Method for evaluating AVO feature preservation of pre-stack seismic gathers

Abstract

The present application relates to the technical field of geophysical prospecting, in particular to a pre-stack seismic data AVO feature preservation evaluation method, comprising the following steps: S1, obtaining a pre-stack seismic trace set, calculating the intercept P(t) and gradient G(t) of the pre-stack seismic trace set, wherein t is the time of obtaining the pre-stack seismic trace set; S2, calculating an artificial synthetic seismic trace set according to the intercept P(t) and gradient G(t); S3, calculating a consistency indicator of the pre-stack seismic trace set and the artificial synthetic seismic trace set; S4, the smaller the difference between the consistency indicator and a preset threshold value, the better the AVO feature preservation, and the larger the difference between the consistency indicator and the preset threshold value, the worse the AVO feature preservation. The quantitative evaluation result can directly reflect the preservation of the trace set AVO feature, improve the accuracy and work efficiency of the AVO feature preservation evaluation of the data, and help optimize the processing flow and parameters by comparing the change trend of the indicator before and after processing to determine the influence of the processing on the trace set AVO feature.

Description

Technical Field

[0001] The present invention relates to the field of geophysical exploration technology, and in particular to a method for evaluating the preservation of AVO characteristics of pre-stack seismic gathers. Background Art

[0002] The AVO attribute of prestack seismic data contains more information about the subsurface medium and can be used to invert the physical properties of the subsurface medium. It is one of the most important attributes of seismic data. In lithologic gas reservoirs, extracting the physical properties of the subsurface medium from AVO features through inversion techniques is a key basis for finding and optimizing oil and gas reservoirs.

[0003] Current methods for evaluating AVO preservation are mostly qualitative, such as the residual method: subtracting pre- and post-processing data to see if the residual contains valid signals; the along-amplitude analysis method: observing whether the trend of seismic wave energy in the marker layer with offset distance remains consistent before and after processing; and the wellside forward comparison method: using well logging data to create wellside synthetic gathers and comparing the AVO characteristics of the synthetic gathers with those of the seismic data to determine AVO preservation. These methods all have limitations in practice: the residual method and along-amplitude analysis method are only qualitative and unsuitable for evaluating AVO preservation before and after frequency-boosting processing such as deconvolution; the wellside forward comparison method requires well logging data within the work area and is only applicable to evaluating seismic gathers after migration. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiency in the prior art that whether the AVO characteristics of pre-stack seismic gathers are maintained during seismic data processing can only be qualitatively evaluated, and an evaluation method for the preservation of AVO characteristics of the gathers based on the seismic data itself is proposed.

[0005] A method for evaluating the preservation of AVO characteristics of pre-stack seismic gathers includes the following steps:

[0006] S1, obtaining a pre-stack seismic gather, and calculating the intercept P(t) and gradient G(t) of the pre-stack seismic gather, where t is the time when the pre-stack seismic gather is obtained;

[0007] S2, calculating an artificial synthetic seismic gather according to the intercept P(t) and the gradient G(t);

[0008] S3, calculating the consistency indicator factor of the pre-stack seismic gather and the synthetic seismic gather;

[0009] S4, judging the maintainability of the AVO feature according to the difference between the consistency indicator factor and a preset threshold.

[0010] Furthermore, the consistency indicator factor in step S3 is calculated by the following formula:

[0011]

[0012] Wherein, a represents the pre-stack seismic gather, b represents the synthetic seismic gather, CC is the correlation coefficient, and DIS is the Euclidean distance.

[0013] Furthermore, the calculation formula of the Euclidean distance is:

[0014]

[0015] Among them, m is the starting time of the sampling window, n is the ending time of the sampling window, and a k is the pre-stack seismic gather at the kth sampling moment, b k is the artificially synthesized seismic gather at the kth sampling moment.

[0016] Furthermore, the calculation formula of the correlation coefficient is:

[0017]

[0018] Among them, m is the starting time of the sampling window, n is the ending time of the sampling window, and a k is the pre-stack seismic gather at the kth sampling moment, is the average value of the prestack seismic gathers within the sampling time window, b k is the artificial synthetic seismic gather at the kth sampling moment, It is the average value of the artificially synthesized seismic gathers within the sampling time window.

[0019] Furthermore, the calculation formula for the intercept P(t) and gradient G(t) of the pre-stack seismic gather in step S1 is the second-order Aki-Richards reflection coefficient formula.

