OVT domain seismic data processing method

Abstract

The invention belongs to the technical field of seismic exploration, and particularly relates to an OVT domain seismic data processing method. According to the method, after the OVT gathers are divided according to a conventional division mode, the data corresponding to the near-offset gathers are re-divided and re-grouped according to the offset, and the near-offset OVT gathers with the number larger than that of the original OVT division mode are obtained, so that the aim of improving the coverage frequency is achieved, and the imaging precision of the shallow structure is effectively improved; moreover, only the near-offset gathers insensitive to azimuth angles are subjected to offset dimension regrouping, that is, the near-offset data are re-scribed by adopting an offset grouping method, and the far-offset data are still scribed by adopting a conventional OVT grouping method, so that the coverage frequency of a shallow layer is increased, the azimuth information of a middle-deep layer is reserved, and the resolution of the azimuth angles is improved. Imaging precision and data accuracy can be considered, and more accurate data support is provided for pre-stack crack prediction.

Description

Technical Field

[0001] The invention belongs to the technical field of seismic exploration, and in particular relates to an OVT domain seismic data processing method. Background Art

[0002] Conventional prestack time migration is based on common offset data. The azimuth range of the same offset data is 0-180°, and the seismic azimuth cannot be retained after migration. OVT domain prestack time migration can retain seismic azimuth information. OVT vector slices are a collection of seismic data in a specific area in a cross arrangement, with similar azimuth information. We take the average value as the approximate azimuth, which can achieve the purpose of retaining seismic azimuth information to meet the needs of fracture prediction.

[0003] OVT (Offset Vector Tile) is usually translated as "offset vector tile technology". It was first proposed by Vermeer when studying the minimum data set expression of the acquisition area. Conceptually, OVT is a natural extension of the cross-arrangement gather and a data subset within the cross-arrangement gather. The cross-arrangement is obtained by combining all seismic traces from the same shot line and the same receiver line in the orthogonal observation system. It is a data body covered by a word. According to the equal distance division of the shot line distance and the receiver line distance, the cross arrangement can obtain many small rectangles. Each rectangle is an OVT offset vector tile. The size of OVT is determined by the shot line distance and the receiver line distance. The number of OVTs is equal to the number of coverages. Because each OVT is composed of shot points within a limited range along the shot line and receiver points within a limited range along the receiver line, these two ranges limit the value of OVT to a small area, that is, OVT has a limited range of offsets and azimuths. The corresponding OVTs in all cross-arranged gathers are extracted to form an OVT gather, which is composed of seismic traces with approximately the same shot offset and azimuth, and extends to the entire work area. It is a single coverage data volume covering the entire work area.

[0004] Among them, the article "Offset Vector Slice Technology for Wide-azimuth Seismic Processing" in Volume 48, Issue 2 of Petroleum Geophysical Exploration mentioned that OVT is a natural extension of the cross-array gather and a data subset within the cross-array gather. The cross-array can be extracted from the orthogonal observation system, that is, all seismic traces from the same shot line and the same detection line are gathered together, so the number of cross-arrays is the same as the number of intersections between the shot line and the detection line; in a cross-array, many small rectangles are obtained by dividing the shot line distance and the detection line distance at equal distances, and each rectangle is an OVT offset vector slice. The size of OVT is determined by the shot line distance and the detection line distance, and the number of OVT is equal to the number of coverage times. Because each OVT is composed of shot points within a limited range along the shot line and detection points within a limited range along the detection line, these two ranges limit the value of OVT to a small area, that is, OVT has a limited range of shot offsets and azimuths. Extracting the corresponding OVT from all cross-arranged gathers will form an OVT gather, which consists of seismic traces with roughly the same shot offset and azimuth, and extends to the entire work area. It is a single coverage data volume covering the entire work area, so it can be independently offset, so that the azimuth and shot offset information can be saved after the offset for azimuth analysis. The theoretical division method is used above when slicing OVT, and the shallow layer is not taken out for separate consideration, which is not conducive to the fine imaging of shallow structures.

