A method and apparatus for VSP prestack depth migration

Abstract

The application discloses a VSP pre-stack depth migration method and device. The method comprises the following steps: determining a plurality of groups of ray pairs composed of incident rays and reflected rays of the incident rays corresponding to an imaging point on a VSP profile; calculating a formation dip angle of the imaging point according to the ray parameters of the incident rays and the reflected rays of each group of ray pairs; judging whether the ray pair is an effective or ineffective ray pair according to the comparison result of the calculated formation dip angle and the formation dip angle of the corresponding point in the formation dip angle field; and completing the imaging calculation of the imaging point according to the effective ray pairs corresponding to the imaging point. The method constructs the dip angle constraint at each imaging point of the VSP data, thereby limiting the energy of the ray pairs with different structural dip angles participating in the imaging, greatly suppressing the migration drawing arc, and improving the imaging quality of the VSP data.

Description

Technical Field

[0001] This invention relates to the field of seismic data processing technology for petroleum exploration, and particularly to a VSP pre-stack depth migration method and apparatus. Background Technology

[0002] With the deepening of oil and gas exploration research and the current high demand for oil and gas resources, oil and gas exploration and development require methods and technologies that can solve various problems such as fine imaging of complex underground structures and media, reservoir description and dynamic monitoring, and enhanced oil recovery. DAS-VSP observation technology, with its advantages of high precision, high resolution, and short-range detection capabilities, has attracted attention and favor from the oil and gas exploration and development industry.

[0003] DAS-VSP reflection wave imaging mainly includes reflection wave stacking imaging and reflection wave migration imaging. The basic principle of both is to use mathematical algorithms to reverse-propagate the seismic wave field records received in the well and obtain the actual shape of the subsurface structure. The core technology of VSP stacking imaging is the VSP-CDP conversion algorithm, an imaging method based on geometric seismology theory. Before imaging, the specific locations of subsurface reflection interfaces and reflection points are obtained through forward numerical simulation of the seismic wave field. Then, the reflected waves in the seismic record are "transferred" according to the travel times obtained by ray tracing, thus stacking the images. However, conventional VSP-CDP stacking imaging cannot effectively solve the geological task of fine imaging of complex subsurface structures. Therefore, it is necessary to study migration imaging techniques based on reflection waves.

[0004] VSP (Voltage-Spectrum Seismic) reflection migration imaging techniques can be broadly categorized into two types based on their underlying theories: wave equation migration methods and ray migration methods. Wave equation migration algorithms achieve imaging by obtaining numerical solutions to the wave equation and then extending the wavefield. Ray migration algorithms, based on geometric ray theory, perform wavefield extension imaging by obtaining dynamic information about the seismic wavefield and can be broadly classified into Kirchhoff migration methods and beam migration methods. However, for the unique VSP observation system, conventional pre-stack depth migration techniques, whether wave equation or ray migration, leave numerous migration arcs on the migrated profile. This is because, unlike conventional ground seismic acquisition systems, VSP acquisition is an asymmetric system, which hinders the mutual cancellation of migration arcs, resulting in severe noise in the migrated imaging profile and affecting the final image quality. Therefore, suppressing or eliminating these migration arcs caused by the VSP observation system becomes crucial. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a VSP pre-stack depth migration method and apparatus that overcomes or at least partially solves the above problems, greatly suppressing the migration arc, thereby improving the imaging quality of VSP data.

[0006] In a first aspect, embodiments of the present invention provide a VSP pre-stack depth migration method, comprising performing the following steps for imaging points on a VSP profile:

[0007] Identify multiple pairs of rays corresponding to the imaging point, consisting of incident rays and reflected rays of incident rays;

[0008] For each pair of rays, the dip angle of the formation at the imaging point is calculated based on the ray parameters of the incident and reflected rays. The ray pair is determined to be valid or invalid based on the comparison between the calculated dip angle and the dip angle of the corresponding point in the dip angle field. The dip angle field is two-dimensional data obtained in advance based on the seismic profile at the corresponding position of the VSP profile.

