A method and system for efficient modeling of near-surface velocity using first-arrival tomography

Abstract

The present invention relates to a first-arrival tomographic near-surface velocity efficient modeling method, which uses data in a cross-corridor region for tomographic inversion, significantly improving computational efficiency with relatively small precision loss. The method comprises the following main steps: (1) inputting parameters defining the cross-corridor region, (2) determining a rectangular region along the x-axis direction and a rectangular region along the y-axis direction to constitute the cross-corridor region, (3) determining the plane range of the velocity model involved in the forward modeling, (4) extracting a subset of receiving points belonging to the cross-corridor region, and (5) constructing a velocity model involved in the forward modeling and performing ray tracing to obtain the ray path and travel time. The first-arrival tomographic near-surface velocity efficient modeling method provided by the present invention has significantly improved efficiency with relatively small precision loss in the first-arrival tomographic near-surface velocity modeling.

Description

Technical Field

[0001] The invention belongs to the field of geophysical exploration, and in particular relates to a first-arrival tomographic near-surface velocity efficient modeling method and system. Background Art

[0002] The near-surface velocity modeling technology of first-arrival tomography in seismic exploration is a technology that uses the first-arrival time to invert the near-surface velocity model, and is widely used in the process of seismic data processing. The near-surface velocity modeling technology of first-arrival tomography is an iterative process, and each iterative operation includes two basic steps: forward modeling and inversion. The forward modeling step uses ray tracing technology to calculate the ray path and travel time experienced by the seismic waves that are excited at each shot point and propagate through a given initial velocity model and reach each receiving point; the inversion step is to calculate the modification amount of the initial velocity model based on the difference between the travel time obtained by the forward modeling and the first-arrival time picked up by the actual data, combined with the ray path data obtained by the forward modeling. The velocity model obtained by applying the initial velocity model modification amount calculated by the inversion process to the initial velocity model is used as the initial velocity model for the next iteration and enters the next iteration.

[0003] The forward modeling process is the step that consumes the most CPU computing time in the first-arrival tomographic near-surface velocity modeling technology. Although different ray tracing technologies are available, the CPU computing time consumed by ray tracing is related to the velocity model range used to calculate the ray path during the ray tracing process. The larger the velocity model range used, the more CPU computing time is consumed, and the increase in the CPU computing time is greater than the increase in the velocity model range used. The range of receiving points for each shot data used for first-arrival tomographic near-surface velocity modeling is an important factor in determining the range of the velocity model used in the forward modeling process. The range of the velocity model on the plane should not be less than the range covered by the receiving points. After the seismic exploration data is collected, the observation system (the relative relationship between the shot point and the receiving point) is determined. Most of the existing technologies use the shot point as the center, and use a circular area or a rectangular area to delineate the range of receiving points for each shot data used for first-arrival tomographic near-surface modeling. The range of the receiving points determines the plane range of the velocity model involved in the forward modeling of the corresponding shot point. The velocity model actually involved in the forward modeling is composed of the velocity model in the plane range of the velocity model involved in the forward modeling, which is intercepted from the overall velocity model corresponding to the entire work area. An important factor that determines the efficiency is the range of the velocity model involved in the forward modeling. In theory, the larger the range of receiving points of each shot data used for the first-arrival tomographic near-surface velocity modeling, the more beneficial it is to improve the accuracy of the inverted near-surface velocity model. Using all the receiving points corresponding to the shot point for the first-arrival tomographic near-surface velocity modeling, that is, using the data of all shot offsets (the distance from the shot point to the receiving point) and all shot azimuths (the azimuth of the line connecting the shot point to the receiving point) contained in the observation system, is most beneficial to improving the accuracy of the inverted near-surface velocity model. However, a too large range of receiving points requires a larger range of velocity models during the forward modeling process, which will increase the CPU computing time and lead to a decrease in the efficiency of the first-arrival tomographic near-surface velocity modeling. At the same time, the larger the range of receiving points of each shot data used for the first-arrival tomographic near-surface velocity modeling, the larger the amount of data involved in the inversion step. The exploration work area with a large number of shot points will also increase the difficulty of implementing the inversion step and the consumption of computing resources.

[0004] There are two main factors that affect the accuracy of first-arrival tomography near-surface velocity modeling: one is the algorithm, and the other is the range of first-arrival data used. The impact of first-arrival data on modeling accuracy can be decomposed into two aspects: one is the distribution of offsets, and the other is the distribution of offset azimuths. In terms of offset distribution, near-offset data contributes to the accuracy of shallow velocity models, and far-offset data mainly contributes to the accuracy of relatively deep velocity models, that is, the accuracy of first-arrival tomography near-surface velocity modeling in the depth direction is mainly affected by the offset distribution. The ideal offset distribution requires as large a range as possible from small offset to large offset, as uniform a distribution as possible, and a sufficiently large density. The offset azimuth distribution mainly contributes to the accuracy of the velocity model along different azimuths. The ideal offset azimuth distribution requires a full range from 0 to 360 degrees, as uniform a distribution as possible, and a sufficiently large density.

