Joint static correction method and system based on tomographic inversion and storage medium

Abstract

The invention provides a joint static correction method and system based on tomographic inversion and a storage medium, and belongs to the technical field of seismic exploration. The method comprises the following steps of: 1, establishing an initial speed model and meshing the speed model; 2, ray path tracking and theoretical travel time calculation; step 3, inversion is carried out to obtain slowness correction; 4, generating a new slowness model; and 5, calculating a static correction value according to the new slowness model. According to the method, the improvement of the simultaneous iterative reconstruction algorithm is provided when the chromatography inversion static correction method is realized, so that the inversion process is stabilized, the long-wavelength static correction value is solved by using chromatography static correction, and meanwhile, the short-wavelength static correction value is solved by using the first-motion wave residual static correction method; a comprehensive application strategy of one-time first arrival pickup and two-time static correction calculation is adopted, the imaging effect of actual seismic data in a complex area can be effectively improved, and the data processing precision is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of seismic exploration, and in particular relates to a combined static correction method, system and storage medium based on tomographic inversion. Background Art

[0002] In seismic exploration, the application research of static correction has always been a hot topic. Elevation static correction does not take low-velocity zones into consideration, and only corrects the elevation difference between the physical point (shot point or receiver point) and the fixed datum. This method is only suitable for areas where there is no low-velocity zone or the low-velocity zone structure does not change laterally. Model static correction refers to a method of obtaining surface low-velocity data of discrete points through conventional low-velocity zone survey methods such as small refraction and micro-logging, interpolating the spatial velocity structure, and calculating the static correction amount; among them, the small refraction method low-velocity zone survey is not applicable to complex surface areas with drastic terrain fluctuations and large changes in surface velocity and depth. The error in fitting the time-distance curve is large, and the obtained results cannot reflect the true structure of the low-velocity zone; the micro-logging method is also not applicable to complex surface areas with drastic terrain fluctuations and large changes in surface velocity and depth. If the measurement points are encrypted, the cost is expensive, the efficiency is low, and the effect is poor. Both refraction statics and tomography statics use the first arrival information of refraction in seismic records to calculate static corrections. Refraction statics have two basic application prerequisites: a stable and continuously traceable refraction interface and moderate lateral velocity changes. Therefore, the refraction statics method is not applicable to complex surface areas with drastic terrain undulations and large surface velocity and depth changes. Tomography statics does not emphasize that the first arrival is a refracted wave, and can calculate both datum statics and residual statics.

[0003] The existing technical methods only consider one static correction quantity, either long wavelength or short wavelength, which is not applicable to complex terrain with drastic surface fluctuations. Summary of the invention

[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a joint static correction method, system and storage medium based on tomographic inversion. The method combines tomographic static correction with the first-arrival wave residual static correction method in complex formations. The comprehensive application can effectively improve the imaging effect of seismic data.

[0005] The present invention is achieved through the following technical solutions:

[0006] A first aspect of the present invention provides a joint static correction method based on tomographic inversion, comprising the following steps:

[0007] The first step is to establish the initial velocity model and mesh the velocity model;

[0008] Step 2: Ray path tracing and theoretical travel time calculation;

[0009] The third step is to invert and obtain the slowness correction value;

[0010] Step 4: Generate a new slowness model;

[0011] Step 5: Calculate the static correction value based on the new slowness model.

[0012] A further improvement of the present invention is:

[0013] In the first step, the initial velocity model is established, specifically:

[0014] The initial velocity model is established based on known regional geological and geophysical information, or using picked first arrivals;

[0015] The geophysical information includes small refraction, micro-well logging and surface outcrop data.

[0016] A further improvement of the present invention is:

[0017] The velocity model is meshed in the first step, specifically:

[0018] The model is divided into a series of rectangular units using a series of grids, and the size of the rectangular units is determined according to the complexity of the surface geological conditions in the study area.