[0009] The imaging calculation for the imaging point is completed based on the effective ray pair corresponding to the imaging point.

[0010] Secondly, embodiments of the present invention provide a VSP pre-stack depth migration device, including a ray pair determination module, a ray pair screening module, and an imaging calculation module, which are respectively used to perform the following operations for imaging points on the VSP profile:

[0011] The ray pair determination module is used to determine multiple ray pairs corresponding to the imaging point, consisting of an incident ray and a reflected ray of the incident ray.

[0012] The ray pair screening module is used to calculate the dip angle of the imaging point for each ray pair based on the ray parameters of its incident and reflected rays. Based on the comparison between the calculated dip angle and the dip angle of the corresponding point in the dip angle field, the module determines whether the ray pair is a valid or invalid ray pair. The dip angle field is two-dimensional data obtained in advance based on the seismic profile at the corresponding position of the VSP profile.

[0013] The imaging calculation module is used to perform imaging calculations based on the effective ray pairs corresponding to the imaging points.

[0014] Thirdly, embodiments of the present invention provide a computer program product, including a computer program / instruction, wherein the computer program / instruction, when executed by a processor, implements the above-described VSP pre-stack depth offset method.

[0015] Fourthly, embodiments of this disclosure provide a server, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-described VSP pre-stack depth offset method.

[0016] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0017] The VSP pre-stack depth migration method provided in this invention involves acquiring the structural dip field of the profile from old data of the work area via VSP before performing the VSP pre-stack depth migration. Then, during the migration process, the dip angle value of each pair of imaging rays at the imaging point is calculated, and the ray pairs are screened in conjunction with the pre-extracted structural dip field. Finally, during the migration, structural dip angle constraints are applied to each pair of imaging rays at each imaging point of the VSP data, thereby limiting the energy of ray pairs with different structural dip angles participating in imaging, ultimately achieving the purpose of suppressing the arc drawing of VSP imaging migration, thereby improving the imaging quality of VSP data.

[0018] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0021] Figure 1 This is a flowchart of the VSP pre-stack depth offset method in an embodiment of the present invention;

[0022] Figure 2 for Figure 1 Flowchart illustrating the specific implementation of step S12, which calculates the dip angle of the formation at the imaging point.

[0023] Figure 3 This is a schematic diagram of the coordinate system of the ray center in an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of the local angular characteristics of seismic waves at the imaging point in an embodiment of the present invention;

[0025] Figure 5 for Figure 1 The flowchart of the specific implementation of step S12, which determines whether the ray pair is valid or invalid;

[0026] Figure 6 Comparison of VSP imaging effects in embodiments of the present invention;

[0027] Figure 7 This is a schematic diagram of the VSP pre-stack depth offset device in an embodiment of the present invention. Detailed Implementation

[0028] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] To address the severe arcing phenomenon in VSP reflected wave ray migration imaging in existing technologies, this invention provides a VSP pre-stack depth migration method and apparatus that greatly suppresses migration arcing and achieves high imaging quality for VSP data.

[0032] Example

[0033] This invention provides a VSP pre-stack depth migration method, applicable to both conventional VSP Gaussian beam pre-stack depth migration and DAS-VSP Gaussian beam pre-stack depth migration. The process is as follows: Figure 1 As shown, the following steps are performed on imaging points on the VSP profile:

[0034] Step S11: Determine the multiple sets of ray pairs corresponding to the imaging point, consisting of incident rays and reflected rays of incident rays.

[0035] Step S12: For each pair of rays, calculate the dip angle of the formation at the imaging point based on the ray parameters of its incident and reflected rays. Based on the comparison between the calculated dip angle and the dip angle of the corresponding point in the formation dip angle field, determine whether the ray pair is a valid or invalid ray pair.

[0036] The stratigraphic dip field is a two-dimensional array obtained in advance based on the seismic profiles at the corresponding locations of the VSP profile.