[0020] Furthermore, step S1 also includes smoothing the intercept P(t) and gradient G(t) of the calculated pre-stack seismic gathers.

[0021] Furthermore, in step S2, the calculation formula for calculating the synthetic seismic gather according to the intercept P(t) and the gradient G(t) is the second-order Aki-Richards reflection coefficient formula.

[0022] Preferably, the step of obtaining pre-stack seismic data includes obtaining longitudinal wave seismic data through a detector, processing the longitudinal wave seismic data using a seismic wave longitudinal wave processing method, and obtaining an angle domain CDP data set with the dynamic correction removed after the dynamic correction tensile distortion.

[0023] Preferably, the angle domain CDP gather should contain more than 3 angles, and the differences between adjacent angles should be equal.

[0024] Based on the same inventive concept, a device for evaluating the preservation of AVO features of pre-stack seismic trace gathers is proposed, which is characterized in that it includes at least one processor and a memory communicatively connected to the at least one processor; wherein the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute any one of the methods described above.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention obtains the intercept and gradient attributes of the pre-stack seismic gather, and calculates the artificially synthesized seismic gather data based on the intercept and gradient attributes. The consistency indicator factor is calculated by combining the correlation coefficient and distance of the similarity between the actual seismic gather and the artificially synthesized gather. The consistency indicator factor is a quantitative value, and its value is between -2 and 1. The closer to 1, the more similar the two are and the amplitude values ​​are close. The smaller than 1, the more similar the two are and the amplitude values ​​are large. Therefore, the closer the indicator factor is to 1, the better the AVO feature preservation of the seismic data is, and the further away from 1, the worse the AVO feature preservation is. The quantitative evaluation result can directly and clearly reflect the preservation of the AVO feature of the gather, greatly improving the accuracy and work efficiency of the evaluation of the AVO feature preservation of the data during the seismic data processing process.

[0027] 2. It can also play a positive role in the seismic data processing process. It can evaluate the final result gather after the data processing is completed, and can also dynamically evaluate the gather data before and after a certain step or several steps in the data processing process. If the indicator factor becomes larger, it means that the processing step not only maintains the previous AVO characteristics, but also improves the gather quality. On the contrary, if the indicator factor becomes smaller, it means that the processing step destroys the original AVO characteristics. By comparing the changing trends of the indicator factor before and after processing, the impact of the processing step on the gather AVO characteristics can be judged, helping to optimize the processing process and processing parameters.

[0028] 3. The rate of change of the indicator factor is used to optimize the processing flow and reduce inefficient links. For example, the migrated data set usually needs some processing, such as residual time difference correction, energy balancing, denoising, etc. The degree of influence of these processing on the data set quality is reflected by the rate of change of the indicator factor. Steps with large change rates are retained, and steps with small change rates are eliminated. This not only ensures the quality of the data, but also further reduces the processing steps and improves the processing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of an evaluation method based on AVO feature preservation of seismic gathers;

[0030] Figure 2 The angle domain CDP gather map obtained in step S1 of Example 1;

[0031] Figure 3 This is the intercept profile obtained by the second-order Aki-Richards reflection coefficient formula in step S1 of Example 1;

[0032] Figure 4 The gradient profile obtained by the second-order Aki-Richards reflection coefficient formula in step S1 of Example 1;

[0033] Figure 5 The artificially synthesized seismic gather map obtained in step S2 of Example 1;

[0034] Figure 6 The IF plane diagram of the consistency indicator factor obtained in step S3 of Example 1. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with test examples and specific embodiments. However, this should not be understood as limiting the scope of the present invention to the following embodiments, and all technologies implemented based on the present invention fall within the scope of the present invention.

[0036] Example 1

[0037] This embodiment provides a method for evaluating the preservation of AVO characteristics of a gather based on the quantitative evaluation of seismic data itself, comprising the following steps:

[0038] S1, obtaining a pre-stack seismic gather, and calculating the intercept P(t) and gradient G(t) of the pre-stack seismic gather, where t is the time when the pre-stack seismic gather is obtained;

[0039] The step of obtaining a pre-stack seismic gather includes obtaining longitudinal wave seismic data through a geophone, processing the longitudinal wave seismic data using a seismic wave longitudinal wave processing method, and obtaining an angle domain CDP gather after removing the dynamic correction tensile distortion; the angle domain CDP gather should contain more than 3 angles, and the angles should be evenly divided, that is, the differences between adjacent angles are equal. The reason and beneficial effect of such a setting are that a linear fitting method is required to obtain the intercept P(t) and the gradient G(t), and more than 3 sample points can ensure that the fitting result is stable. Figure 2The angle domain gathers are divided into four angles for this embodiment. From the figure, we can see that the amplitudes of the 37-degree gather at 3s and the 7-degree gather at 4.2s are significantly different from those at other angles. It can be predicted that the fewer sample points involved in the fitting, the worse the stability of the fitting results.