[0005] The near-surface velocity model established by the first-arrival tomography near-surface velocity modeling technology is an expression of the changing trend of the true near-surface velocity model. It is currently mainly used for the calculation of static correction and for the establishment of the initial velocity model of pre-stack depth migration. In such an application scenario, the higher the accuracy of the near-surface velocity model established by the first-arrival tomography, the better. However, it is also very important to balance the accuracy and efficiency. It is necessary to adopt some methods to improve efficiency, as long as the established near-surface velocity model can grasp the changing trend of the true near-surface velocity model, because the difference between the near-surface velocity model established by the first-arrival tomography near-surface velocity modeling technology and the true velocity model can be compensated by various existing high-frequency time correction methods. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for efficiently modeling near-surface velocity of first-arrival tomography, comprising the steps of:

[0007] S10, determining a preset area by using n preset azimuth angles and the maximum offset used, wherein n is a natural number ranging from 2 to 8;

[0008] S20, determining the plane range of the velocity model involved in the forward modeling according to the preset area;

[0009] S30, extracting a subset of receiving points located in the preset area from the shot data of the current shot point;

[0010] S40, constructing a velocity model participating in forward modeling according to the plane range of the velocity model participating in forward modeling, and calculating the ray path and travel time from the shot point to each receiving point in the receiving point subset by using ray tracing technology.

[0011] Wherein, in the step S10, the n is 4, and the preset area is composed of a first rectangular area along the receiving line direction and a second rectangular area along the direction perpendicular to the receiving line.

[0012] The width of the first rectangular area is greater than the distance between two adjacent receiving lines; the width of the second rectangular area is greater than the distance between two adjacent receiving points; and half of the length of the first rectangular area and the second rectangular area is the maximum offset used.

[0013] Among them, in the step S20, the plane range of the velocity model of the first rectangular area participating in the forward modeling includes the range after the first rectangular area is expanded outward by a given distance in the length direction and the width direction of the first rectangular area respectively on the basis of the first rectangular area; the plane range of the velocity model of the second rectangular area participating in the forward modeling includes the range after the second rectangular area is expanded outward by a given distance in the width direction and the length direction of the second rectangular area respectively on the basis of the second rectangular area.

[0014] Wherein, in the step S30, the receiving point subset includes a receiving point subset formed by superimposing a receiving point subset 1 in the first rectangular area and a receiving point subset 2 in the second rectangular area and removing duplicate data.

[0015] Wherein, the step S40 includes: respectively calculating the ray path and travel time from the shot point to each receiving point in the receiving point subset belonging to the first rectangular area and the ray path and travel time from the shot point to each receiving point in the receiving point subset belonging to the second rectangular area and eliminating duplicate data.

[0016] The present invention also provides a first-arrival tomography near-surface velocity efficient modeling system, comprising:

[0017] A preset area determination unit: determines the preset area by using n preset azimuth angles and the maximum offset used, wherein n is a natural number ranging from 2 to 8;

[0018] A plane range determination unit for the velocity model involved in the forward modeling is used to determine the plane range of the velocity model involved in the forward modeling according to the preset area;

[0019] A receiving point subset extraction unit: extracting a receiving point subset located in the preset area from the shot data of the current shot point;

[0020] The ray path and travel time calculation unit of the receiving point: constructs the velocity model participating in the forward modeling according to the plane range of the velocity model participating in the forward modeling, and calculates the ray path and travel time from the shot point to each receiving point in the receiving point subset by using the ray tracing technology.

[0021] Wherein, n is 4, and the preset area is composed of a first rectangular area along the receiving line direction and a second rectangular area along the direction perpendicular to the receiving line.

[0022] The width of the first rectangular area is greater than the distance between two adjacent receiving lines; the width of the second rectangular area is greater than the distance between two adjacent receiving points; and half of the length of the first rectangular area and the second rectangular area is the maximum offset used.

[0023] The present invention also provides a computer-readable storage medium, characterized in that: the computer-readable storage medium stores at least one program executable by a computer, and when the at least one program is executed by the computer, it is the steps in the above-mentioned first-arrival tomography near-surface velocity efficient modeling method.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The method for efficiently modeling near-surface velocity of first-arrival tomography provided by the present invention uses a cross-corridor area to delineate the range of receiving points of each shot data used for first-arrival tomography near-surface velocity modeling, thereby effectively reducing the range of velocity models used in the forward modeling step, thereby improving the efficiency of first-arrival tomography near-surface velocity modeling, and at the same time, does not cause significant loss in the accuracy of near-surface modeling.