[0037] VSP acquisition areas typically have old data. The dip angle of the strata can be extracted from the seismic profile at the corresponding location of the VSP profile using plane wave decomposition technology, thus obtaining the strata dip field.

[0038] Assume there are n seismic traces along the main survey line of an old profile. x The number of sampling points is n. z Then the old data profile can be represented as Sur_image(n x n z A two-dimensional array of ) can be used to obtain the corresponding formation dip field Sur_dip(n) through techniques such as plane wave decomposition. x n z A two-dimensional array of ).

[0039] The above-mentioned ray parameters can be the velocity vectors of the incident ray and the reflected ray.

[0040] In some embodiments, the dip angle of the formation at the imaging point is calculated, with reference to... Figure 2 As shown, the following steps may be included:

[0041] Step S1211: Take the sum of the velocity vectors of the incident ray and the reflected ray as the tilt vector.

[0042] Solving for the ray parameter Ps at any point n on the incident ray beam using a Gaussian ray beam. In the three-dimensional ray center coordinate system ( Figure 3 The travel time at any point n on and around the ray can be approximated using Taylor expansion as follows:

[0043]

[0044] In formula (1), T(m) is the real travel time from the source point to the reference point m on the central ray, and q T =(q I ,q J Let M(m) be a two-dimensional vector describing the position of point n in the ray intersection coordinate system. M(m) is the second-order partial derivative during travel, which is a scalar in the two-dimensional medium. Assume... Then equation (1) and its spatial partial derivatives are:

[0045]

[0046]

[0047] Therefore, the ray slowness vector at point n is obtained as:

[0048]

[0049] Finally, the unit vector, i.e., the ray parameters, at point n on the Gaussian beam can be obtained:

[0050] P(n)=v(n)(P1,P2,P3) (5)

[0051] That is, the ray parameters are represented by velocity vectors. The ray parameters of point n on the incident Gaussian ray beam are labeled as Ps.

[0052] Similarly, the ray parameter Pr of point n on the reflected ray beam is solved based on the Gaussian ray beam.

[0053] like Figure 4 As shown, in the three-dimensional case, the incident ray parameter Ps and the reflected ray parameter Pr together describe the wave propagation direction characteristics at the imaging point m. The sum of the incident and reflected ray parameters Pm is called the illumination vector or tilt vector.

[0054] Step S1212: Calculate the dip angle of the formation at the imaging point based on the dip vector.

[0055] According to the rules of vector operation, further, based on the dip angle vector, the dip angle of the formation at the imaging point is calculated using the following formula (6):

[0056]

[0057] In formula (6), m x m z Let m be the spatial coordinates of the imaging point, and z be the unit vector along the Z-axis. Dip_ray(m) x ,m z P represents the dip angle of the formation at imaging point m. m Let P be the tilt vector of the imaging point m. mz Let be the component of the tilt vector of the imaging point m in the Z-axis direction.

[0058] Reference Figure 5 As shown, determining whether a ray pair is valid or invalid can specifically include the following steps:

[0059] Step S1221: Determine whether the difference between the calculated formation dip angle and the corresponding point in the formation dip angle field meets the allowable error of the formation dip angle at the imaging point.

[0060] That is, to determine whether the absolute value of the difference between the calculated dip angle of the formation and the dip angle of the corresponding point in the dip angle field is less than the allowable error of the dip angle of the formation at the imaging point.

[0061] If yes, proceed to step S1222; otherwise, proceed to step S1223.

[0062] Step S1222: Determine that the ray pair is a valid ray pair.

[0063] Step S1223: Determine that the ray pair is an invalid ray pair.

[0064] The permissible error of the stratigraphic dip angle at the imaging point can be determined in the following two ways:

[0065] (1) Determine the depth influence coefficient of the formation dip angle based on the location of the imaging point; determine the allowable error of the formation dip angle of the imaging point based on the set dip angle constraint threshold and the depth influence coefficient.

