Offset speed determination method and device and terminal

Abstract

The embodiment of the invention discloses a migration speed determination method and device and a terminal, and belongs to the field of seismic data processing. The method comprises the following steps: for imaging points in a first stratum, carrying out pre-stack depth migration on seismic data of the imaging points to obtain a plurality of first common imaging point gathers; under the condition that the straightness of the event of each first common imaging point gather is not less than the preset straightness, interpolating the plurality of first offset speeds to obtain a plurality of second offset speeds; for any second migration velocity, generating a second common imaging point gather based on the first target common imaging point gather; and determining a target second migration speed from the plurality of second migration speeds, and determining the target second migration speed as the migration speed of the first stratum. According to the scheme, pre-stack depth migration does not need to be carried out on the seismic data according to each second migration speed, the calculation amount of generating the second common imaging point gather is remarkably reduced, and the efficiency of determining the migration speed is improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of seismic data processing, and in particular to a method, device and terminal for determining an offset velocity. Background Art

[0002] In the field of seismic data processing, migration imaging is an important seismic data processing technology. Migration imaging refers to the migration of seismic data reflected by the formation according to the migration velocity of the formation to obtain a seismic image that can reflect the formation structure. Therefore, how to accurately determine the migration velocity of the formation to generate a seismic image is a technical problem that needs to be solved.

[0003] In the related art, for any stratum, a velocity enumeration method is usually used to generate multiple offset velocities of the stratum. Then, according to each offset velocity, the seismic data is subjected to a depth prestack migration (a depth domain offset imaging technology) to obtain a seismic image corresponding to each offset velocity. Then, according to the straightness of the event axis displayed by the seismic image, the offset velocity corresponding to the seismic image with a relatively straight event axis is taken as the offset velocity of the stratum.

[0004] However, the above method requires multiple deep prestack migrations for each stratum. In addition, if there is no seismic image with a relatively straight event axis, multiple new migration velocities need to be re-enumerated. The deep prestack migration is then performed based on the new migration velocities, which requires a large amount of calculation and has a low efficiency in determining the migration velocity. Summary of the invention

[0005] The embodiment of the present application provides a method, device and terminal for determining migration velocity, which eliminates the need to perform prestack depth migration on seismic data according to each migration velocity, significantly reduces the amount of calculation for generating common imaging point gathers, and improves the efficiency of determining migration velocity. The technical solution is as follows:

[0006] In one aspect, a method for determining an offset velocity is provided, the method comprising:

[0007] For imaging points in the first stratum, prestack depth migration is performed on seismic data of the imaging points to obtain a plurality of first common imaging point gathers, where the first common imaging point gathers are used to represent amplitude values ​​of the seismic data at different depths underground;

[0008] When the straightness of the event axis of each first common imaging point gather is not less than a preset straightness, a plurality of first migration velocities are interpolated respectively to obtain a plurality of second migration velocities, wherein the first migration velocities are used to perform prestack depth migration on the seismic data of the imaging point;

[0009] For any second migration velocity, based on the first target common imaging point gather, a second common imaging point gather is generated, wherein the first target common imaging point gather is a first common imaging point gather generated by a target first migration velocity, the target first migration velocity is a first migration velocity having a minimum difference with the second migration velocity among the plurality of first migration velocities, and the second common imaging point gather is used to reflect a result of prestack depth migration of seismic data of the imaging point by the second migration velocity;

[0010] A target second offset velocity is determined from the plurality of second offset velocities, the target second offset velocity is determined as the offset velocity of the first formation, and the straightness of the event axis of the second common imaging point gather generated by the target second offset velocity is less than the preset straightness.

[0011] In another aspect, a device for determining an offset speed is provided, the device comprising:

[0012] A migration module, for performing prestack depth migration on seismic data of imaging points in a first stratum to obtain a plurality of first common imaging point gathers, wherein the first common imaging point gathers are used to represent amplitude values ​​of the seismic data at different depths underground;

[0013] An interpolation module, configured to interpolate a plurality of first migration velocities respectively to obtain a plurality of second migration velocities when the straightness of the event axis of each first common imaging point gather is not less than a preset straightness, wherein the first migration velocities are used to perform prestack depth migration on the seismic data of the imaging point;

[0014] A first generating module is configured to generate a second common imaging point gather based on a first target common imaging point gather for any second migration velocity, wherein the first target common imaging point gather is a first common imaging point gather generated by a target first migration velocity, the target first migration velocity is a first migration velocity having a minimum difference with the second migration velocity among the plurality of first migration velocities, and the second common imaging point gather is used to reflect a result of prestack depth migration of seismic data of the imaging point by the second migration velocity;

[0015] The first determination module is configured to determine a target second offset velocity from the plurality of second offset velocities, determine the target second offset velocity as the offset velocity of the first formation, and the straightness of the event axis of the second common imaging point gather generated by the target second offset velocity is less than the preset straightness.

[0016] In some embodiments, the second common imaging point gather is used to represent the amplitude value of the seismic data at a first depth, where the first depth is the depth of the location of the imaging point; the first generating module includes:

[0017] an acquisition unit, configured to acquire the travel time and target position of a first ray, wherein the first ray is a ray emitted toward the surface at a preset emission angle at the location of the imaging point, the travel time is the time taken for the first ray to be emitted from the surface, and the target position is the position where the first ray is emitted from the surface;

[0018] a first determining unit, configured to, in response to a successful emission of a second ray, count down based on the travel time, and determine a depth reached by the second ray when the travel time is exhausted as a second depth, wherein the second ray is a ray emitted underground at the target position;

[0019] A second determining unit, configured to determine an amplitude value of the seismic data at the second depth based on the first target common imaging point gather;

[0020] The third determining unit is configured to use the amplitude value of the seismic data at the second depth as the amplitude value of the seismic data at the first depth.

[0021] In some embodiments, the acquisition unit is used to acquire the initial offset velocity of each formation; based on the preset exit angle and the transmission velocity of the first ray in each formation, the incident angle and the exit angle of the first ray at each formation interface are determined by the law of refraction, and the transmission velocity of the first ray in each formation is the initial offset velocity of each formation; based on the transmission velocity of the first ray in each formation, the incident angle and the exit angle of the first ray at each formation interface and the first depth, the travel time of the first ray and the target position are determined.

[0022] In some embodiments, the second determination unit is used to, when there is a depth sampling point at the second depth in the first target common imaging point gather, use the amplitude value of the depth sampling point as the amplitude value of the seismic data at the second depth; and when there is or is not a depth sampling point at the second depth in the first target common imaging point gather, interpolate the amplitude value of at least one adjacent depth sampling point at the second depth to obtain the amplitude value of the seismic data at the second depth.

[0023] In some embodiments, the apparatus further comprises:

[0024] An acquisition module, used for acquiring an initial velocity model, wherein the initial velocity model is used for representing the relationship between the depth of a formation and an initial migration velocity of the formation;

[0025] A second determination module, configured to determine an initial migration velocity of the first formation based on the initial velocity model;

[0026] The second generating module is used to generate the plurality of first offset speeds within a preset speed range based on the initial offset speed and according to a generating step length, wherein the generating step length is used to represent a difference between two adjacent first offset speeds.