[0040] Specifically, the second-order Aki-Richards reflection coefficient formula is used to calculate the corresponding intercept P(t) and gradient G(t) for the data of each angle contained in the angle domain CDP gather at time t. The specific algorithm for calculating the intercept P(t) and gradient G(t) using the second-order Aki-Richards reflection coefficient formula can be found in the paper (Shuey R T.1985.Asimplification of the Zoeppritz equtations[j],Geophysics,68(1):29-39.);

[0041] In the actual process of seismic data acquisition, due to the influence of various noises, the noise will be transmitted to the intercept P(t) and gradient G(t). Smoothing the intercept P(t) and gradient G(t) can effectively reduce the influence of noise, such as Figure 3 and Figure 4 Shown are the intercept P(t) and gradient G(t) profiles, respectively.

[0042] S2, calculating an artificial synthetic seismic gather according to the intercept P(t) and the gradient G(t);

[0043] When calculating the synthetic seismic gather, the calculation angle must be consistent with the angle corresponding to the previously obtained angle domain CDP gather. The calculation formula still uses the second-order Aki-Richards reflection coefficient formula. The synthetic seismic gather obtained in this embodiment is as follows: Figure 5 shown.

[0044] S3, calculating the consistency indicator factor of the pre-stack seismic gather and the synthetic seismic gather;

[0045] The calculation formula of consistency indicator factor IF is:

[0046]

[0047] Where a represents the pre-stack seismic gather, b represents the synthetic seismic gather, CC is the correlation coefficient, which indicates the similarity of the change trends of the two, and DIS is the Euclidean distance, which indicates the distance between the two values.

[0048] The calculation formula of CC is:

[0049]

[0050] Among them, m is the starting time of the sampling window, n is the ending time of the sampling window, and a k is the pre-stack seismic gather at the kth sampling moment, is the average value of the prestack seismic gathers within the sampling time window, b k is the artificial synthetic seismic gather at the kth sampling moment, is the average value of the artificially synthesized seismic gathers within the time window calculated for sampling;

[0051] The calculation formula for DIS is:

[0052]

[0053] Among them, m is the starting time of the calculation window, n is the ending time of the calculation window, and a k is the actual gather data at the kth sampling moment (i.e., prestack seismic gather), b k is the artificial synthetic gather data at the kth sampling moment;

[0054] For each angle data in the angle domain CDP gather, the IF values ​​at different angles and times are calculated in combination with the time window length. The time window length can be set arbitrarily, but there are at least two sampling points in the time window. Considering the spatial indicativeness and calculation accuracy of IF, the time window length is preferably set to be equal to one period of the seismic wave.

[0055] In this embodiment, the IF plane diagram of the consistency indicator factor is obtained through step S3 as follows: Figure 6 shown.

[0056] S4, the smaller the difference between the consistency indicator factor and the preset threshold, the better the retention of the AVO feature, and the larger the difference between the consistency indicator factor and the preset threshold, the worse the retention of the AVO feature;

[0057] This step uses the indicator factor IF to evaluate the preservation of the AVO characteristics of the gather. The consistency indicator factor is composed of the cross-correlation and normalized distance between the actual gather data (i.e., pre-stack seismic gather) and the artificially synthesized gather data. Its value ranges from -2 to 1. The closer it is to 1, the more similar the two are and the amplitude values ​​are close. The smaller it is than 1, the more similar the two are and the amplitude values ​​are different. Therefore, the closer the indicator factor is to 1, the better the preservation of the AVO characteristics of the seismic data is, and the farther it is from 1, the worse the preservation of the AVO characteristics is.