[0066] The depth influence coefficient of the formation dip angle at the imaging point is determined by the following formula (7):

[0067]

[0068] In formula (7), α m The depth influence coefficient of the dip angle of the strata at imaging point m, max D d is the maximum depth of the VSP profile. m Let m be the depth of the imaging point.

[0069] Based on the set dip angle constraint threshold and depth influence coefficient, the allowable error of the formation dip angle of the imaging point is determined by the following formula (8):

[0070] ΔDip m =Dip_range*(0.5+α) m (8)

[0071] In formula (8), ΔDip m The allowable error for the dip angle of the formation at imaging point m is given by α, where Dip_range is the set dip angle constraint threshold. m The depth influence coefficient is the dip angle of the stratum at imaging point m.

[0072] (2) Determine the permissible error of the dip angle of the imaging point based on the predetermined relationship between the depth and the permissible error of the dip angle of the stratum.

[0073] The relationship between depth and the allowable error of the dip angle of the strata is predetermined by the following formula (9):

[0074]

[0075] In formula (9), ΔDip d Here, represents the allowable error for the dip angle of the formation at depth d, where Dip_range is the set dip angle constraint threshold, and max... D This represents the maximum depth of the VSP profile.

[0076] The tilt angle constraint threshold Dip_range mentioned above needs to be tested during the specific offset process, and is generally set to 10° by default.

[0077] Step S13: Complete the imaging calculation of the imaging point based on the effective ray pair corresponding to the imaging point.

[0078] The VSP pre-stack depth migration method provided in this invention involves acquiring the structural dip field of the profile from old data of the work area via VSP before performing the VSP pre-stack depth migration. Then, during the migration process, the dip angle value of each pair of imaging rays at the imaging point is calculated, and the ray pairs are screened in conjunction with the pre-extracted structural dip field. Finally, during the migration, structural dip angle constraints are applied to each pair of imaging rays at each imaging point of the VSP data, thereby limiting the energy of ray pairs with different structural dip angles participating in imaging, ultimately achieving the purpose of suppressing the arc drawing of VSP imaging migration, thereby improving the imaging quality of VSP data.

[0079] See Figure 6 As shown, Figure 6 The left side of the image shows the migration result using the conventional method, the middle side shows the picked structural dip field, and the right side shows the migration result of the embodiment of this invention. It can be seen that the embodiment of this invention effectively solves the problem of arc drawing in VSP imaging migration, resulting in higher imaging quality and a better match with the formation dip field.

[0080] Based on the inventive concept of this invention, embodiments of this invention also provide a VSP pre-stack depth offset device, the structure of which is as follows: Figure 7 As shown, it includes a ray pair determination module 71, a ray pair screening module 72, and an imaging calculation module 73, which are respectively used to perform the following operations on the imaging points on the VSP profile:

[0081] The ray pair determination module 71 is used to determine multiple ray pairs corresponding to the imaging point, which consist of incident rays and reflected rays of incident rays.

[0082] The ray pair screening module 72 is used to calculate the dip angle of the imaging point for each ray pair based on the ray parameters of its incident and reflected rays. Based on the comparison between the calculated dip angle and the dip angle of the corresponding point in the dip angle field, it determines whether the ray pair is a valid or invalid ray pair. The dip angle field is two-dimensional data obtained in advance based on the seismic profile at the corresponding position of the VSP profile.

[0083] The imaging calculation module 73 is used to perform imaging calculations for the imaging point based on the effective ray pairs corresponding to the imaging point.

[0084] In some embodiments, the ray pair screening module 72, which calculates the dip angle of the imaging point based on the ray parameters of its incident and reflected rays, is specifically used for:

[0085] The sum of the velocity vectors of the incident and reflected rays is used as the dip vector; the dip angle of the formation at the imaging point is calculated based on the dip vector.

[0086] In some embodiments, the ray pair screening module 72 calculates the formation dip angle of the imaging point based on the dip angle vector, specifically for:

[0087] Based on the dip angle vector, the formation dip angle of the imaging point is calculated using the following formula:

[0088]

[0089] In the above formula, m x m z Let m be the spatial coordinates of the imaging point, and z be the unit vector along the Z-axis. Dip_ray(m) x ,m z P represents the dip angle of the formation at imaging point m. m Let P be the tilt vector of the imaging point m. mz Let be the component of the tilt vector of the imaging point m in the Z-axis direction.