[0027] In some embodiments, the apparatus further comprises:

[0028] An analysis module, configured to perform time domain velocity analysis on the seismic data of the imaging point to obtain a time domain velocity field, wherein the time domain velocity field is used to represent the relationship between the transmission time of the seismic data in each stratum and the offset velocity of each stratum;

[0029] The migration module is further used to perform pre-stack time migration on the seismic data of the imaging point to obtain a time domain migration profile, and the time domain migration profile is used to divide multiple underground strata and determine the depth of each stratum;

[0030] A construction module is used to construct the initial velocity model based on the time domain velocity field and the time domain migration profile.

[0031] In some embodiments, the interpolation module is used to determine a second target common imaging point gather when the straightness of the event axis of each of the first common imaging point gathers is not less than the preset straightness, the second target common imaging point gather being the first common imaging point gather having the smallest difference between the straightness of the event axis and the preset straightness; determine a third offset speed based on the second target common imaging point gather, the third offset speed being the first offset speed for generating the second target common imaging point gather; and interpolate the third offset speed within a preset speed range according to an interpolation interval to obtain the multiple second offset speeds.

[0032] In some embodiments, the apparatus further comprises:

[0033] The third determination module is configured to determine the migration velocity of the second formation based on a plurality of common imaging point gathers of imaging points in the second formation in response to obtaining the migration velocity of the first formation, where the second formation is a layer below the first formation.

[0034] On the other hand, a terminal is provided, the terminal comprising a processor and a memory, the memory storing at least one computer program, the at least one computer program being loaded and executed by the processor to implement the offset speed determination method as described in the above aspect.

[0035] On the other hand, a computer-readable storage medium is provided, wherein at least one computer program is stored in the computer-readable storage medium, and the at least one computer program is loaded and executed by a processor to implement the offset velocity determination method as described in the above aspect.

[0036] On the other hand, a computer program product is provided, comprising a computer program, wherein the computer program is loaded and executed by a processor to implement the offset velocity determination method as described in the above aspects.

[0037] The embodiment of the present application provides a scheme for determining the migration velocity. In the process of determining the migration velocity of the first formation, firstly, the seismic data of the imaging points in the first formation are pre-stacked depth migrated according to the multiple first migration velocities to obtain multiple first common imaging point gathers. Since the straighter the event axis of the common imaging point gather, the better the imaging effect of the common imaging point gather and the higher the reliability. Therefore, the migration velocity corresponding to the first common imaging point gather whose event axis straightness is less than the preset straightness can be determined as the migration velocity of the first formation. In the case where the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, it indicates that the reliability of the above multiple migration velocities is low and none of them can be used as the migration velocity of the first formation. Then, the multiple first migration velocities are interpolated respectively to obtain multiple second migration velocities. For each second migration velocity, a second common imaging point gather is generated according to the first common imaging point gather corresponding to the first migration velocity with the smallest difference therewith. Then, the migration velocity corresponding to the second common imaging point gather whose event axis is relatively straight is used as the migration velocity of the first layer. By adopting the above method, it is no longer necessary to perform prestack depth migration on seismic data according to each second migration velocity, which significantly reduces the amount of calculation for generating the second common imaging point gathers and improves the efficiency of determining the migration velocity. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 It is a schematic diagram of an implementation environment provided by an embodiment of the present application;

[0040] Figure 2 is a flow chart of a method for determining an offset velocity provided in an embodiment of the present application;

[0041] Figure 3 is a flow chart of another method for determining an offset velocity provided in an embodiment of the present application;

[0042] Figure 4 is a flow chart for determining an offset speed provided in an embodiment of the present application;

[0043] Figure 5It is a schematic diagram of imaging shallow low signal-to-noise ratio seismic data provided by an embodiment of the present application;

[0044] Figure 6 is a schematic diagram of a horizontal layered model provided in an embodiment of the present application;

[0045] Figure 7 is a schematic diagram of an imaging effect provided by an embodiment of the present application;

[0046] Figure 8 is a schematic diagram of an actual underground model provided in an embodiment of the present application;

[0047] Fig. 9 is a schematic diagram of another imaging effect provided by an embodiment of the present application;

[0048] Fig.10 is a schematic diagram of another imaging effect provided by an embodiment of the present application;

[0049] Fig.11 is a structural schematic diagram of a device for determining an offset velocity provided in an embodiment of the present application;

[0050] Fig.12 is a schematic structural diagram of another device for determining a displacement velocity provided in an embodiment of the present application;

[0051] Fig.13 It is a structural diagram of a terminal provided in an embodiment of the present application. DETAILED DESCRIPTION

[0052] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the implementation methods of the present application will be further described in detail below in conjunction with the accompanying drawings.

[0053] It is understood that the terms "first", "second", etc. used in this application can be used in this article to describe various concepts, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of this application, the first common imaging point gather can be called the second common imaging point gather, and similarly, the second common imaging point gather can be called the first common imaging point gather.

[0054] It should be noted that the information (including but not limited to user device information, user personal information, etc.), data (including but not limited to data used for analysis, stored data, displayed data, etc.) and signals involved in this application are all authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant laws, regulations and standards of relevant countries and regions. For example, the earthquake data involved in this application was obtained with full authorization.

[0055] The implementation environment of the embodiments of the present application is introduced below.

[0056] Figure 1 is a schematic diagram of an implementation environment provided by an embodiment of the present application, see Figure 1 , the implementation environment includes: a terminal 101 and a server 102. The terminal 101 can be connected to the server 102 via a wireless network or a wired network.

[0057] Optionally, the terminal 101 can be at least one of a smart phone, a desktop computer, a laptop computer and a portable computer. An application can be installed and run on the terminal 101, and the application is used to perform various migration imaging processes on the seismic data of the imaging points in the formation, such as pre-stack depth migration, post-stack depth migration, pre-stack time migration and post-stack time migration. The user can log in to the application through the terminal 101, and perform pre-stack depth migration on the above seismic data through the application to obtain the common imaging point gather of the imaging point. The user can also view the straightness of the event axis of the common imaging point gather through the application. The application is associated with the server 102, and the server 102 provides background services.

[0058] Optionally, the server 102 is an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communications, middleware services, domain name services, security services, CDN (Content Delivery Network), and big data and artificial intelligence platforms. In some embodiments, the server 102 undertakes the main computing work, and the terminal 101 undertakes the secondary computing work; or, the server 102 undertakes the secondary computing work, and the terminal 101 undertakes the main computing work; or, the server 102 and the terminal 101 use a distributed computing architecture for collaborative computing.

[0059] Terminal 101 may generally refer to one of multiple terminals. This embodiment is illustrated by taking terminal 101 as an example. Those skilled in the art may know that the number of the above terminals may be more or less. For example, the above terminals may be several, or the above terminals may be dozens or hundreds, or more. The embodiment of the present application does not limit the number and device type of the terminals.