[0026] The first-arrival tomographic near-surface velocity efficient modeling method provided by the present invention has significantly improved efficiency at the expense of relatively small first-arrival tomographic near-surface velocity modeling accuracy loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the cross corridor area provided by the present invention

[0028] Figure 2 Distribution diagram of the work area blasting points and receiving points of the theoretical model provided by the present invention

[0029] Figure 3 The overall velocity model plane distribution diagram of the entire work area of ​​the theoretical model provided by the present invention and three velocity quality control lines (AB, CD, EF)

[0030] Figure 4 Observation system diagram of a shot point of the theoretical model provided by the present invention

[0031] Figure 5 The cross corridor area of ​​a shot point and its receiving point provided by the theoretical model of the present invention

[0032] Figure 6 The theoretical model provided by the present invention corresponds to Figure 3 The velocity profiles of the three velocity quality control lines (from top to bottom correspond to Figure 3 EF, CD, AB line positions in

[0033] Figure 7The velocity model provided by the present invention using full-angle, full-offset data tomography inversion corresponds to Figure 3 The velocity profiles of the three velocity quality control lines (from top to bottom correspond to Figure 3 EF, CD, AB line positions in the

[0034] Figure 8 The velocity model provided by the present invention using the cross corridor regional data tomography inversion corresponds to Figure 3 The velocity profiles of the three velocity quality control lines (from top to bottom correspond to Figure 3 EF, CD, AB line positions in

[0035] Fig. 9 This is a flowchart of the steps of Embodiment 2 of the present invention.

[0036] Fig.10 The structural diagram of the second embodiment of the present invention DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0038] In the first-arrival tomography near-surface velocity modeling technology, the azimuth distribution of shot detection mainly contributes to the accuracy of the velocity model along different azimuths. The ideal azimuth distribution of shot detection is required to be omnidirectional from 0 to 360 degrees. In the specific implementation process, 2 to 8 azimuths can be selected for receiving point data collection.

[0039] The method of using the cross corridor area to delineate the receiving point range of each shot data used for first-arrival tomography near-surface velocity modeling is adopted, that is, in terms of azimuth distribution, only the receiving point data near the four azimuths of 0, 90, 180, and 270 degrees are used, and in terms of offset distribution, all the receiving point data within the range from 0 offset to the given maximum offset used are used. Figure 1 The figure shows the schematic diagram of the cross corridor area used in this method. In this way, the plane range of the velocity model participating in the forward modeling intercepted from the overall velocity model corresponding to the entire work area is only within the cross corridor area, reducing the range of the velocity model participating in the forward modeling. Practice has proved that this method can effectively reduce the range of the velocity model used in the forward modeling step, thereby improving the efficiency of the first-arrival tomographic near-surface velocity modeling, while not causing significant loss in the accuracy of the established near-surface velocity model.

[0040] Example 1

[0041] like Fig. 9The present embodiment provides a first arrival tomographic near-surface velocity efficient modeling method, comprising the steps of:

[0042] S10, determining a preset area by using n preset azimuth angles and the maximum offset used, wherein n is a natural number ranging from 2 to 8;

[0043] Determine a coordinate system, with the shot point as the coordinate origin, the x-axis is selected along the receiving line direction or along the direction perpendicular to the receiving line, the n is 4, the azimuth angle is selected from 0 degrees, 90 degrees, 180 degrees and 270 degrees, and the preset area is composed of a first rectangular area with a length along the receiving line direction and a second rectangular area with a length along the direction perpendicular to the receiving line.

[0044] The half width of the first rectangular area is greater than the distance between two adjacent receiving lines, i.e., half of the receiving line spacing; the half width of the second rectangular area is greater than the spacing between two receiving points on the receiving line, i.e., half of the track spacing. The half length of the length of the two rectangular areas is the maximum shot offset used.

[0045] The maximum offset used is a parameter that is less than or equal to the maximum offset of the actual collected data and is determined by experiment. A representative part of the processing area is selected, starting from the maximum offset of the actual collected data as the test offset, and the test offset is gradually reduced to perform first-arrival tomographic near-surface velocity modeling. The minimum test offset that can meet the accuracy requirements of near-surface velocity modeling is selected from the results to be determined as the maximum offset used, which is used as the maximum offset parameter used for the final first-arrival tomographic near-surface velocity modeling, that is, the half-side length of the length of the two rectangular areas.

[0046] In an observation system that does not use wide azimuth acquisition, the maximum offset along the receiving line direction (i.e., the maximum value of the absolute value of the coordinate difference between the shot point and the receiving point on the coordinate axis along the receiving line direction) is greater than the maximum offset in the direction perpendicular to the receiving line (i.e., the maximum value of the absolute value of the coordinate difference between the shot point and the receiving point on the coordinate axis along the direction perpendicular to the receiving line). The maximum offset used obtained by the above test may be greater than the maximum offset in the direction perpendicular to the receiving line of the acquisition observation system. In this case, the offset obtained by the test is used as the maximum offset used as the half-side length of the first rectangular area along the receiving line direction, and the maximum offset in the direction perpendicular to the receiving line of the acquisition observation system is used as the half-side length of the second rectangular area along the direction perpendicular to the receiving line.