[0005] In the article "High-density wide-azimuth seismic data processing technology based on OVT domain" in the 4th issue of "Western Mining Engineering" in 2017, the data volume of the second coverage area of ​​the observation system can be composed of coordinate-symmetrical OVT, from which the complementarity of OVT can also be observed. A cross-arranged shot point axis can form a new cross-arranged data with another cross-arranged detection point axis. It is proposed to apply the symmetry rule (i.e., OVT slice interchange reconstruction) in data regularization processing, which can reduce the velocity error caused by excessive offset range, reduce mutation points for similar spatial discontinuities, and suppress the acquisition footprint to make up for the rough sampling in the OVT slice. However, it cannot solve the problems of few OVT slices at close offsets, low coverage times, shallow structure imaging and low signal-to-noise ratio.

[0006] Patent CN112630822A "A method and system for processing prestack seismic data in OVT domain" proposes a method and system for processing prestack seismic data in OVT domain. The method includes: sorting the original seismic data according to different azimuths and offsets to obtain OVT domain gathers; decomposing the data into instantaneous amplitude and instantaneous phase in the OVT domain; selecting and processing the center plane element, and superimposing the gathers within a certain spatial range of the center plane element based on the superposition principle; repeating the above processing steps for all center plane elements to obtain the results of all processed center plane elements, and reconstructing the output phase data and amplitude data. By sorting the original data into OVT gathers with different offsets and different azimuths, using the signal correlation in the OVT gathers, the effective weak reflection signals masked by noise are enhanced on the basis of preserving the phase, and the overall signal-to-noise ratio of the prestack data is improved, so that the prestack gathers, stacking and imaging profile effects are significantly improved. Based on the demonstrated situation, this method has the following two problems: 1. In actual seismic data, especially mountain data, if there are large holes in the selected processing center element, the output phase data and amplitude data will be discontinuous, affecting the next step of data reconstruction; 2. There are few near-offset data. If the effective reflection signal in the shallow layer is too weak, the fidelity of the reconstructed data will be questionable.

[0007] In summary, in the current OVT domain processing of seismic data, the OVT theoretical bin size is basically fixed equal to 2 times the shot line spacing * 2 times the detection line spacing; compared with the common offset data, the shallow signal-to-noise ratio and imaging problems are not considered when slicing the OVT domain data. The offset range of each OVT slice is large, which makes the number of OVT slices with close offsets small, resulting in low shallow coverage times and signal-to-noise ratio, which is not conducive to the fine imaging of shallow structures, resulting in low shallow structure imaging accuracy. Summary of the invention

[0008] The object of the present invention is to provide an OVT domain seismic data processing method for solving the problem in the prior art that when OVT domain data is sliced, the offset range of each OVT slice is large, resulting in low shallow structure imaging accuracy.

[0009] In order to achieve the above object, the present invention provides an OVT domain seismic data processing method, comprising the following steps:

[0010] After dividing the acquired original seismic data into OVT gathers and performing data processing, the first seismic data is obtained;

[0011] According to the set offset, data corresponding to the near-offset gathers in the first seismic data are re-divided to obtain new OVT gathers; the number of the new OVT gathers is greater than the number of the near-offset gathers before re-dividing; the near-offset gathers are OVT gathers containing data with an offset less than a set threshold;

[0012] Processed OVT domain seismic data are obtained based on the new OVT gather and other OVT gathers in the first seismic data except the close offset gather.

[0013] The beneficial effects of the above technical solution are as follows: after the OVT gathers are divided according to the conventional division method, the data corresponding to the near-offset gathers are re-divided and re-grouped according to the offset, so as to obtain a larger number of near-offset OVT gathers than the original OVT division method, thereby achieving the purpose of increasing the number of coverages and effectively improving the imaging accuracy of shallow structures; and the near-offset data are re-sliced ​​using the offset grouping method, while the far-offset data are still sliced ​​using the conventional OVT grouping method, which not only increases the number of shallow coverages, but also retains the azimuth information of the middle and deep layers, and can take into account both imaging accuracy and data accuracy, providing more accurate data support for pre-stack fracture prediction.