[0019] A further improvement of the present invention is:

[0020] The ray path tracing and theoretical travel time calculation in the second step specifically include:

[0021] 1) Starting from the node where the source point is located, calculate the travel time of all nodes connected to it. The travel time is equal to the distance from the sampling point to the source point divided by the speed corresponding to the grid;

[0022] 2) Find the node with the smallest travel time among all the nodes connected to the source point. The travel time is the ray path from the source point to the node. The ray tracing work of this node is completed, marked as "completed", and used as the new "source point". The travel time is recorded as t s ;

[0023] 3) Calculate the travel time d from the new "source" to all nodes connected to it t , t s +d t The smaller travel time of the node compared with its original travel time is taken as the new travel time of the node;

[0024] 4) Repeat steps 2) and 3) until the new travel time of all nodes is obtained;

[0025] 5) Continue tracing outward in this way until all nodes where the receiving points are located are "completed", and the ray paths and travel times of all the channels of a shot are obtained.

[0026] A further improvement of the present invention is:

[0027] The third step is to invert and obtain the slowness correction value, and the specific operations include:

[0028] For the slowness correction ΔS of any rectangular unit, the following stabilized calculation formula is given:

[0029]

[0030] In the formula, Δt i is the difference between the measured travel time and the theoretical travel time of the ith ray passing through the rectangular unit, L i is the total length of the i-th ray from the shot point to the detector point, Δl i is the length of the i-th ray in the rectangular unit, n is the total number of rays passing through the rectangular unit, and σ 2 is the stabilization factor.

[0031] A further improvement of the present invention is:

[0032] The stabilization factor is calculated according to the As a percentage of the maximum value:

[0033]

[0034] Here ε is a small constant.

[0035] A further improvement of the present invention is:

[0036] In the fourth step, a new slowness model is obtained, and the specific operations include:

[0037] The basic equation for near-surface velocity tomography inversion is the travel time equation along the seismic ray:

[0038]

[0039] Where T is the travel time of the first arrival of the seismic wave, L is the ray path, S(x,z) is the slowness model (the inverse of the velocity) of the underground medium. For a given underground medium slowness model, the ray path is obtained by ray tracing method, and the travel time along the seismic ray is obtained accordingly.

[0040] If a small slowness perturbation is given to the slowness model, the corresponding travel time change is:

[0041]

[0042] Where ΔS(x,z) is the slowness disturbance;

[0043] After discretization, it is written in the following matrix-vector form:

[0044] ΔT=AΔS (5)

[0045] Where, vector ΔT is the residual of the first arrival travel time of the seismic wave, matrix A is the ray path, ΔS is the correction of the slowness model, and the new slowness model is S+ΔS.

[0046] A further improvement of the present invention is:

[0047] The fourth step also includes:

[0048] After obtaining the new slowness model, the ray tracing method is used to obtain the new ray path A, the new travel time and the new residual ΔT, so as to obtain the new correction ΔS. This process is repeated until ||ΔT|| is less than the set error threshold, and the final slowness model is obtained.

[0049] A second aspect of the present invention provides a combined static correction system based on tomographic inversion, comprising:

[0050] Initial model building and meshing unit, used to build initial velocity model and mesh velocity model;

[0051] Computation unit, used for ray path tracing and theoretical travel time calculation;

[0052] A correction value acquisition unit, used for inverting and obtaining the slowness correction value;

[0053] A slowness model generating unit, used for generating a new slowness model;

[0054] The static correction value acquisition unit is used to calculate the static correction value according to the new slowness model.

[0055] According to a third aspect of the present invention, a computer-readable storage medium is provided, wherein 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 in the joint static correction method based on tomographic inversion as described above.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The present invention proposes an improvement on the joint iterative reconstruction algorithm when realizing the tomographic inversion static correction method, so as to stabilize the inversion process. While using tomographic static correction to obtain long-wavelength static correction, the first-arrival residual static correction method is used to obtain short-wavelength static correction. The comprehensive application strategy of picking up the first arrival twice for static correction calculation is adopted, which can effectively improve the imaging effect of actual seismic data in complex areas and improve the accuracy of data processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1Schematic diagram of the process of the joint static correction method based on tomographic inversion in an embodiment of the present invention;

[0059] Figure 2 is the initial velocity model in the embodiment of the present invention;