[0047] S20, determining the plane range of the velocity model involved in the forward modeling according to the preset area;

[0048] The plane range of the velocity model in which the first rectangular area participates in the forward modeling is included in the range expanded outward by a given distance in the x-axis direction and the y-axis direction on the basis of the first rectangular area; the plane range of the velocity model in which the second rectangular area participates in the forward modeling is included in the range expanded outward by a given distance in the x-axis direction and the y-axis direction on the basis of the second rectangular area.

[0049] S30, extracting a subset of receiving points located in the preset area from the shot data of the current shot point;

[0050] The receiving point subset refers to a receiving point subset formed by superimposing a receiving point subset 1 within the first rectangular area and a receiving point subset 2 within the second rectangular area and removing duplicate data.

[0051] S40, constructing a velocity model participating in the forward modeling according to the plane range of the velocity model participating in the forward modeling, that is, intercepting the velocity model within the plane range of the velocity model participating in the forward modeling from the overall velocity model corresponding to the entire work area to form the velocity model participating in the forward modeling, and then calculating the ray path and travel time from the shot point to each receiving point in the receiving point subset by using ray tracing technology;

[0052] The ray path and travel time from the shot point to each receiving point in the receiving point subset belonging to the first rectangular area and the ray path and travel time from the shot point to each receiving point in the receiving point subset belonging to the second rectangular area are calculated respectively, and duplicate data are eliminated.

[0053] A computer-readable storage medium stores at least one computer-executable program, which, when executed by the computer, enables the computer to execute the steps in a first-arrival tomographic near-surface velocity efficient modeling method.

[0054] Example 2

[0055] like Figure 1 As shown, Embodiment 2 of the present invention provides a method of using a cross-corridor region to delineate the range of receiving points of each shot data used for first-arrival tomographic near-surface velocity modeling. Considering that the increase ratio of the CPU operation time consumed in the forward modeling step is greater than the increase ratio of the velocity model range used, in order to improve efficiency, the cross-corridor region is further decomposed into a rectangular region along the x-axis direction and a rectangular region along the y-axis direction for processing and then merged.

[0056] The forward modeling process of first-arrival tomographic near-surface velocity modeling is to calculate the ray path and travel time from the shot point to the receiving point shot by shot. The cross corridor area is delineated as the receiving point range of each shot data used for first-arrival tomographic near-surface velocity modeling. The following steps need to be specially considered for each shot in the forward modeling process.

[0057] Step 1, determine the cross corridor area composed of a rectangular area along the x-axis direction and a rectangular area along the y-axis direction. A coordinate axis of a shot point data is agreed upon, with the shot point as the origin, and the x-axis direction can be selected between the direction along the receiving line and the direction perpendicular to the receiving line, that is, the x-axis direction can be taken along the receiving line direction or along the direction perpendicular to the receiving line direction. Usually, the x-axis direction is taken along the receiving line direction. Four parameters define the cross corridor area, XLIMIT_h, YLIMIT_h, XLIMIT_v, YLIMIT_v, where the first two parameters define the rectangular area of ​​the cross corridor area along the x-axis direction ( Figure 1 The second two parameters define the rectangular area of ​​the cross corridor area along the y-axis direction ( Figure 1 =Rectangle EFGH in the middle. XLIMIT_h is the half-side length of the rectangular area along the x-axis in the x-axis direction (i.e., the length of AD is equal to twice XLIMIT_h), and YLIMIT_h is the half-side length of the rectangular area along the x-axis in the y-axis direction (i.e., the length of AB is equal to twice YLIMIT_h). XLIMIT_v is the half-side length of the rectangular area along the y-axis in the x-axis direction (i.e., the length of EF is equal to twice XLIMIT_v), and YLIMIT_v is the half-side length of the rectangular area along the y-axis in the y-axis direction (i.e., the length of FG is equal to twice YLIMIT_v). The rectangular area along the x-axis and the rectangular area along the y-axis together constitute the cross corridor area. XLIMIT_h and YLIMIT_v determine the maximum offset of the rectangular area along the x-axis and along the y-axis in each shot data used for first-arrival tomography near-surface velocity modeling. YLIMIT_h and XLIMIT_v are the widths of the rectangular area along the x-axis and the rectangular area along the y-axis in the cross corridor area, respectively. The relationship between the parameters defining the cross corridor area should conform to XLIMIT_v<XLIMIT_h, YLIMIT_v> YLIMIT_h.