[0060] Figure 2 is a flow chart of a method for determining an offset speed provided in an embodiment of the present application. The embodiment of the present application is performed by a terminal as an example. Figure 2 , the method comprising:

[0061] 201. For imaging points in a first stratum, the terminal performs pre-stack depth migration on seismic data of the imaging points to obtain a plurality of first common imaging point gathers, where the first common imaging point gathers are used to represent amplitude values ​​of seismic data at different depths underground.

[0062] In the embodiment of the present application, the first stratum is any stratum to be detected underground. The imaging point is a point in the first stratum that can reflect seismic data. The first stratum includes at least one imaging point. The embodiment of the present application is described by taking an imaging point of the first stratum as an example. After the seismic wave is successfully excited from the blast point on the surface to any direction underground, the seismic wave propagates in multiple strata to be detected underground. During the propagation process, the seismic wave can be reflected to the surface by the imaging point in the stratum. Accordingly, the terminal can collect the seismic wave reflected by the imaging point through multiple detectors on the surface, that is, collect the seismic data reflected by the imaging point. Among them, the seismic data collected by a detector is called a seismic trace. The seismic trace records multiple seismic data collected by the corresponding detector.

[0063] The terminal performs prestack depth migration on the collected seismic data according to multiple first migration speeds, and obtains multiple first common imaging point gathers. The gather is a collection of multiple seismic traces. The first common imaging point gather refers to a gather obtained by sorting the seismic data reflected from the same imaging point underground according to the shot offset (the distance between the shot point and the detection point). The terminal can determine the amplitude values ​​of the above seismic data at different depths underground through the first common imaging point gather.

[0064] 202. When the straightness of the event axis of each first common imaging point gather is not less than a preset straightness, the terminal interpolates a plurality of first migration velocities to obtain a plurality of second migration velocities, wherein the first migration velocities are used to perform prestack depth migration on the seismic data of the imaging point.

[0065] In the embodiment of the present application, the event axis of the first common imaging point gather refers to the line connecting the extreme values ​​(commonly known as peaks or troughs) of the same vibration phase of the seismic data in each seismic channel. Therefore, in the first common imaging point gather, the terminal determines the maximum amplitude value or the minimum amplitude value of the seismic data recorded in each seismic channel. Then the terminal connects the maximum amplitude values ​​recorded in each seismic channel, or connects the minimum amplitude values ​​recorded in each seismic channel, to obtain the event axis of the first common imaging point gather and the straightness of the event axis. The terminal can determine the imaging effect of the first common imaging point gather through the straightness of the event axis. The straighter the event axis, the better the imaging effect of the common imaging point gather and the higher the reliability. When the straightness of the event axis is not less than the preset straightness, it indicates that the event axis is relatively curved; when the straightness of the event axis is less than the preset straightness, it indicates that the event axis is relatively straight. Among them, the preset straightness can be a preset angle, such as 10°, 15° or 20°, which is not limited in the embodiment of the present application. Therefore, the terminal can determine the first common imaging point gather whose flatness of the event axis is less than the preset flatness, and determine the migration velocity for generating the first common imaging point gather as the migration velocity of the first formation. The terminal can generate a seismic image with better imaging effect and higher reliability according to the migration velocity.

[0066] When the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, it indicates that none of the above first migration velocities can be used as the migration velocity of the first formation. The terminal interpolates the multiple first migration velocities respectively to obtain multiple second migration velocities. The terminal can determine whether there is a second migration velocity that can be used as the migration velocity of the first formation among the multiple second migration velocities.

[0067] 203. For any second offset velocity, the terminal generates a second common imaging point gather based on the first target common imaging point gather, where the first target common imaging point gather is a first common imaging point gather generated by using the target first offset velocity, the target first offset velocity is a first offset velocity having the smallest difference with the second offset velocity among multiple first offset velocities, and the second common imaging point gather is used to reflect the result of pre-stack depth migration of seismic data of the imaging point by using the second offset velocity.

[0068] In an embodiment of the present application, in the process of generating a common imaging point gather of any second offset velocity, the terminal determines the difference between the second offset velocity and each of the above-mentioned first offset velocities, and determines the first offset velocity with the smallest difference as the target first offset velocity. In step 201, the terminal performs prestack depth migration on the seismic data of the imaging point according to the target first offset velocity, and obtains the first target common imaging point gather. The terminal generates a second common imaging point gather according to the amplitude values ​​of the seismic data represented by the first target common imaging point gather at different depths underground. The terminal generates a second common imaging point gather for each second offset velocity in the above manner. The terminal determines whether the second offset velocity can be used as the offset velocity of the first formation according to the straightness of the event axis of the second common imaging point gather. In the above manner, the terminal can obtain a second common imaging point gather that can reflect the result after prestack depth migration without performing prestack depth migration on the seismic data of the imaging point according to the second offset velocity, which significantly improves the efficiency of generating the second common imaging point gather.

[0069] 204. The terminal determines a target second offset velocity from the plurality of second offset velocities, determines the target second offset velocity as the offset velocity of the first formation, and the straightness of the event axis of the second common imaging point gather generated by the target second offset velocity is less than a preset straightness.

[0070] In the embodiment of the present application, in the case of a second common imaging point gather whose event straightness is less than a preset straightness, the terminal determines the target second offset velocity for generating the second common imaging point gather as the offset velocity of the first stratum. Furthermore, the terminal can perform offset imaging processing on the seismic data reflected by the first stratum according to the offset velocity of the first stratum, and obtain a seismic image that can reflect the stratum structure. Among them, the event shape of the seismic image is relatively straight, the clarity is high, and the imaging effect is good, which is convenient for technicians to further analyze and detect the underground strata according to the seismic image.

[0071] It should be noted that the above embodiment is described by taking a common imaging point in the first stratum as an example. In some embodiments, the first stratum includes multiple common imaging points. When there are multiple common imaging points in the first stratum, the terminal can perform the above processing on at least one imaging point through the above steps 201-204, and use the finally determined offset velocity as the offset velocity of the imaging point. The terminal can also interpolate the offset velocity of the imaging point to obtain the offset velocities of the remaining imaging points. The terminal uses the offset velocity field composed of the offset velocity of each imaging point in the first stratum as the offset velocity field of the first stratum.

[0072] The embodiment of the present application provides a method for determining a migration velocity. In the process of determining the migration velocity of a first formation, firstly, the seismic data of the imaging points in the first formation are pre-stacked depth migrated according to a plurality of first migration velocities to obtain a plurality of first common imaging point gathers. Since the straighter the event axis of the common imaging point gather, the better the imaging effect of the common imaging point gather and the higher the reliability. Therefore, the migration velocity corresponding to the first common imaging point gather whose event axis straightness is less than the preset straightness can be determined as the migration velocity of the first formation. In the case where the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, it indicates that the reliability of the above-mentioned plurality of migration velocities is low and none of them can be used as the migration velocity of the first formation. Then, the plurality of first migration velocities are interpolated to obtain a plurality of second migration velocities. For each second migration velocity, a second common imaging point gather is generated according to the first common imaging point gather corresponding to the first migration velocity with the smallest difference therewith. Then, the migration velocity corresponding to the second common imaging point gather whose event axis is relatively straight is used as the migration velocity of the first layer. By adopting the above method, it is no longer necessary to perform prestack depth migration on seismic data according to each second migration velocity, which significantly reduces the amount of calculation for generating the second common imaging point gathers and improves the efficiency of determining the migration velocity.