[0058] The present invention obtains the intercept and gradient attributes of the pre-stack seismic gather, and calculates the artificially synthesized seismic gather data based on the intercept and gradient attributes. The consistency indicator factor is calculated by combining the correlation coefficient and distance of the similarity between the actual seismic gather and the artificially synthesized gather. The consistency indicator factor is a quantitative value, and its value is between -2 and 1. The closer to 1, the more similar the two are and the amplitude values ​​are close. The smaller than 1, the more similar the two are and the amplitude values ​​are large. Therefore, the closer the indicator factor is to 1, the better the AVO feature preservation of the seismic data is, and the further away from 1, the worse the AVO feature preservation is. The quantitative evaluation result can directly and clearly reflect the preservation of the AVO feature of the gather, greatly improving the accuracy and work efficiency of the evaluation of the AVO feature preservation of the data during the seismic data processing process.

[0059] The method of the present invention can also play a positive role in the process of seismic data processing. It can evaluate the final result gather after the data processing is completed, and can also dynamically evaluate the gather data before and after a certain step or several processing steps during the data processing. If the indicator factor becomes larger, it means that the processing step not only maintains the previous AVO characteristics but also improves the gather quality. On the contrary, if the indicator factor becomes smaller, it means that the processing step destroys the original AVO characteristics. By comparing the changing trends of the indicator factors before and after the processing, the influence of the processing step on the AVO characteristics of the gather can be judged, which helps to optimize the processing flow and processing parameters.

[0060] The rate of change of the indicator factor can be used to optimize the processing flow and reduce inefficient links. For example, the migrated data set usually needs some processing, such as residual time difference correction, energy balancing, denoising, etc. The degree of influence of these processing on the data set quality is reflected by the rate of change of the indicator factor. Steps with large change rates are retained, and steps with small change rates are eliminated. This not only ensures the quality of the data, but also further reduces the processing steps and improves the processing efficiency.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for evaluating the preservation of AVO characteristics of pre-stack seismic gathers, characterized in that: The following steps are included: S1, obtaining a pre-stack seismic gather, and calculating the intercept P(t) and gradient G(t) of the pre-stack seismic gather, where t is the time when the pre-stack seismic gather is obtained; S2, calculating an artificial synthetic seismic gather according to the intercept P(t) and the gradient G(t); S3, calculating the consistency indicator factor of the pre-stack seismic gather and the synthetic seismic gather; the consistency indicator factor is calculated by the following formula: Wherein, a represents the pre-stack seismic gather, b represents the synthetic seismic gather, CC is the correlation coefficient, and DIS is the Euclidean distance; The calculation formula of the Euclidean distance is: Among them, m is the starting time of the sampling window, n is the ending time of the sampling window, is the pre-stack seismic gather at the kth sampling moment, is the artificial synthetic seismic gather at the kth sampling moment; The calculation formula of the correlation coefficient is: Among them, m is the starting time of the sampling window, n is the ending time of the sampling window, is the pre-stack seismic gather at the kth sampling moment, is the average value of the prestack seismic gathers within the sampling time window, is the artificial synthetic seismic gather at the kth sampling moment, is the average value of the artificially synthesized seismic gathers within the time window calculated for sampling; S4: Determine the maintainability of the AVO feature according to the difference between the consistency indicator factor and a preset threshold.

2. The method for evaluating the preservation of AVO characteristics of pre-stack seismic gathers according to claim 1, characterized in that: The calculation formula for the intercept P(t) and gradient G(t) of the pre-stack seismic gather in step S1 is the second-order Aki-Richards reflection coefficient formula.

3. The method for pre-stack seismic gather AVO feature preservation evaluation according to claim 2, characterized in that: Step S1 also includes smoothing the intercept P(t) and gradient G(t) of the calculated pre-stack seismic gather.

4. The method for preserving the AVO characteristics of prestack seismic gathers according to claim 1, wherein: In step S2, the calculation formula for calculating the artificial synthetic seismic gather based on the intercept P(t) and the gradient G(t) is the second-order Aki-Richards reflection coefficient formula.

5. The method for evaluating the preservation of AVO features of pre-stack seismic gathers according to any one of claims 1 to 4, characterized in that: The step of obtaining pre-stack seismic gathers includes obtaining longitudinal wave seismic data through a detector, processing the longitudinal wave seismic data using a seismic wave longitudinal wave processing method, and obtaining an angle domain CDP gather after dynamic correction and removal of dynamic correction tensile distortion.

6. The method for evaluating the preservation of AVO characteristics of pre-stack seismic gathers according to claim 5, characterized in that: The number of angles contained in the angle domain CDP gather should be greater than 3, and the differences between adjacent angles should be equal.

7. An evaluation device for pre-stack seismic gather AVO feature preservation, characterized in that: The invention comprises at least one processor and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method according to any one of claims 1 to 6.

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