[0058] Further explanation of the four parameters that define the cross corridor area. When the direction along the receiving line is taken as the x-axis direction, YLIMIT_h is generally taken to be greater than or equal to the line spacing of the receiving line, which can ensure that there are at least two receiving points of the receiving lines in the rectangular area along the x-axis direction. The larger the YLIMIT_h, the more receiving lines may be contained in the rectangular area along the x-axis direction, and the accuracy of the tomographic inversion result will be relatively higher but the efficiency will be relatively lower. When YLIMIT_h is equal to the line spacing of the receiving lines, there are exactly two receiving points of the receiving lines in the rectangular area along the x-axis direction. When YLIMIT_h is less than the line spacing of the receiving lines but greater than or equal to half of the line spacing of the receiving lines, there will be one receiving line in the rectangular area along the x-axis direction. When YLIMIT_h is less than half of the line spacing of the receiving lines, there will be at most one receiving line in the rectangular area along the x-axis direction, and there may be no receiving line. YLIMIT_h must be greater than half of the line spacing of the receiving lines to ensure that there are at least one receiving point of the receiving line in the rectangular area along the x-axis direction. XLIMIT_h is the maximum offset of the current shot data in the x direction for inversion (i.e., the maximum offset used). It is determined by experimental methods based on the characteristics and depth of the near-surface velocity model to be inverted. Taking the maximum offset of the actual acquired data can ensure that all receiving point data of all receiving lines in the rectangular area along the x-axis direction are used for first-arrival tomographic near-surface velocity modeling. Similarly, the larger the value, the higher the accuracy of the tomographic inversion result will be, but the efficiency will be relatively lower. The parameters XLIMIT_v and YLIMIT_v that define the rectangular area along the y-axis direction can be selected based on the observation system. XLIMIT_v must be greater than the trace spacing to ensure that at least 2 receiving points on each receiving line in the rectangular area along the y-axis direction are used for first-arrival tomographic inversion. Similarly, XLIMIT_v must be greater than half of the trace spacing to ensure that at least 1 receiving point on each receiving line in the rectangular area along the y-axis direction is used for first-arrival tomographic inversion. Generally, XLIMIT_v = YLIMIT_h, and YLIMIT_v = XLIMIT_h. When the direction perpendicular to the receiving line is taken as the x-axis direction, the principle is the same. It is only necessary to interchange the meanings represented by XLIMIT_h and YLIMIT_h with those represented by XLIMIT_v and YLIMIT_v.

[0059] Step 2: determine the plane range of the velocity model involved in the forward modeling according to the cross corridor area, including the plane range of the velocity model involved in the forward modeling of the rectangular area along the x-axis direction and the plane range of the velocity model involved in the forward modeling of the rectangular area along the y-axis direction.

[0060] The plane range of the velocity model of the rectangular area along the x-axis direction participating in the forward modeling is the range after the rectangular area along the x-axis direction is extended outward by a given distance DX_LMT and DY_LMT in the x-direction and y-direction respectively.

[0061] The plane range of the velocity model of the rectangular area along the y-axis direction participating in the forward modeling is the range after the rectangular area along the y-axis direction is extended outward by a given distance DX_LMT and DY_LMT in the x-direction and y-direction respectively.

[0062] Generally speaking, for a given distance DX_LMT=DY_LMT=0 extending outward in the x-direction and the y-direction, it is necessary to use DX_LMT>0 and DY_LMT>0 only when there is a very significant lateral change in the near-surface velocity model of the exploration area.

[0063] Step 3, extracting a subset of receiving points in the cross corridor area in the current shot data. According to the cross corridor area, extracting a subset of receiving points belonging to the cross corridor area includes a subset of receiving points in the current shot data located in a rectangular area along the x-axis direction and a subset of receiving points in the rectangular area along the y-axis direction.

[0064] The receiving points in the current shot data that are located in the rectangular area along the x-axis direction constitute the receiving point subset belonging to the rectangular area along the x-axis direction. The receiving points in the current shot data that are located in the rectangular area along the y-axis direction (except for the receiving points that have already appeared in the receiving point subset belonging to the rectangular area along the x-axis direction) constitute the receiving point subset belonging to the rectangular area along the y-axis direction.

[0065] Step 4: From the overall velocity model corresponding to the entire work area, the velocity model within the plane range of the velocity model participating in the forward modeling determined in step 2 is intercepted to form the velocity model participating in the forward modeling, and the ray tracing technology is used to calculate the ray path and travel time from the shot point to each receiving point of the receiving point subset belonging to the cross corridor area extracted in step 3. This is achieved by the following three sub-steps:

[0066] Step 4-1, intercept the velocity model within the plane range of the velocity model participating in the forward modeling in the rectangular area along the x-axis direction determined in step 2, constitute the velocity model participating in the forward modeling, and use ray tracing technology to calculate the ray path and travel time from the shot point to each receiving point in the subset of receiving points belonging to the rectangular area along the x-axis direction extracted in step 3.

