parameter acquisition unit is used to obtain the elastic coefficient matrix of the fracture medium based on a pre-established variable orientation fracture rock physics model. The forward modeling unit is used to perform forward modeling of the anisotropic wave equation based on the elastic coefficient matrix of the fractured medium to obtain common imaging point corner gather data at different azimuth angles. AVO analysis unit is used to perform P-wave AVO analysis on the common imaging point corner gather data under different azimuth angles to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element in the common imaging point corner gather data under different azimuth angles. The prediction unit is used to predict the development degree and orientation of cracks based on the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element. The AVO analysis unit includes: The preprocessing unit is used to preprocess the common imaging point corner gather data under different azimuth angles to obtain the preprocessed CDP data under different azimuth angles. The AVO curve parameter acquisition unit is used to obtain the gradient and intercept of the AVO curve at different azimuth angles based on the preprocessed CDP data at different azimuth angles. The intersection analysis unit is used to perform intersection analysis on the gradient and intercept of the AVO curves under different azimuth angles, and fit to obtain the first straight line; The correlation coefficient and the most negative gradient direction acquisition unit is used to obtain the correlation coefficient and the most negative gradient direction corresponding to each CDP surface element under different azimuth angles based on the first straight line; The AVO curve parameter acquisition unit is used for: For the preprocessed CDP data at each of the different azimuth angles, perform the following operations to obtain the gradient and intercept of the AVO curve at each of the different azimuth angles: Based on the preprocessed CDP data at this azimuth angle, the AVO curve at this azimuth angle is obtained; The AVO curve at this azimuth angle is transformed into a second straight line; where the second straight line reflects the relationship between the P-wave amplitude and the square of the sine of the incident angle. Extract the gradient and intercept of the second straight line as the gradient and intercept of the AVO curve at that azimuth angle; The prediction unit is used for: Based on the magnitude of the correlation coefficient corresponding to each CDP element, the crack development level of that CDP element is obtained. The most negative gradient direction corresponding to each CDP surface element is obtained as the crack development direction of that CDP surface element.

7. A storage medium storing program code, characterized in that, When the program code is executed by the processor, it implements the method for predicting cracks based on seismic wavefield forward modeling as described in any one of claims 1 to 5.

8. An electronic device, characterized in that, The electronic device includes a memory and a processor. The memory stores program code that can run on the processor. When the program code is executed by the processor, it implements the method for predicting cracks based on seismic wavefield forward modeling as described in any one of claims 1 to 5.

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