[0014] Furthermore, according to the set offset, the data corresponding to the near-offset gather in the first seismic data is re-divided in the following manner:

[0015] The data corresponding to the near-offset gathers in the first seismic data are re-divided into a number of new OVT gathers at intervals of a set offset.

[0016] Furthermore, according to the new OVT gather and other OVT gathers except the close offset gather in the first seismic data, the processed OVT domain seismic data is obtained as follows:

[0017] The new OVT gather is merged with other OVT gathers except the close offset gathers in the first seismic data, and random noise is suppressed on the merged data;

[0018] The data after random noise suppression is regularized to obtain processed OVT domain seismic data.

[0019] The beneficial effect of the above technical solution is: random noise is suppressed on the data obtained by merging the new OVT gather with other OVT gathers in the first seismic data except the near-offset gather, which significantly improves the signal-to-noise ratio of each piece of data and enhances the effective weak reflection signal masked by the noise.

[0020] Furthermore, the data regularization includes high-precision four-dimensional interpolation; the difference dimensions of the high-precision four-dimensional interpolation include InLine, CrossLine, azimuth and time.

[0021] The beneficial effect of the above technical solution is that empty facets can be filled through high-precision four-dimensional interpolation processing.

[0022] Furthermore, the data regularization also includes facet centering.

[0023] The beneficial effect of the above technical solution is that through the facet centering processing, the reflection point in the facet can be located at the center of the facet, ensuring uniform distribution of data.

[0024] Furthermore, the value of the set offset is determined according to the distance between the detection points.

[0025] Furthermore, after the data processing, the first seismic data is obtained by performing interchangeable reconstruction processing on the OVT gathers obtained after the original seismic data are divided to obtain the first seismic data.

[0026] The beneficial effects of the above technical solution are: it can reduce the offset range and preliminarily increase the number of near-offset OVT gathers.

[0027] Furthermore, the acquired original seismic data is data obtained by preprocessing the actually collected seismic data and then extracting it into a cross-arranged gather.

[0028] Furthermore, when the acquired original seismic data is divided into OVT gathers, the OVT theoretical bin size is determined according to the shot line spacing and the detection line spacing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flowchart of the OVT domain seismic data processing method in the embodiment of the OVT domain seismic data processing method of the present invention;

[0030] Figure 2 It is a schematic diagram of performing an interchange and reconstruction process on OVT slices in an embodiment of the OVT domain seismic data processing method of the present invention;

[0031] Figure 3a It is a schematic diagram of the offset range before the OVT slices are interchanged and reconstructed in the embodiment of the OVT domain seismic data processing method of the present invention;

[0032] Figure 3b It is a schematic diagram of the offset range after the OVT slices are interchanged and reconstructed in the embodiment of the OVT domain seismic data processing method of the present invention;

[0033] Figure 4 It is a schematic diagram of re-dividing the data corresponding to the near-offset gather in the embodiment of the OVT domain seismic data processing method of the present invention;

[0034] Figure 5 It is a schematic diagram of seismic data E obtained after random noise suppression processing is performed on seismic data D in an embodiment of the OVT domain seismic data processing method of the present invention;

[0035] Figure 6 It is a schematic diagram of gather data F obtained after data regularization is performed on seismic data E in an embodiment of the OVT domain seismic data processing method of the present invention;

[0036] Figure 7 It is a schematic diagram of the original migration profile corresponding to the OVT slice division according to the existing 2 times shot line spacing * 2 times detection line spacing in the embodiment of the OVT domain seismic data processing method of the present invention;

[0037] Figure 8 It is a schematic diagram of the original offset profile corresponding to the OVT domain seismic data processing method of the present invention in the embodiment of the OVT domain seismic data processing method of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0039] OVT domain seismic data processing method embodiment

[0040] This embodiment provides a technical solution for an OVT domain seismic data processing method. Figure 1 , including the following steps:

[0041] 1) After performing OVT gather division and data processing on the acquired original seismic data, the first seismic data is obtained;

[0042] In this embodiment, the original seismic data obtained is recorded as seismic data B; specifically, the seismic data actually collected is preprocessed to obtain seismic data A, and then the seismic data A is subjected to data preparation (the data preparation method in this embodiment is to extract the seismic data A into a cross-arranged track set) to obtain seismic data B.