[0073] Above Figure 2 The main process of the method for determining the offset speed provided in the embodiment of the present application is exemplified, and the method for determining the offset speed is described in detail below. Figure 3 is a flowchart of another method for determining an offset speed provided in an embodiment of the present application, the method being executed by a terminal, see Figure 3 , the method comprising:

[0074] 301. The terminal obtains an initial velocity model, where the initial velocity model is used to represent the relationship between the depth of a formation and an initial offset velocity of the formation.

[0075] In an embodiment of the present application, there are multiple strata to be detected underground, and the depths of the multiple strata increase layer by layer. In the process of detecting the strata, the terminal usually performs offset imaging on the seismic data reflected by each stratum to obtain a seismic image that can reflect the stratum structure. Due to the different depths of different strata, the reflection angles of different strata to the seismic data emitted by the same shot point are also different. Therefore, in the process of offset imaging, the offset velocity of each stratum is also different. The terminal usually determines the initial offset velocity of the stratum according to the depth of the stratum through the initial velocity model. The initial offset velocity of the stratum is used to perform pre-stack depth migration on the seismic data reflected by the imaging point in the stratum, and then sort the offset seismic data according to the shot offset to obtain a common imaging point gather. Among them, pre-stack depth migration is a depth domain offset imaging technology. The common imaging point gather can reflect the results after pre-stack depth migration of seismic data collected from different detection points.

[0076] In some embodiments, the terminal can directly perform prestack depth migration on the seismic data reflected by the imaging point in the formation according to the initial migration velocity of the formation to obtain the common imaging point gather of the formation. The technician can determine whether the initial migration velocity of the formation is accurate according to the imaging quality of the common imaging point gather or the straightness of the event axis of the common imaging point gather.

[0077] In some embodiments, the terminal can construct an initial velocity model based on the seismic data of the imaging point. The seismic data of the imaging point refers to the seismic data reflected by the imaging point collected by the terminal through the detection point after the seismic wave is successfully excited from the shot point to any direction underground. The terminal performs time domain velocity analysis on the seismic data of the imaging point to obtain a time domain velocity field. Among them, the time domain velocity field is used to represent the relationship between the transmission time of the seismic data in each stratum and the offset velocity of each stratum, that is, the time domain velocity field expresses the offset velocity of the underground stratum based on time. The terminal performs pre-stack time migration on the seismic data of the imaging point to obtain a time domain migration profile. Among them, pre-stack time migration is a time domain migration imaging technology. The terminal can divide multiple underground strata and determine the depth of each stratum by interpreting the stratigraphic position of the time domain migration profile. Based on the time domain velocity field and the time domain migration profile, the terminal determines the relationship between the depth of the stratum and the offset velocity of the stratum, and constructs an initial velocity model based on this. Among them, the initial velocity model is a velocity field in the depth domain, and the depth domain velocity field expresses the offset velocity of the underground stratum based on the depth of the stratum. Optionally, the terminal may also create a depth domain velocity field based on the collected well data, which is not limited in the embodiment of the present application.

[0078] In some embodiments, after the terminal collects the seismic data of the reflection point, the collected seismic data is processed according to the conventional process of processing seismic data to obtain a time domain shot gather seismic record. Among them, conventional processing includes basic processing such as static correction, pre-stack denoising, amplitude compensation, deconvolution and velocity analysis. The time domain shot gather seismic record can represent the seismic data collected by each seismic channel over time. The terminal performs time domain velocity analysis and pre-stack time migration on the time domain shot gather record to obtain a time domain velocity field and a time domain migration profile.

[0079] 302. The terminal determines an initial migration velocity of a first formation based on an initial velocity model.

[0080] In an embodiment of the present application, the first stratum is any stratum to be detected underground. The terminal determines the depth of the first stratum and determines the initial offset velocity of the first stratum according to the initial velocity model. Optionally, the terminal can directly perform prestack depth offset on the seismic data reflected by the imaging point in the first stratum according to the initial offset velocity to obtain a common imaging point gather of the first stratum. However, when the initial velocity model is not accurate and the initial offset velocity is low in accuracy, the imaging quality of the obtained common imaging point gather is poor, it is difficult to identify effective event axes, and the reliability is low.

[0081] 303. The terminal generates a plurality of first migration velocities within a preset velocity range based on the initial migration velocity and a generation step length, wherein the generation step length is used to represent a difference between two adjacent first migration velocities, and the first migration velocities are used to perform prestack depth migration on seismic data of imaging points.

[0082] In an embodiment of the present application, in order to obtain a more accurate offset speed, the terminal enumerates the initial offset speed according to the generation step length to generate multiple first offset speeds within a preset speed range. Then, the terminal can determine whether there is an offset speed with higher accuracy among the multiple first offset speeds. The preset speed range can be a preset percentage range or a preset numerical range. Accordingly, the generation step length can be a preset percentage or a preset numerical value, which is not limited in the embodiment of the present application.

[0083] For example, when the initial offset speed is 2000m / s (meters / second), the preset speed range is 80%-120%, and the generation step size is 2%, the terminal can determine a total of 21 first offset speeds of 1600m / s, 1640m / s, 1680m / s...2360m / s and 2400m / s.

[0084] 304. For the imaging points in the first stratum, the terminal performs pre-stack depth migration on the seismic data of the imaging points according to the multiple first migration velocities, and obtains multiple first common imaging point gathers. The multiple common imaging point gathers correspond one-to-one to the multiple first migration velocities. The first common imaging point gathers are used to represent the amplitude values ​​of the seismic data at different depths underground.

[0085] In the embodiment of the present application, the imaging point is a point in the first stratum that can reflect seismic data. The first stratum includes at least one imaging point. The embodiment of the present application is described by taking an imaging point in the first stratum as an example. After the seismic wave is successfully excited from the blast point on the surface to any direction underground, the seismic wave propagates in multiple strata to be detected underground. During the propagation process, the seismic wave can be reflected to the surface by the imaging point in the stratum. Correspondingly, the terminal can collect the seismic wave reflected by the imaging point through multiple detectors on the surface, that is, collect the seismic data reflected by the imaging point. Among them, the seismic data collected by one detector is called a seismic trace. The seismic trace records multiple seismic data collected by the corresponding detector. Then, the terminal performs pre-stack depth migration on the collected seismic data according to multiple first migration velocities, and obtains multiple first common imaging point gathers. The terminal can determine the amplitude values ​​of the above seismic data at different depths underground through the first common imaging point gathers.

[0086] In some embodiments, the terminal can perform pre-stack depth migration on the time-domain shot gather seismic records obtained through conventional processing according to the first migration velocity to obtain a first common imaging point gather corresponding to the first migration velocity.

[0087] 305. When the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, the terminal determines a second target common imaging point gather, and the second target common imaging point gather is the first common imaging point gather with the smallest difference between the straightness of the event axis and the preset straightness.