[0067] Step 4-2, intercept the velocity model within the plane range of the velocity model participating in the forward modeling in the rectangular area along the y-axis direction determined in step 2, constitute the velocity model participating in the forward modeling, and use ray tracing technology to calculate the ray path and travel time from the shot point to each receiving point in the subset of receiving points belonging to the rectangular area along the y-axis direction extracted in step 3.

[0068] Step 4-3, combining the ray paths and travel times from the shot point to each receiving point obtained in step 4-1 and step 4-2, to obtain the ray paths and travel times from the shot point to each receiving point in the subset of receiving points belonging to the cross corridor area.

[0069] Example 3

[0070] The following is a further detailed description of the above-mentioned method for efficient modeling of first-arrival tomography near-surface velocity:

[0071] ⑴Main parameter input

[0072] The x-axis direction of the local coordinate system of the shot point can be determined either along the receiving line direction or along the direction perpendicular to the receiving line direction.

[0073] The half-side length XLIMIT_h and half-side width YLIMIT_h of the rectangular area along the x-axis direction in the cross corridor area, and the half-side width XLIMIT_v and half-side length YLIMIT_v of the rectangular area along the y-axis direction are input through the parameter input unit.

[0074] The plane range of the velocity model involved in the forward modeling extends outward by the distances DX_LMT and DY_LMT in the x-direction and y-direction.

[0075] ⑵Determine the cross corridor area

[0076] With the shot point as the origin of the local coordinate system and the input shot point coordinate system x-axis direction as the local coordinate system x-axis direction, the shot point and receiving point coordinates of the current shot data are converted into coordinates in the shot point local coordinate system.

[0077] The rectangular area along the x-axis direction is defined according to the half-side length and half-width parameters of the rectangle along the x-axis direction, and the rectangular area along the y-axis direction is defined according to the half-side length and half-width parameters of the rectangle along the y-axis direction. The rectangular area along the x-axis direction and the rectangular area along the y-axis direction together constitute a cross corridor area.

[0078] ⑶ Determine the plane range of the velocity model involved in the forward modeling

[0079] The plane range of the velocity model participating in the forward modeling is determined according to the cross corridor area, including the plane range of the velocity model participating in the forward modeling in the rectangular area along the x-axis direction and the plane range of the velocity model participating in the forward modeling in the rectangular area along the y-axis direction.

[0080] The plane range of the velocity model of the rectangular area along the x-axis direction participating in the forward modeling is the range after the rectangular area along the x-axis direction is extended outward by a given distance DX_LMT and DY_LMT in the x-direction and y-direction respectively.

[0081] The plane range of the velocity model of the rectangular area along the y-axis direction participating in the forward modeling is the range after the rectangular area along the y-axis direction is extended outward by a given distance DX_LMT and DY_LMT in the x-direction and y-direction respectively.

[0082] (4) Extract the receiving point subset belonging to the cross corridor area through the receiving point subset extraction unit

[0083] A subset of receiving points belonging to the cross corridor area is extracted according to the cross corridor area, including a subset of receiving points in the rectangular area along the x-axis direction and a subset of receiving points in the rectangular area along the y-axis direction in the current shot data.

[0084] The receiving points in the current shot data that are located in the rectangular area along the x-axis direction constitute a receiving point subset belonging to the rectangular area along the x-axis direction.

[0085] The receiving points in the current shot data located in the rectangular area along the y-axis direction (excluding the receiving points that have appeared in the receiving point subset belonging to the rectangular area along the x-axis direction) constitute the receiving point subset belonging to the rectangular area along the y-axis direction.

[0086] ⑸ Construct the velocity model involved in the forward modeling through the ray tracing unit and perform ray tracing

[0087] The velocity model in the plane range of the velocity model participating in the forward modeling is intercepted from the overall velocity model corresponding to the entire work area to form the velocity model participating in the forward modeling, and the ray tracing technology is used to calculate the ray path and travel time from the shot point to each receiving point of the receiving point subset belonging to the cross corridor area. It can be decomposed into the following three sub-steps:

[0088] Sub-step 1, intercepting the velocity model within the plane range of the velocity model participating in the forward modeling in the rectangular area along the x-axis direction, forming a velocity model participating in the forward modeling, and using ray tracing technology to calculate the ray path and travel time from the shot point to each receiving point in the receiving point subset belonging to the rectangular area along the x-axis direction.

[0089] Sub-step 2, intercepting the velocity model within the plane range of the velocity model participating in the forward modeling in the rectangular area along the y-axis direction, forming a velocity model participating in the forward modeling, and using ray tracing technology to calculate the ray path and travel time from the shot point to each receiving point in the subset of receiving points belonging to the rectangular area along the y-axis direction.

[0090] Sub-step 3, merging the ray paths and travel times from the shot point to each receiving point obtained in sub-step 1 and sub-step 2 and eliminating duplicate data, to obtain the ray paths and travel times from the shot point to each receiving point in the subset of receiving points belonging to the cross corridor area.