[0090] In some embodiments, the ray pair screening module 72, which determines whether a ray pair is valid or invalid based on the comparison between the calculated formation dip angle and the corresponding point's formation dip angle in the formation dip angle field, is specifically used for:

[0091] Determine whether the difference between the calculated formation dip angle and the corresponding point in the formation dip angle field meets the allowable error of the formation dip angle at the imaging point; if yes, determine that the ray pair is a valid ray pair; if no, determine that the ray pair is an invalid ray pair.

[0092] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0093] Based on the inventive concept of the present invention, embodiments of the present invention also provide a computer program product, including a computer program / instruction, wherein the computer program / instruction implements the above-described VSP pre-stack depth offset method when executed by a processor.

[0094] Based on the inventive concept of this invention, this embodiment of the invention also provides a server, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-described VSP pre-stack depth offset method.

[0095] Unless otherwise specifically stated, terms such as processing, calculation, operation, determination, display, etc., may refer to the actions and / or processes of one or more processing or computing systems or similar devices that represent the manipulation and conversion of data representing physical (e.g., electronic) quantities within the registers or memory of the processing system into other data similarly representing physical quantities within the memory, registers, or other such information storage, transmission, or display devices of the processing system. Information and signals can be represented using any of a variety of different techniques and methods. For example, data, instructions, commands, information, signals, bits, symbols, and chips mentioned throughout the above description can be represented by voltage, current, electromagnetic waves, magnetic fields or particles, light fields or particles, or any combination thereof.

[0096] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process may be rearranged without departing from the scope of this disclosure. The appended method claims provide elements of various steps in an exemplary order and are not intended to limit the scope to the specific order or hierarchy described.

[0097] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of the invention.

[0098] Those skilled in the art will also understand that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments herein can be implemented as electronic hardware, computer software, or a combination thereof. To clearly illustrate the interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps described above are generally described in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art can implement the described functionality in alternative ways for each specific application; however, such implementation decisions should not be construed as departing from the scope of this disclosure.

[0099] The steps of the methods or algorithms described in conjunction with the embodiments herein can be directly embodied in hardware, software modules executed by a processor, or a combination thereof. The software modules can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium well known in the art. An exemplary storage medium is connected to the processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. The ASIC can reside in a user terminal. Alternatively, the processor and storage medium can exist as discrete components in the user terminal.

[0100] For software implementation, the techniques described in this application can be implemented using modules (e.g., procedures, functions, etc.) that perform the functions described in this application. This software code can be stored in memory units and executed by a processor. The memory units can be implemented within the processor or outside the processor; in the latter case, they are communicatively coupled to the processor via various means, as is well known in the art.

[0101] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as interpreted when used as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

Claims

1. A VSP pre-stack depth migration method, characterized in that, This includes performing the following steps for imaging points on the VSP profile: Identify multiple pairs of rays corresponding to the imaging point, consisting of incident rays and reflected rays of incident rays; For each pair of rays, the dip angle of the formation at the imaging point is calculated based on the ray parameters of its incident and reflected rays. It is then determined whether the difference between the calculated dip angle and the dip angle of the corresponding point in the dip angle field meets the allowable error of the dip angle of the imaging point. If yes, the ray pair is determined to be a valid ray pair; otherwise, it is determined to be an invalid ray pair. The dip angle field is a two-dimensional array obtained in advance based on the seismic profile at the corresponding position of the VSP profile. The imaging calculation for the imaging point is completed based on the effective ray pair corresponding to the imaging point.

2. The method as described in claim 1, characterized in that, The calculation of the stratigraphic dip angle of the imaging point based on the ray parameters of the incident and reflected rays specifically includes: The sum of the velocity vectors of the incident ray and the reflected ray is taken as the tilt vector; The dip angle of the formation at the imaging point is calculated based on the dip angle vector.