[0043] After data processing, the first seismic data is obtained by performing interchangeable reconstruction processing on the OVT gathers obtained after dividing the acquired original seismic data (i.e., seismic data B) to obtain the first seismic data. Wherein, when the acquired original seismic data is divided into OVT gathers, the OVT theoretical facet size is determined according to the shot line spacing and the detection line spacing. Specifically, in this embodiment, the seismic data B is divided into OVT slices according to 2 times the shot line spacing * 2 times the detection line spacing (i.e., corresponding to the OVT gather division), and the divided OVT slices are interchangeably reconstructed, thereby reducing the offset range and obtaining seismic data C (i.e., the first seismic data). Refer to the interchangeable reconstruction processing method. Figure 2 The specific operation process belongs to the prior art and will not be described here.

[0044] 2) According to the set offset, the data corresponding to the near-offset gathers in the first seismic data are re-divided to obtain new OVT gathers; wherein the number of new OVT gathers is greater than the number of near-offset gathers in the first seismic data before re-division; the near-offset gathers are OVT gathers containing data with an offset less than a set threshold; as long as there are data with an offset less than the set threshold in the OVT gathers, they are identified as OVT gathers containing data with an offset less than the set threshold.

[0045] The redivision method is: the data corresponding to the near-offset gather in the first seismic data is redivided into several new OVT gathers with the set offset as the interval; the value of the set offset is determined according to the distance between the detection points. In this embodiment, the offset is set to half of the distance between the detection points. For example, if the distance between the detection points is 50 meters, the value of the set offset is 25 meters.

[0046] Specifically, in this embodiment, the threshold is set to 1000m, that is, the OVT slices involving offsets in the range of 0-1000 in the seismic data C are regrouped according to the offset (wherein the OVT slices involving offsets in the range of 0-1000 are OVT gathers containing data with offsets less than the set threshold), so that the number of new OVT gathers obtained by regrouping is greater than the number of near-offset gathers in the first seismic data before re-division, that is, the near-offset gathers are further subdivided according to the offset, so that the number of slices obtained by grouping is greater, thereby increasing the number of coverage times by increasing the number of grouped slices, thereby achieving the purpose of improving the signal-to-noise ratio; because regrouping the data according to the offset is equivalent to only focusing on the grouping of the data in the offset dimension, without considering the direction of the data Therefore, part of the accuracy of the azimuth dimension will be lost, but since the near-offset data is not sensitive to the azimuth, the OVT domain seismic data processing method of this embodiment only regroups the offset dimension for the near-offset gathers with relatively messy azimuth information, that is, the near-offset data are re-sliced ​​using the offset grouping method, and the far-offset data are sliced ​​using the conventional OVT grouping method, which not only improves the coverage times of the shallow layer, but also retains the azimuth information of the medium and deep layers, can take into account both the imaging accuracy and the data accuracy, provides more accurate data support for pre-stack fracture prediction, and can effectively improve the imaging accuracy of the shallow structure; although this method sacrifices the accuracy of the azimuth of the near-offset data to a certain extent, the impact on the overall data is within an acceptable range.

[0047] 3) Based on the new OVT gathers and other OVT gathers except the close offset gathers in the first seismic data, the processed OVT domain seismic data is obtained, specifically:

[0048] The new OVT gather is merged with other OVT gathers except the near-offset gather in the first seismic data, and random noise is suppressed on the merged data; the merging here refers to putting the new OVT gather and other OVT gathers except the near-offset gather in the first seismic data together to form a data set containing several OVT gathers.