[0060] Figure 3 is a near-surface velocity model obtained by tomographic inversion in an embodiment of the present invention;

[0061] Figure 4 It is a superimposed section after conventional refraction static correction in an embodiment of the present invention;

[0062] Figure 5 It is a superimposed section after tomographic static correction in an embodiment of the present invention;

[0063] Figure 6 It is a stacked section after the tomographic static correction and the first-arrival residual static correction method are combined and applied in the embodiment of the present invention. DETAILED DESCRIPTION

[0064] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0065] The present invention proposes a joint static correction method based on tomographic inversion, which uses tomographic static correction to obtain long-wavelength static correction and first-arrival residual static correction to obtain short-wavelength static correction. The correction amount of the slowness model is obtained by the simultaneous iterative reconstruction method (SIRT), and the final slowness model is obtained by repeated iterations according to the correction amount, so that the iterative process is stabilized; finally, the actual application effect of the tomographic static correction method is analyzed, and a comprehensive application strategy of long- and short-wavelength static correction is proposed, which effectively solves the static correction problem of actual seismic data in the loess plateau coverage area.

[0066] [Example 1]

[0067] The embodiment of the present invention provides a joint static correction method based on tomographic inversion, such as Figure 1 As shown, the following steps are included:

[0068] The first step is to establish the initial velocity model and mesh the velocity model:

[0069] Initial velocity model: It is established based on known regional geological and geophysical information (such as small refraction, micro-logging and surface outcrop data), or using the picked first arrivals to establish the initial velocity model.

[0070] Velocity model gridding: A series of grids are used to divide the model into a series of rectangular units. The size of the unit is determined according to the complexity of the surface geological conditions in the study area.

[0071] Step 2: Ray path tracing and theoretical travel time calculation:

[0072] Specific operations include:

[0073] 1) Starting from the node where the source point is located, calculate the travel time of all nodes connected to it. The travel time is equal to the distance from the sampling point to the source point divided by the speed corresponding to the grid;

[0074] 2) Find the node with the smallest travel time among all the nodes connected to the source point. The travel time is the ray path from the source point to the node. The ray tracing work of this node is completed, marked as "completed", and used as the new "source point". The travel time is recorded as t s ;

[0075] 3) Calculate the travel time d from the new "source" to all nodes connected to it t , t s +d t The smaller one compared with the original travel time of the node (the original travel time of the node refers to the travel time calculated in 1)) is taken as the new travel time of the node;

[0076] 4) Repeat steps 2) and 3) until the new travel time of all nodes is obtained;

[0077] That is, find the node with the smallest travel time among all nodes (excluding the point marked with "Complete"), get the new "Complete" point and the new "Source Point", and still use t when traveling. s Indicates, go to step 3;

[0078] 5) Continue tracing outward in this way until all nodes where the receiving points are located are "completed", and the ray paths and travel times of all the channels of a shot are obtained.

[0079] The third step is to invert and obtain the slowness correction:

[0080] The simultaneous iterative reconstruction method is used to solve the slowness correction, with good results.

[0081] For the slowness correction ΔS of any rectangular (slowness) unit, the following stabilized calculation formula is given:

[0082]

[0083] Where Δt i is the difference between the measured travel time and the theoretical travel time of the ith ray passing through the rectangular unit, L i is the total length of the i-th ray from the shot point to the detector point, Δl i is the length of the i-th ray in the rectangular unit, n is the total number of rays passing through the rectangular unit, and σ 2 is the stabilization factor;

[0084] First, we need to understand the physical meaning of equation (1), which converts the residual Δt of each ray intoi Weighted distribution to rectangular slowness units, with weight Δl i / L i is the length of the ray segment in the rectangular unit Δl i Corresponding to the total length L of the ray i proportion.

[0085] Secondly, the stabilization factor is calculated according to the As a percentage of the maximum value:

[0086]

[0087] Here, ε is a small constant. This stabilization factor will effectively curb the negative impact of the error in the measured travel time during the model reconstruction process, while controlling the slowness correction in the ray sparse area.