3. The method as described in claim 2, characterized in that, The calculation of the formation dip angle of the imaging point based on the dip angle vector specifically includes: Based on the dip angle vector, the dip angle of the formation at the imaging point is calculated using the following formula (1): （1）； In formula (1), m x m z Let m be the spatial coordinates of the imaging point, and z be the unit vector along the Z-axis. Let m be the dip angle of the strata at imaging point m. Let m be the tilt vector of the imaging point. Let be the component of the tilt vector of the imaging point m in the Z-axis direction.

4. The method as described in claim 1, characterized in that, The permissible error of the formation dip angle at the imaging point is obtained in the following manner: The depth influence coefficient of the stratum dip angle is determined based on the location of the imaging point; The allowable error of the formation dip angle at the imaging point is determined based on the set dip angle constraint threshold and the depth influence coefficient.

5. The method as described in claim 4, characterized in that, The depth influence coefficient for determining the dip angle of the strata based on the location of the imaging point specifically includes: The depth influence coefficient of the formation dip angle at the imaging point is determined by the following formula (2): （2）； In formula (2), Let m be the depth influence coefficient of the stratum dip angle at imaging point m. The maximum depth of the VSP profile. Let m be the depth of the imaging point.

6. The method as described in claim 4, characterized in that, The step of determining the allowable error of the formation dip angle of the imaging point based on the set dip angle constraint threshold and the depth influence coefficient specifically includes: Based on the set dip angle constraint threshold and the depth influence coefficient, the allowable error of the formation dip angle of the imaging point is determined by the following formula (3): （3）； In formula (3), Let m be the allowable error of the dip angle of the formation at imaging point m. The set tilt angle constraint threshold, is the depth influence coefficient of the dip angle of the stratum at imaging point m.

7. The method as described in claim 1, characterized in that, The permissible error of the formation dip angle at the imaging point is obtained in the following manner: The permissible error of the formation dip angle at the imaging point is determined based on the predetermined relationship between the depth and the permissible error of the formation dip angle.

8. The method as described in claim 7, characterized in that, The relationship between the depth and the allowable error of the dip angle is predetermined by the following formula (4): （4）； In formula (4), Let d be the allowable error for the dip angle of the formation at depth d. The set tilt angle constraint threshold, The maximum depth of the VSP profile.

9. The method according to any one of claims 1 to 8, characterized in that, The dip field of the strata is obtained from the seismic profile at the corresponding location of the VSP profile, specifically including: By using plane wave decomposition technology, the dip angle of the strata is extracted from the seismic profile at the corresponding position of the VSP profile to obtain the strata dip angle field.

10. A VSP pre-stack depth offset device, characterized in that, It includes a ray pair determination module, a ray pair screening module, and an imaging calculation module, which are used to perform the following operations on imaging points on the VSP profile: The ray pair determination module is used to determine multiple ray pairs corresponding to the imaging point, which consist of incident rays and reflected rays of incident rays. The ray pair screening module is used to calculate the dip angle of the formation at the imaging point for each ray pair based on the ray parameters of its incident and reflected rays; determine whether the difference between the calculated dip angle and the dip angle of the corresponding point in the dip angle field meets the allowable error of the dip angle of the imaging point; if yes, the ray pair is determined to be a valid ray pair; if no, the ray pair is determined to be an invalid ray pair; the dip angle field is two-dimensional data obtained in advance based on the seismic profile at the corresponding position of the VSP profile; The imaging calculation module is used to perform imaging calculations for the imaging points based on the effective ray pairs corresponding to the imaging points.

11. A computer program product, comprising a computer program / instructions, characterized in that, When the computer program / instruction is executed by the processor, it implements the VSP pre-stack depth offset method as described in any one of claims 1 to 9.

12. A server, characterized in that, include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the program, implements the VSP pre-stack depth migration method according to any one of claims 1 to 9.

Images