[0049] The data after random noise suppression is regularized to obtain processed OVT domain seismic data.

[0050] In this embodiment, after the OVT slices involving offset distances in the range of 0-1000 in the seismic data C are regrouped according to the offset distance, the regrouped data are put together with other unmodified data (i.e., other OVT gathers except the near-offset gathers in the first seismic data) to obtain seismic data D; random noise suppression processing is performed on the seismic data D to prepare data for the next step of data regularization processing to obtain seismic data E; since the seismic traces in each slice have similar offset distances and azimuths, the signals between the seismic traces are correlated, and the random noise is irregular, therefore, random noise suppression processing can significantly improve the signal-to-noise ratio of each slice of data and enhance the effective weak reflection signal masked by the noise.

[0051] Among them, data regularization includes high-precision four-dimensional interpolation and facet centering; the difference dimensions of high-precision four-dimensional interpolation include InLine, CrossLine, azimuth and time; through high-precision four-dimensional interpolation processing, empty facets are filled, and through facet centering processing, the reflection point in the facet is located at the facet center to ensure uniform data distribution. Under the premise of maintaining fidelity and radiation, this embodiment adopts multi-dimensional Fourier regularization technology, converts each frequency slice to the space-frequency domain through anti-leakage Fourier transform, and then reconstructs the energy to the facet center through inverse Fourier transform to achieve multi-dimensional data regularization; data regularization is performed on seismic data E to obtain the final gather data F as the processed OVT domain seismic data, which is the processing result of the OVT domain seismic data processing method of this embodiment.

[0052] The following is a detailed description of the specific implementation process of the OVT domain seismic data processing method of this embodiment, taking a certain three-dimensional seismic data of northeastern Sichuan as an example:

[0053] 1) Obtain the preprocessed seismic data A and prepare the data; first extract the cross-arranged gathers to obtain seismic data B. Divide the seismic data B into OVT slices according to 2 times the shot line spacing * 2 times the detection line spacing (the OVT slices here and below refer to the OVT gathers, and the number of slices refers to the number of OVT gathers), and perform interchangeable reconstruction. Figure 2 , reduce the offset range (refer to Figure 3a and Figure 3b), obtain seismic data C.

[0054] 2) In seismic data C, there are 14 OVT slices with an offset distance of less than 1000. Among them, the offset range of slice 5050 (here 5050 is only the preset OVT gather number, not the value of a certain parameter) is 1-497, and the azimuth range is 0-360; the offset range of slice 4949 is 447-892, and the azimuth range is 0-360; the offset range of slice 5048 is 721-1125, and the azimuth range is 42-302. The 14 OVT slices with an offset distance of 0-1000 in seismic data C are regrouped according to the offset distance (such as Figure 4 As shown in FIG. 1 , specifically, these original near-offset OVT slices are re-divided into 56 groups at an offset interval of 25 meters, thereby increasing the number of data slices and achieving the purpose of increasing the number of times the front-layer data is covered; while the OVT slices not involving an offset within 1000 still maintain the existing OVT domain division result of 2 times the shot line spacing * 2 times the detection line spacing; these two types of data are combined to obtain seismic data D.

[0055] 3) Suppress the random noise of seismic data D to prepare data for the next step of data regularization processing, and obtain seismic data E (refer to Figure 5 ).

[0056] 4) Regularize the seismic data E to obtain the final gather data F (refer to Figure 6 ). Data regularization includes high-precision four-dimensional interpolation (InLine, CrossLine, azimuth, time) and bin centering. Through high-precision four-dimensional interpolation processing, empty bins are filled, and through bin centering processing, the reflection point in the bin is placed at the center of the bin, ensuring uniform data distribution.

[0057] contrast Figure 7 (Schematic diagram of the original migration profile corresponding to the OVT slice division according to 2 times the shot line spacing * 2 times the detection line spacing) and Figure 8 (Schematic diagram of the original offset profile corresponding to the OVT domain seismic data processing method of the present embodiment) It can be seen that after the near-offset data are regrouped and the data are regularized, the OVT domain seismic data processing method of the present embodiment improves the signal-to-noise ratio of shallow data, enhances the effective reflection information, and significantly improves the imaging accuracy of shallow structures. Therefore, the present method has made great progress in improving the signal-to-noise ratio and imaging accuracy of shallow data.