[0088] In the embodiment of the present application, the event axis of the first common imaging point gather refers to the line connecting the extreme values ​​(commonly known as peaks or troughs) of the same vibration phase of the seismic data in each seismic channel. Therefore, in the first common imaging point gather, the terminal determines the maximum amplitude value or the minimum amplitude value of the seismic data recorded in each seismic channel. Then the terminal connects the maximum amplitude values ​​recorded in each seismic channel, or connects the minimum amplitude values ​​recorded in each seismic channel, to obtain the event axis of the first common imaging point gather and the straightness of the event axis. The terminal can determine the imaging effect of the first common imaging point gather through the straightness of the event axis. The straighter the event axis, the better the imaging effect of the common imaging point gather and the higher the reliability. When the straightness of the event axis is not less than the preset straightness, it indicates that the event axis is relatively curved; when the straightness of the event axis is less than the preset straightness, it indicates that the event axis is relatively straight. Among them, the preset straightness can be a preset angle, such as 10°, 15° or 20°, which is not limited in the embodiment of the present application. Therefore, the terminal can determine the first common imaging point gather whose straightness of the event axis is less than the preset straightness, and determine the first migration velocity for generating the first common imaging point gather as the migration velocity of the first formation. The terminal can generate a seismic image with better imaging effect and higher reliability according to the migration velocity.

[0089] In some embodiments, the terminal stacks the data of each seismic trace in the first common imaging point gather to obtain a stacked section. The terminal determines the offset velocity of the first formation according to at least one of the straightness of the event axis of the first common imaging point gather and the imaging effect of the stacked section. For example, the terminal determines a first common imaging point gather from multiple first common imaging point gathers, in which the event axis is relatively straight, the event axis continuity of the stacked section is good, the signal-to-noise ratio is high, and the fault is relatively clear, and determines the first offset velocity generated by the first common imaging point gather as the offset velocity of the first formation.

[0090] When the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, it indicates that the event axis of all the first common imaging point gathers at the depth of the first formation has not been flattened, and the above-mentioned multiple first offset velocities cannot be used as the offset velocity of the first formation. Therefore, the terminal regenerates a new batch of offset velocities and common imaging point gathers corresponding to the new offset velocities, and determines whether there is a new offset velocity that can be used as the offset velocity of the first formation according to the straightness of the event axis of the newly generated common imaging point gathers.

[0091] In the process of generating a new offset velocity, the terminal can generate a new offset velocity based on the first common imaging point gather with a relatively straight event. The terminal determines the difference between the straightness of the event of each first common imaging point gather and the preset straightness, and generates a new offset velocity based on the first common imaging point gather with the smallest difference. The following steps illustrate the specific process of the terminal generating a new offset velocity based on the second target common imaging point gather (the first common imaging point gather with a relatively straight event).

[0092] 306. The terminal determines a third migration velocity based on the second target common imaging point gather, where the third migration velocity is the first migration velocity for generating the second target common imaging point gather.

[0093] In the embodiment of the present application, after the terminal determines the second target common imaging point gather with a relatively straight event axis, the terminal determines the first offset velocity for generating the second target common imaging point gather, which is referred to as the third offset velocity for ease of description. Since the event axis of the second target common imaging point gather is relatively straight, the difference between the third offset velocity and the offset velocity with higher accuracy is small, so the terminal can generate multiple new offset velocities based on the third offset velocity.

[0094] 307. The terminal interpolates the third offset speed within a preset speed range according to an interpolation interval to obtain a plurality of second offset speeds.

[0095] In an embodiment of the present application, in order to obtain a more accurate offset speed, the terminal interpolates the third offset speed according to the interpolation interval within a preset speed range to obtain multiple second offset speeds. Then, the terminal can determine whether there is an offset speed with higher accuracy among the multiple second offset speeds. The preset speed range can be a preset percentage range or a preset numerical range. Accordingly, the interpolation interval can be a preset percentage or a preset numerical value, which is not limited in the embodiment of the present application.

[0096] In some embodiments, the terminal may also generate the second offset velocity in other ways. For example, after the terminal generates multiple first offset velocities according to the initial offset velocity, the terminal can use some of the first offset velocities as the second offset velocity. Then, the terminal performs prestack depth migration on the seismic data of the imaging point only according to the first offset velocity to obtain the first common imaging point gather. When the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, the terminal generates the second common imaging point gather corresponding to the second offset velocity. For example, when the initial offset velocity is 2000m / s, the preset velocity range is 80%-120%, and the generation step size is 1%, the terminal can determine 41 offset velocities of 1600m / s, 1620m / s, 1640m / s...2380m / s and 2400m / s, corresponding to 80%, 81%, 82%...119% and 120% respectively. The terminal uses the offset speeds corresponding to 80%, 82%, 84% ... 118% and 120% as the first offset speeds, and uses the offset speeds corresponding to 81%, 83%, 85% ... 117% and 119% as the second offset speeds.

[0097] 308. For any second offset velocity, the terminal generates a second common imaging point gather based on the first target common imaging point gather, where the first target common imaging point gather is a first common imaging point gather generated by the target first offset velocity, the target first offset velocity is the first offset velocity having the smallest difference with the second offset velocity among multiple first offset velocities, and the second common imaging point gather is used to reflect the result of pre-stack depth migration of seismic data of the imaging point by the second offset velocity.

[0098] In an embodiment of the present application, in the process of generating a common imaging point gather of any second offset velocity, the terminal determines the difference between the second offset velocity and each of the above-mentioned first offset velocities, and determines the first offset velocity with the smallest difference as the target first offset velocity. Among them, if there are two first offset velocities with the smallest difference, the terminal selects one of them as the target first offset velocity. Since the terminal performs prestack depth migration on the seismic data of the imaging point according to the target first offset velocity in the above step 304, the first target common imaging point gather is obtained. The terminal generates a second common imaging point gather according to the amplitude values ​​of the seismic data represented by the first target common imaging point gather at different depths underground. The terminal can generate a second common imaging point gather for each second offset velocity in the above manner. The terminal determines whether the second offset velocity can be used as the offset velocity of the first formation according to the straightness of the event axis of the second common imaging point gather. In the above manner, the terminal can obtain a second common imaging point gather that can reflect the result after prestack depth migration without performing prestack depth migration on the seismic data of the imaging point according to the second offset velocity, which can improve the efficiency of generating the second common imaging point gather.

[0099] In some embodiments, the terminal generates a second common imaging point gather according to the amplitude value of the seismic data represented by the first target common imaging point gather. The second common imaging point gather is used to represent the amplitude value of the seismic data at the first depth, and the first depth is the depth of the imaging point. Therefore, the terminal can generate the second common imaging point gather by determining the amplitude value of the seismic data at the first depth. In the process of determining the amplitude value of the seismic data at the first depth, the technician first emits a first ray to the surface at the depth of the imaging point. After the first ray successfully emits the surface, the terminal can determine the travel time and target position of the first ray. The first ray is a ray emitted to the surface at the depth of the imaging point according to a preset emission angle. The preset emission angle can be an angle in the range of 0° to 90°, which is not limited in the embodiment of the present application. The travel time is the time taken for the first ray to be emitted from the emission to the emission of the surface. The target position is the position where the first ray emits the surface. After that, the technician can emit the second ray underground at the depth of the target position. In response to the successful emission of the second ray, the terminal counts down based on the travel time, and determines the depth reached by the second ray when the travel time is exhausted as the second depth. The terminal determines the amplitude value of the seismic data at the second depth based on the first target common imaging point gather, and uses the amplitude value of the seismic data at the second depth as the amplitude value of the seismic data at the first depth.