[0091] Example 4

[0092] like Fig.10 A first-arrival tomographic near-surface velocity efficient modeling system is shown, comprising:

[0093] A preset area determination unit: determines the preset area by preset n azimuths and the maximum offset used, wherein n is a natural number ranging from 2 to 8; determines a coordinate system, takes the shot point as the coordinate origin, and selects an x-axis along the receiving line direction or along the direction perpendicular to the receiving line; n is 4, and the azimuth angles are selected from four azimuth angles of 0 degree, 90 degree, 180 degree, and 270 degree; the preset area is composed of a first rectangular area along the receiving line direction and a second rectangular area along the direction perpendicular to the receiving line direction, wherein the width of the first rectangular area is greater than the distance between two adjacent receiving lines; the width of the second rectangular area is greater than the distance between two adjacent receiving points; and the lengths of the first rectangular area and the second rectangular area are the maximum offset used.

[0094] A plane range determination unit for the velocity model involved in the forward modeling is used to determine the plane range of the velocity model involved in the forward modeling according to the preset area;

[0095] A receiving point subset extraction unit: extracting a receiving point subset located in the preset area from the shot data of the current shot point;

[0096] The ray path and travel time calculation unit of the receiving point: constructs the velocity model participating in the forward modeling according to the plane range of the velocity model participating in the forward modeling, that is, the velocity model within the plane range of the velocity model participating in the forward modeling is intercepted from the overall velocity model corresponding to the entire work area to form the velocity model participating in the forward modeling, and then uses the ray tracing technology to calculate the ray path and travel time from the shot point to each receiving point in the receiving point subset.

[0097] Example 5

[0098] An example of a theoretical model. The same first-arrival tomography method and parameters are applied to test the efficiency and accuracy of using receiver data in the cross corridor region.

[0099] Figure 2 The distribution diagram of the shot point and receiving point of the theoretical model of this embodiment is shown in FIG. The receiving line is in the x direction, the receiving point is 30 meters away, and the receiving line is 90 meters away. The shot line is in the y direction, the shot point is 30 meters away, and the shot line is 90 meters away. The minimum distance between the shot point and the receiving line in the y direction is 15 meters, and the minimum distance between the receiving point and the shot line in the x direction is also 15 meters, that is, the shot point and the receiving line do not overlap, and the receiving point and the shot line do not overlap.

[0100] Figure 3The plane distribution diagram of the overall speed model of the entire work area corresponding to the theoretical model of this embodiment. The work area is divided into four speed areas with the center of the work area as the boundary. The upper left and lower right areas are relatively low-speed areas, and the upper right and lower left areas are relatively high-speed areas. There is a 180-meter speed transition zone between each partition to show the lateral change of speed. The figure also shows the positions of the three speed quality control lines, namely AB, CD, and EF. Figure 4 This is an observation system diagram of one of the gun points in this embodiment, that is, a position relationship diagram of a gun point and a corresponding receiving point. The receiving point range corresponding to a gun point includes a rectangular area of ​​2430 meters × 2430 meters, and the gun point is located in the middle.

[0101] Figure 5 For this embodiment Figure 4 The cross corridor area and receiving points of a shot point are selected along the receiving line as the x-axis direction of the shot point local coordinate system. XLIMIT_h=1215 meters, YLIMIT_h=90 meters, XLIMIT_v=YLIMIT_h, YLIMIT_v=XLIMIT_h, DX_LMT=DY_LMT=0. That is, the rectangular area along the x-axis direction that constitutes the cross corridor area will contain all the receiving points of the two receiving lines, and the rectangular area along the y-axis direction will contain the 6 receiving points with the smallest distance between all receiving lines and the shot point in the x-direction.

[0102] Figure 6 The theoretical model of this embodiment corresponds to Figure 3 The velocity profiles of the three velocity quality control lines in (from top to bottom correspond to Figure 3 The spatial variation of the velocity of the theoretical model is shown in the EF, CD, and AB line positions in the figure. By comparing the velocity profiles of the velocity model of the tomographic inversion with the velocity model of the theoretical model at the positions of these three velocity quality control lines, the accuracy of the tomographic inversion can be understood.

[0103] The theoretical model data are respectively subjected to tomographic inversion using all-directional angles (i.e., all-shot azimuths) and full-shot offset data. Figure 5 The data in the cross corridor area shown in the figure are used for tomographic inversion. The same computing platform is used, and the tomographic inversion method and other parameters are exactly the same, and the inversion is iterated 12 times. The results show that if the CPU computing time consumed by tomographic inversion using the data in the cross corridor area is defined as 1 unit, then the CPU computing time consumed by tomographic inversion using the full-angle and full-shot offset data is 11.6 units. It can be seen that the use of data in the cross corridor area for tomographic inversion can significantly improve the processing efficiency.