[0058] The present invention has the following characteristics:

[0059] 1) After the OVT gathers are divided according to the conventional division method, the data corresponding to the near-offset gathers are re-divided and regrouped according to the offset, so as to obtain more near-offset OVT gathers than the original OVT division method, thereby achieving the purpose of increasing the number of coverage times and effectively improving the imaging accuracy of shallow structures.

[0060] 2) Only the near-offset gathers that are insensitive to azimuth are regrouped in the offset dimension, that is, the near-offset data are re-sliced ​​using the offset grouping method, while the far-offset data are still sliced ​​using the conventional OVT grouping method. This not only increases the coverage of the shallow layer, but also retains the azimuth information of the middle and deep layers, and can take into account both imaging accuracy and data accuracy, providing more accurate data support for pre-stack fracture prediction.

[0061] 3) The random noise of the data after the new OVT gather is merged with the other OVT gathers in the first seismic data except the near-offset gather is suppressed, which significantly improves the signal-to-noise ratio of each piece of data and enhances the effective weak reflection signals masked by noise.

[0062] 4) Regularize the data after random noise suppression so that the empty bins are filled and the reflection points in the bins are located at the center of the bins to ensure uniform data distribution.

[0063] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, but do not constitute a limitation to the present invention.

Claims

1. A method for processing seismic data in OVT domain, characterized in that: The steps include: After dividing the acquired original seismic data into OVT gathers and performing data processing, the first seismic data is obtained; According to the set offset, data corresponding to the near-offset gathers in the first seismic data are re-divided to obtain new OVT gathers; the number of the new OVT gathers is greater than the number of the near-offset gathers before re-dividing; the near-offset gathers are OVT gathers containing data with an offset less than a set threshold; Processed OVT domain seismic data are obtained based on the new OVT gather and other OVT gathers in the first seismic data except the close offset gather.

2. The OVT domain seismic data processing method according to claim 1, characterized in that: According to the set offset, the data corresponding to the near-offset gather in the first seismic data is re-divided in the following manner: The data corresponding to the near-offset gathers in the first seismic data are re-divided into a number of new OVT gathers at intervals of a set offset.

3. The OVT domain seismic data processing method according to claim 1 or 2, characterized in that: According to the new OVT gather and other OVT gathers except the close offset gather in the first seismic data, the processed OVT domain seismic data is obtained as follows: The new OVT gather is merged with other OVT gathers except the close offset gathers in the first seismic data, and random noise is suppressed on the merged data; The data after random noise suppression is regularized to obtain processed OVT domain seismic data.

4. The OVT domain seismic data processing method according to claim 3, characterized in that: The data regularization includes high-precision four-dimensional interpolation; the difference dimensions of the high-precision four-dimensional interpolation include InLine, CrossLine, azimuth and time.

5. The OVT domain seismic data processing method according to claim 4, characterized in that: The data regularization also includes facet centering.

6. The OVT domain seismic data processing method according to claim 1 or 2, characterized in that: The value of the set offset is determined according to the distance between the detection points.

7. The OVT domain seismic data processing method according to claim 1 or 2, characterized in that: After the data processing, the first seismic data is obtained by performing interchangeable reconstruction processing on the OVT gathers obtained after the original seismic data are divided to obtain the first seismic data.

8. The OVT domain seismic data processing method according to claim 1 or 2, characterized in that: The original seismic data obtained are data obtained by preprocessing the actually collected seismic data and then extracting them into a cross-arranged gather.

9. The OVT domain seismic data processing method according to claim 1 or 2, characterized in that: When the acquired original seismic data is divided into OVT gathers, the OVT theoretical bin size is determined according to the shot line spacing and the detector line spacing.

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