[0088] Step 4: Generate a new slowness model:

[0089] The specific theories applied in the above steps are as follows:

[0090] The basic equation for near-surface velocity tomography inversion is the travel time equation along the seismic ray:

[0091]

[0092] Where T is the travel time of the first arrival of the seismic wave, L is the ray path, and S(x,z) is the slowness (inverse of velocity) model of the underground medium. For a given underground medium slowness model, the ray path can be obtained by ray tracing method, and the travel time along the seismic ray can be obtained accordingly.

[0093] If a small slowness perturbation is given to the slowness model, the corresponding travel time change is:

[0094]

[0095] Where ΔS(x,z) is the slowness disturbance.

[0096] After discretization, it can be written in the following matrix-vector form:

[0097] ΔT=AΔS (5)

[0098] Wherein, vector ΔT is the residual of the first arrival travel time of the seismic wave (measured travel time is subtracted from theoretical travel time, and theoretical travel time is the result of the second step calculation), matrix A is the ray path, ΔS is the correction of the slowness model, and the new slowness model is obtained by using the simultaneous iterative reconstruction method (SIRT).

[0099] Once the new slowness model is obtained, the ray tracing method can be used to obtain the new ray path A, the new travel time and the new residual ΔT, so as to obtain the new correction ΔS. This iteration is repeated until ||ΔT|| is less than the set error threshold, and the final slowness model is obtained.

[0100] That is to say, after obtaining the new slowness model, it is determined whether ||ΔT|| is less than the set error threshold. If so, the next step is to calculate the static correction according to the final slowness model, otherwise it returns to the second step.

[0101] Step 5: Calculate the static correction according to the new slowness model:

[0102] The static correction is equal to the thickness difference from the surface excitation point to a certain point underground divided by the velocity and the thickness difference from the underground point to the surface receiving point divided by the velocity; the velocity here is the reciprocal of the slowness obtained previously.

[0103] The existing conventional methods only consider one type of static correction, either long wavelength or short wavelength; but specifically for the complex loess plateau area, both types need to be considered otherwise the effect is not good; the method of the present invention directly corrects the velocity instead of distinguishing between long wavelength and short wavelength one by one, and its application effect is equivalent to considering the influence of two types of static correction at the same time.

[0104] like Figure 2 As shown, this is the initial velocity model used in this experimental example.

[0105] like Figure 3 As shown in Figure 1, the near-surface velocity model obtained by tomographic inversion in this experimental example is shown in Figure 2. From the near-surface velocity model, it can be seen that the velocity and thickness of the low-velocity reduction zone vary dramatically, and conventional static correction methods encounter difficulties in application.

[0106] like Figure 4 The figure shows the superposition effect of conventional refraction static correction.

[0107] like Figure 5 The figure shows the stacked section after tomographic static correction.

[0108] like Figure 6 As shown, the tomographic inversion static correction method in the embodiment of the present invention successfully solves the serious static correction problem in this area, the continuity of the event axis of the stacked section is good, the wave group characteristics are clear, the signal-to-noise ratio of the main target layer is increased, and the section quality is significantly improved.

[0109] [Example 2]

[0110] The embodiment of the present invention provides a joint static correction system based on tomographic inversion, comprising:

[0111] Initial model building and meshing unit, used to build initial velocity model and mesh velocity model;

[0112] Computation unit, used for ray path tracing and theoretical travel time calculation;

[0113] A correction value acquisition unit, used for inverting and obtaining the slowness correction value;

[0114] A slowness model generating unit, used for generating a new slowness model;

[0115] The static correction value acquisition unit is used to calculate the static correction value according to the new slowness model.

[0116] [Example 3]

[0117] An embodiment of the present invention provides a computer-readable storage medium, which stores at least one computer-executable program. When the at least one program is executed by the computer, the computer executes the steps in the joint static correction method based on tomographic inversion as described above.

[0118] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0119] The above technical solution is only one implementation mode of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A joint static correction method based on tomographic inversion, characterized in that: The following steps are involved: The first step is to establish the initial velocity model and mesh the velocity model; Step 2: Ray path tracing and theoretical travel time calculation; The third step is to invert and obtain the slowness correction value; Step 4: Generate a new slowness model; Step 5: Calculate the static correction value based on the new slowness model.