[0104] Comparing the velocity model of tomographic inversion with the theoretical velocity model, the average absolute error of the velocity model obtained by tomographic inversion using data in the cross corridor area relative to the theoretical velocity model is 0.76% when the depth is less than 100 meters, 1.71% when the depth is less than 200 meters, and 2.30% when the depth is less than 300 meters. The velocity model with this error is accurate enough for most application scenarios of first-arrival tomographic modeling (static correction calculation or prestack depth migration initial velocity model establishment). The accuracy of the velocity model obtained by tomographic inversion using full-angle and full-offset data is higher than that of tomographic inversion using data in the cross corridor area, but the CPU computing time required is increased several times.

[0105] Figure 7 The velocity model corresponding to the full-angle and full-offset data tomographic inversion in this embodiment is Figure 3 The velocity profiles of the three velocity quality control lines (from top to bottom correspond to Figure 3 EF, CD, AB line positions in the diagram). Figure 8 Adopt corresponding Figure 5 The velocity model of the cross corridor area data tomography inversion corresponds to the velocity profiles of the three velocity quality control lines in Figure 3 (from top to bottom, corresponding to Figure 3 The positions of EF, CD, and AB lines in the diagram). Figure 7 and Figure 8 Both Figure 6 There is a good consistency.

[0106] By adopting the first-arrival tomographic near-surface velocity efficient modeling method provided by the present invention, the efficiency of first-arrival tomographic near-surface velocity modeling is significantly improved with a small loss in the accuracy of first-arrival tomographic velocity modeling.

Claims

1. An efficient modeling method for first-arrival tomography near-surface velocity, characterized in that: Includes steps: S10, determining a preset area by using the preset n azimuth angles and the maximum offset used; S20, determining the plane range of the velocity model involved in the forward modeling according to the preset area; S30, extracting a subset of receiving points located in the preset area from the shot data of the current shot point; S40, constructing a velocity model participating in forward modeling according to the plane range of the velocity model participating in forward modeling, and calculating the ray path and travel time from the shot point to each receiving point in the receiving point subset by using ray tracing technology; In the step S10, n is 4, and the preset area is composed of a first rectangular area along the receiving line direction and a second rectangular area along the direction perpendicular to the receiving line; The width of the first rectangular area is greater than the distance between two adjacent receiving lines; the width of the second rectangular area is greater than the distance between two adjacent receiving points; and half of the length of the first rectangular area and the second rectangular area is the maximum offset used.

2. The method for efficient modeling of near-surface velocity of first-arrival tomography according to claim 1, characterized in that: In the step S20, the plane range of the velocity model of the first rectangular area participating in the forward modeling includes a range that is expanded outward by a given distance in the length direction and the width direction of the first rectangular area based on the first rectangular area; the plane range of the velocity model of the second rectangular area participating in the forward modeling includes a range that is expanded outward by a given distance in the width direction and the length direction of the second rectangular area based on the second rectangular area.

3. The method for efficient modeling of near-surface velocity of first-arrival tomography according to claim 1, characterized in that: In the step S30, the receiving point subset includes a receiving point subset formed by superimposing a receiving point subset 1 in the first rectangular area and a receiving point subset 2 in the second rectangular area and removing duplicate data.

4. The method for efficient modeling of near-surface velocity of first-arrival tomography according to claim 1, characterized in that: The step S40 includes: respectively calculating the ray path and travel time from the shot point to each receiving point in the receiving point subset belonging to the first rectangular area and the ray path and travel time from the shot point to each receiving point in the receiving point subset belonging to the second rectangular area and eliminating duplicate data.

5. An efficient modeling system for first-arrival tomography near-surface velocity, comprising: A preset area determination unit: determines the preset area by using the preset n azimuth angles and the maximum offset used; A plane range determination unit for the velocity model involved in the forward modeling is used to determine the plane range of the velocity model involved in the forward modeling according to the preset area; A receiving point subset extraction unit: extracting a receiving point subset located in the preset area from the shot data of the current shot point; A ray path and travel time calculation unit for receiving points: constructs a velocity model participating in forward modeling according to the plane range of the velocity model participating in forward modeling, and calculates the ray path and travel time from the shot point to each receiving point in the receiving point subset by using ray tracing technology; The n is 4, and the preset area is composed of a first rectangular area along the receiving line direction and a second rectangular area along the direction perpendicular to the receiving line; The width of the first rectangular area is greater than the distance between two adjacent receiving lines; the width of the second rectangular area is greater than the distance between two adjacent receiving points; and half of the length of the first rectangular area and the second rectangular area is the maximum offset used.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores at least one computer-executable program, and when the at least one program is executed by the computer, the computer executes the steps of the first-arrival tomographic near-surface velocity efficient modeling method described in any one of claims 1-4.

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