[0100] In some embodiments, the terminal can determine the travel time and target position of the first ray according to the transmission speed of the first ray and the preset exit angle. The terminal obtains the initial offset velocity of each stratum according to the initial velocity model. The transmission speed of the first ray in each stratum is the initial offset velocity of each stratum. Based on the preset exit angle and the transmission speed of the first ray in each stratum, the terminal determines the incident angle and the exit angle of the first ray at each stratum interface by the law of refraction. The terminal determines the travel time and target position of the first ray based on the transmission speed of the first ray in each stratum, the incident angle and the exit angle of the first ray at each stratum interface, and the first depth.

[0101] Optionally, the terminal can obtain the velocity curve {z′ corresponding to the first target common imaging point gather according to the depth of the stratum represented by the initial velocity model and the initial migration velocity of the stratum. i ,v′ i} i＝1,n and the velocity curve {z i ,v i} i＝1,n The velocity curve can represent the relationship between the depth of the underground depth sampling point and the migration velocity. n is the maximum number of depth sampling points. i ,v i are the depth and initial migration velocity of the i-th depth sampling point in the velocity curve corresponding to the second common imaging point gather to be generated, respectively, i ′,v i ′ are the depth and initial migration velocity of the i-th depth sampling point in the velocity curve corresponding to the first target common imaging point gather.

[0102] For example, the first depth of the imaging point of the first formation is z i ; The depth of the previous layer of the first layer is z i-1 ; The depth of the ground surface is z0; The preset emission angle is α i,j , j is the exit angle index, used to identify different preset exit angles. The first ray starts from the first depth z i After being emitted, when the ray reaches the depth z i-1 When , the terminal can determine the lateral offset of the first ray by the following formula (1).

[0103] dx i,j =(z i -z i-1 )·tan(α i,j ) (1)

[0104] Among them, dx i,j For the first ray from the first depth z i Reach depth z i-1The lateral offset during the process. α i,j is the preset emission angle.

[0105] Then, the terminal can determine the angle of the first ray emitted from the first interface by the following formula (2), which is also the formula of the refraction law. The first interface is the interface between the first stratum and the layer above the first stratum.

[0106] sinα i,j / v1=sin α i-1,j / v2 (2)

[0107] Among them, α i, is the preset exit angle, that is, the angle between the first ray in the first stratum and the normal of the first interface, which can also be called the incident angle of the first ray at the first interface. i-1, is the angle between the first ray in the previous stratum and the normal of the first interface, which can also be called the exit angle of the first ray at the first interface. v1 is the transmission speed of the first ray in the first stratum. v2 is the transmission speed of the first ray in the previous stratum. Furthermore, the terminal can determine the incident angle and exit angle of the first ray at each stratum interface in sequence through the following formula (3) until the first ray is emitted from the surface.

[0108]

[0109] Where k is the index of the ray unit at different depths of the first ray. k,j is the first ray at depth z k The stratum and depth are z k-1 The incident angle at the interface of the strata, α k-1, is the angle of departure of the first ray at the interface. k is the first ray at depth z k The transmission velocity in the formation. k-1 is the first ray at depth z k-1 The transmission speed in the formation.

[0110] Then, the terminal can recursively calculate the travel time of the first ray through the following formula (4), and recursively calculate the position where the first ray exits the ground through the following formula (5).

[0111]

[0112]

[0113] Among them, T i,j For the first ray from the first depth z i The time it takes from launch to exiting the Earth's surface. i,jis the position where the first ray exits the surface, that is, the first ray from the first depth z i The sum of the lateral displacements on the way to the surface. k,j and v k Compared with α in the above formula (3) k,j and v k The meaning of is the same, so I will not repeat it here. When k = 1, z k-1 is 0, that is, the surface depth z0 is 0.

[0114] In some embodiments, the terminal determines the depth reached by the second ray when the travel time is exhausted as the second depth. However, the first target common imaging point gather may or may not have a depth sampling point at the second depth position. In the case where the first target common imaging point gather has a depth sampling point at the second depth, the terminal uses the amplitude value of the depth sampling point as the amplitude value of the seismic data at the second depth. In the case where the first target common imaging point gather has or does not have a depth sampling point at the second depth, the terminal interpolates the amplitude value of at least one depth sampling point adjacent to the second depth to obtain the amplitude value of the seismic data at the second depth.

[0115] The terminal can perform the above processing on each second migration velocity in the above manner to generate multiple second common imaging point gathers. The terminal does not need to perform prestack depth migration on the seismic data of the imaging point according to the second migration velocity to obtain the second common imaging point gather that can reflect the result after prestack depth migration, which can improve the efficiency of generating the second common imaging point gather.

[0116] 309. The terminal determines a target second offset velocity from the multiple second offset velocities, determines the target second offset velocity as the offset velocity of the first formation, and the straightness of the event axis of the second common imaging point gather generated by the target second offset velocity is less than a preset straightness.

[0117] In an embodiment of the present application, in the case where there is a second common imaging point gather whose event straightness is less than a preset straightness, the terminal determines the target second offset velocity for generating the second common imaging point gather as the offset velocity of the first stratum. Furthermore, the terminal can perform prestack depth migration on the seismic data reflected by the first stratum according to the offset velocity of the first stratum to obtain a seismic image that can reflect the stratum structure. Among them, the event shape of the seismic image is relatively straight, the clarity is high, and the imaging effect is good, which is convenient for technicians to further analyze and detect the underground strata according to the seismic image. In addition, if there is still no second common imaging point gather with a relatively straight event, the terminal repeats the above steps 302-308 to regenerate multiple new offset velocities and common imaging point gathers until there is a common imaging point gather with a relatively straight event.

[0118] It should be noted that the above embodiment is described by taking a common imaging point in the first stratum as an example. In some embodiments, the first stratum includes multiple common imaging points. When there are multiple common imaging points in the first stratum, the terminal can perform the above processing on at least one imaging point through the above steps 301-309, and use the finally determined offset velocity as the offset velocity of the imaging point. The terminal can also interpolate the offset velocity of the imaging point to obtain the offset velocities of the remaining imaging points. The terminal uses the offset velocity field composed of the offset velocity of each imaging point in the first stratum as the offset velocity field of the first stratum.

[0119] 310. In response to obtaining the offset velocity of the first stratum, the terminal determines the offset velocity of the second stratum based on a plurality of common imaging point gathers of imaging points in the second stratum, where the second stratum is a layer below the first stratum.

[0120] In the embodiment of the present application, the terminal determines the offset velocity of each stratum layer by layer from top to bottom. In response to the terminal obtaining the offset velocity of the first stratum, the terminal processes the seismic data of the imaging point in the second stratum by executing the above steps 301-309 to obtain a plurality of common imaging point gathers, and determines the offset velocity of the second stratum according to the straightness of the event axis of each common imaging point gather. The process of generating the common imaging point gather and the process of determining the offset velocity are the same as the above steps, and will not be repeated here.