2. The combined static correction method based on tomographic inversion according to claim 1 is characterized in that: In the first step, the initial velocity model is established, specifically: The initial velocity model is established based on known regional geological and geophysical information, or using the picked first arrivals; the geophysical information includes small refraction, micro-logging and surface outcrop data.

3. The combined static correction method based on tomographic inversion according to claim 1 is characterized in that: The velocity model is meshed in the first step, specifically: The model is divided into a series of rectangular units using a series of grids, and the size of the rectangular units is determined according to the complexity of the surface geological conditions in the study area.

4. The combined static correction method based on tomographic inversion according to claim 1 is characterized in that: The ray path tracing and theoretical travel time calculation in the second step specifically include: 1) Starting from the node where the source point is located, calculate the travel time of all nodes connected to it. The travel time is equal to the distance from the sampling point to the source point divided by the speed corresponding to the grid; 2) Find the node with the smallest travel time among all the nodes connected to the source point. The travel time is the ray path from the source point to the node. The ray tracing work of this node is completed, marked as "completed", and it is used as the new "source point". The travel time is recorded as t s ; 3) Calculate the travel time d from the new "source" to all nodes connected to it t , t s +d t The smaller travel time of the node compared with its original travel time is taken as the new travel time of the node; 4) Repeat steps 2) and 3) until the new travel time of all nodes is obtained; 5) Continue tracing outward in this way until all nodes where the receiving points are located are "completed", and the ray paths and travel times of all the channels of a shot are obtained.

5. The combined static correction method based on tomographic inversion according to claim 4 is characterized in that: The third step is to invert and obtain the slowness correction value, and the specific operations include: For the slowness correction ΔS of any rectangular unit, the following stabilized calculation formula is given: In the formula, Δt i is the difference between the measured travel time and the theoretical travel time of the ith ray passing through the rectangular unit, L i is the total length of the i-th ray from the shot point to the detector point, Δl i is the length of the i-th ray in the rectangular unit, n is the total number of rays passing through the rectangular unit, and σ 2 is the stabilization factor.

6. The combined static correction method based on tomographic inversion according to claim 5 is characterized in that: The stabilization factor is calculated according to the As a percentage of the maximum value: Here ε is a small constant.

7. The combined static correction method based on tomographic inversion according to claim 5 is characterized in that: In the fourth step, a new slowness model is obtained, and the specific operations include: The basic equation for near-surface velocity tomography inversion is the travel time equation along the seismic ray: Where T is the travel time of the first arrival of the seismic wave, L is the ray path, S(x,z) is the slowness model (the inverse of the velocity) of the underground medium. For a given underground medium slowness model, the ray path is obtained by ray tracing method, and the travel time along the seismic ray is obtained accordingly. If a small slowness perturbation is given to the slowness model, the corresponding travel time change is: Where ΔS(x,z) is the slowness disturbance; After discretization, it is written in the following matrix-vector form: ΔT=AΔS (5) Where, vector ΔT is the residual of the first arrival travel time of the seismic wave, matrix A is the ray path, ΔS is the correction of the slowness model, and the new slowness model is S+ΔS.

8. The combined static correction method based on tomographic inversion according to claim 7 is characterized in that: The fourth step also includes: After obtaining the new slowness model, the ray tracing method is used to obtain the new ray path A, the new travel time and the new residual ΔT, so as to obtain the new correction ΔS. This process is repeated until ||ΔT|| is less than the set error threshold, and the final slowness model is obtained.

9. A joint static correction system based on tomographic inversion, characterized in that: include: Initial model building and meshing unit, used to build initial velocity model and mesh velocity model; Computation unit, used for ray path tracing and theoretical travel time calculation; A correction value acquisition unit, used for inverting and obtaining the slowness correction value; A slowness model generating unit, used for generating a new slowness model; The static correction value acquisition unit is used to calculate the static correction value according to the new slowness model.

10. 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 joint static correction method based on tomographic inversion as described in any one of claims 1 to 8.

Images