[0121] In order to more clearly explain the process of determining the displacement velocity of the formation by the terminal, Figure 4 The flowchart shown in FIG. 1 illustrates the process of determining the displacement velocity of any formation by the terminal. Figure 4 As shown, the terminal first generates N offset velocities according to the initial offset velocity of the formation. Then, the terminal performs prestack depth offset on the seismic data of the formation only according to the N / 2 offset velocities, and obtains N / 2 first common imaging point gathers. In the case that the event axis of each first common imaging point gather is not straight, the terminal generates a second common imaging point gather corresponding to the remaining offset velocities according to the first common imaging point gather. Then, the terminal determines the second common imaging point gather with a relatively straight event axis, and uses the offset velocity of the second common imaging point gather as the offset velocity of the formation. Then, the terminal performs prestack depth offset on the seismic data of the formation according to the offset velocity of the formation to obtain a common imaging point gather. The terminal verifies whether the offset velocity is accurate according to the straightness of the event axis of the common imaging point gather. When the event axis is relatively straight, it indicates that the accuracy of the offset velocity is high. The terminal determines the offset velocity as the offset velocity of the above-mentioned formation, and continues to determine the offset velocity of the next formation.

[0122] Compared with pre-stack depth migration directly based on the initial migration velocity of the formation, the above method can determine a more accurate migration velocity and obtain a seismic image with better imaging effect. Figure 5 A schematic diagram of imaging shallow, low signal-to-noise ratio seismic data. Figure 5 The left side is a stacked section obtained by performing pre-stack depth migration on the above seismic data according to the initial migration velocity of the formation and then stacking it. Figure 5 The right side is a stacked section obtained by determining the displacement velocity of the formation according to the above method, performing pre-stack depth migration on the above seismic data according to the migration velocity, and then stacking. It can be seen that the continuity of the event axis of the stacked section on the right side is good, and the fault is clearer. Therefore, the displacement velocity determination method provided in the embodiment of the present application can more accurately determine the displacement velocity of the formation, which is an effective method for accurately imaging seismic data with a low signal-to-noise ratio.

[0123] In addition, in order to compare the method of generating the second common imaging point gathers proposed in the embodiment of the present application (the method of generating new common imaging point gathers based on the existing common imaging point gathers, hereinafter referred to as the method provided by the present application) with the traditional method of generating common imaging point gathers by using deep prestack migration, the following method is used. Figure 6 The 7-layer horizontal layered model shown in the figure is used to compare the above two methods. Figure 6 In the horizontal layered model shown, the initial migration speed of each layer from top to bottom is 2000m / s, 2500m / s, 3000m / s, 3500m / s, 4000m / s, 4500m / s and 5000m / s respectively. Taking the first layer as an example, the terminal generates 41 first migration speeds based on the initial migration speed of the first layer, according to the preset speed range of 80% to 120% and the generation step of 1%. If the traditional method is adopted, it is necessary to perform prestack depth migration on the seismic data according to each first migration speed, calculate 41 prestack depth migrations, and obtain 41 common imaging point gathers, which is a large amount of calculation. If the method provided by the present application is adopted, the prestack depth migration can be performed in a rarefied range, that is, in the preset speed range of 80% to 120%, the prestack depth migration is performed according to the step of 2%, and only 21 prestack depth migrations are required to obtain 21 common imaging point gathers. Then the remaining 20 common imaging point gathers are generated by the method provided by the present application. The following takes 91% of the migration speed as an example to demonstrate the imaging effects of the above two methods. Figure 7As shown, on the left is the common imaging point gather obtained by the terminal according to the prestack depth migration of the seismic data at an offset velocity of 91%. On the right is the common imaging point gather generated by the terminal according to the offset velocity of 92%, and the common imaging point gather generated by the method provided by the present application corresponds to an offset velocity of 91%. By comparison, it can be seen that there is almost no difference between the two. That is, the imaging effect of the seismic image obtained by the method provided by the present application is guaranteed.

[0124] In addition, according to Figure 8 The actual underground model shown in the figure verifies the above two methods. Figure 8 As shown, the strata in the selected actual underground model are mainly flat layers, and the medium-deep layer (about 3000m-4000m) has a reverse fault structure. The following takes the processing of seismic data in the medium-deep layer as an example. Based on the initial offset velocity of the medium-deep layer, the terminal generates 11 first offset velocities according to the preset velocity range of 90% to 110% and the generation step of 2%. If the above-mentioned traditional generation method is adopted, it is necessary to perform pre-stack depth migration on the seismic data according to each first offset velocity, calculate 11 pre-stack depth migrations, and obtain 11 common imaging point gathers. Taking the example of the terminal performing pre-stack depth migration through the pre-stack depth migration module with 5 computing nodes in GeoEast (an application for seismic data processing), it takes 4.5 minutes for the terminal to generate a common imaging point gather, and it takes about 11*4.5=49.5 minutes to complete the generation. If the method provided by this application is adopted, the terminal only needs to perform prestack depth migration for the five migration velocities of 92%, 96%, 100%, 104%, and 108%, and the common imaging point gathers of the other migration velocities (90%, 94%, 98%, 102%, 106%, and 110%) are obtained by the method provided by this application. Since it only takes 21 seconds to generate a common imaging point gather using the method provided by this application, the total time required for the above calculation is: 4.5 minutes * 5 + 21 seconds * 6 = 24.5 minutes, which significantly improves the calculation efficiency compared to the previous 49.5 minutes.

[0125] The following takes 90% of the migration speed as an example to demonstrate the imaging effects of the above two methods. Fig. 9 As shown, on the left is the common imaging point gather obtained by the terminal according to the prestack depth migration of the seismic data at a migration velocity of 90%. On the right is the common imaging point gather generated by the terminal according to the migration velocity of 92%, which is the common imaging point gather generated by the method provided by the present application, and corresponds to the migration velocity of 90%. As can be seen from the figure, the straightness of the coinciding axes of the two is consistent. Therefore, for some migration velocities, the common imaging point gather generated by the method provided by the present application can be used instead of the common imaging point gather obtained by prestack depth migration according to the migration velocity, which can improve the calculation efficiency.

[0126] In addition, due to Figure 8 The lateral velocity of the actual underground model shown does not change much, so the terminal can only perform a prestack depth migration for the 100% migration velocity to generate a common imaging point gather. The common imaging point gathers corresponding to the other ten migration velocities are all generated by the method provided in this application. The following also takes the 90% migration velocity as an example to demonstrate the imaging effects of the above two methods. Fig.10 As shown, on the left is the common imaging point gather obtained by the terminal according to the 90% migration velocity by prestack depth migration of seismic data. On the right is the common imaging point gather generated by the terminal according to the 100% migration velocity using the method provided by the present application, and the common imaging point gather corresponds to the 90% migration velocity. Fig.10 It can be seen that the straightness of the event axes of the two is still consistent. Moreover, using the method provided by the present application, the total time required is 4.5 minutes + 21 seconds * 10 = 8 minutes, while using the above-mentioned traditional generation method requires 49.5 minutes. Therefore, the offset velocity determination method provided by the present application can not only accurately determine the offset velocity of the underground strata, but also significantly save calculation time and greatly improve the calculation efficiency. Furthermore, the terminal can perform offset imaging processing on the seismic data reflected by each stratum according to the offset velocity of each stratum underground, and obtain a seismic image that can reflect the stratum structure. Among them, the shape of the event axis of the seismic image is relatively straight, the clarity is high, and the imaging effect is good, so that technicians can further analyze and detect the underground strata based on the seismic image.

[0127] The embodiment of the present application provides a method for determining a migration velocity. In the process of determining the migration velocity of a first formation, firstly, the seismic data of the imaging points in the first formation are pre-stacked depth migrated according to a plurality of first migration velocities to obtain a plurality of first common imaging point gathers. Since the straighter the event axis of the common imaging point gather, the better the imaging effect of the common imaging point gather and the higher the reliability. Therefore, the migration velocity corresponding to the first common imaging point gather whose event axis straightness is less than the preset straightness can be determined as the migration velocity of the first formation. In the case where the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, it indicates that the reliability of the above-mentioned plurality of migration velocities is low and none of them can be used as the migration velocity of the first formation. Then, the plurality of first migration velocities are interpolated to obtain a plurality of second migration velocities. For each second migration velocity, a second common imaging point gather is generated according to the first common imaging point gather corresponding to the first migration velocity with the smallest difference therewith. Then, the migration velocity corresponding to the second common imaging point gather whose event axis is relatively straight is used as the migration velocity of the first layer. By adopting the above method, it is no longer necessary to perform prestack depth migration on seismic data according to each second migration velocity, which significantly reduces the amount of calculation for generating the second common imaging point gathers and improves the efficiency of determining the migration velocity.

[0128] Fig.11 is a schematic diagram of the structure of a device for determining an offset velocity provided in an embodiment of the present application. Fig.11 The device includes: an offset module 1101, an interpolation module 1102, a first generation module 1103 and a first determination module 1104.

[0129] The migration module 1101 is used to perform prestack depth migration on the seismic data of the imaging points in the first stratum to obtain a plurality of first common imaging point gathers, where the first common imaging point gathers are used to represent the amplitude values ​​of the seismic data at different depths underground;

[0130] An interpolation module 1102 is used to interpolate a plurality of first migration velocities respectively to obtain a plurality of second migration velocities when the straightness of the event axis of each first common imaging point gather is less than a preset straightness, wherein the first migration velocities are used to perform prestack depth migration on the seismic data of the imaging point;

[0131] The first generating module 1103 is used to generate a second common imaging point gather for any second migration velocity based on the first target common imaging point gather, where the first target common imaging point gather is a first common imaging point gather generated by using the target first migration velocity, the target first migration velocity is the first migration velocity having the smallest difference with the second migration velocity among the plurality of first migration velocities, and the second common imaging point gather is used to reflect the result of prestack depth migration of the seismic data of the imaging point by using the second migration velocity;

[0132] The first determination module 1104 is used to determine a target second offset velocity from a plurality of second offset velocities, determine the target second offset velocity as the offset velocity of the first formation, and ensure that the straightness of the event axis of the second common imaging point gather generated by the target second offset velocity is not less than a preset straightness.

[0133] In some embodiments, the second common imaging point gather is used to represent the amplitude value of the seismic data at a first depth, where the first depth is the depth of the location of the imaging point; Fig.12 is a schematic diagram of the structure of another offset speed determination device provided in an embodiment of the present application, see Fig.12 , the first generation module 1103 includes:

[0134] The acquisition unit 11031 is used to acquire the travel time and target position of the first ray, where the first ray is a ray emitted toward the surface at a preset emission angle at the location of the imaging point, the travel time is the time taken for the first ray to be emitted from the surface, and the target position is the position where the first ray is emitted from the surface;

[0135] A first determining unit 11032 is configured to, in response to the second ray being successfully emitted, count down based on the travel time, and determine the depth reached by the second ray when the travel time is exhausted as a second depth, wherein the second ray is a ray emitted underground at a target position;

[0136] A second determining unit 11033 is used to determine the amplitude value of the seismic data at a second depth based on the first target common imaging point gather;

[0137] The third determining unit 11034 is configured to use the amplitude value of the seismic data at the second depth as the amplitude value of the seismic data at the first depth.

[0138] In some embodiments, the acquisition unit 11031 is used to obtain the initial offset velocity of each formation; based on the preset exit angle and the transmission velocity of the first ray in each formation, the incident angle and the exit angle of the first ray at each formation interface are determined by the law of refraction, and the transmission velocity of the first ray in each formation is the initial offset velocity of each formation; based on the transmission velocity of the first ray in each formation, the incident angle and the exit angle of the first ray at each formation interface and the first depth, the travel time and target position of the first ray are determined.

[0139] In some embodiments, the second determination unit 11033 is used to, when there is a depth sampling point at the second depth in the first target common imaging point gather, use the amplitude value of the depth sampling point as the amplitude value of the seismic data at the second depth; and when there is or is not a depth sampling point at the second depth in the first target common imaging point gather, interpolate the amplitude value of at least one adjacent depth sampling point at the second depth to obtain the amplitude value of the seismic data at the second depth.

[0140] In some embodiments, the apparatus further comprises:

[0141] An acquisition module 1105 is used to acquire an initial velocity model, where the initial velocity model is used to represent the relationship between the depth of a formation and an initial migration velocity of the formation;

[0142] A second determination module 1106 is used to determine an initial migration velocity of the first formation based on the initial velocity model;

[0143] The second generating module 1107 is used to generate a plurality of first offset velocities within a preset speed range based on the initial offset velocity and according to a generating step length, wherein the generating step length is used to represent a difference between two adjacent first offset velocities.

[0144] In some embodiments, the apparatus further comprises:

[0145] An analysis module 1108 is used to perform time domain velocity analysis on the seismic data of the imaging point to obtain a time domain velocity field, where the time domain velocity field is used to represent the relationship between the transmission time of the seismic data in each stratum and the offset velocity of each stratum;

[0146] The migration module 1101 is also used to perform pre-stack time migration on the seismic data of the imaging point to obtain a time domain migration profile, and the time domain migration profile is used to divide multiple underground strata and determine the depth of each stratum;

[0147] The construction module 1109 is used to construct an initial velocity model based on the time domain velocity field and the time domain migration profile.

[0148] In some embodiments, the interpolation module 1102 is used to determine a second target common imaging point gather when the straightness of the event axis of each first common imaging point gather is less than a preset straightness, the second target common imaging point gather being the first common imaging point gather having the smallest difference between the straightness of the event axis and the preset straightness; determine a third offset velocity based on the second target common imaging point gather, the third offset velocity being the first offset velocity for generating the second target common imaging point gather; and interpolate the third offset velocity within a preset velocity range according to the interpolation interval to obtain a plurality of second offset velocities.

[0149] In some embodiments, the apparatus further comprises:

[0150] The third determination module 1110 is used to determine the migration velocity of the second formation based on a plurality of common imaging point gathers of imaging points in the second formation in response to obtaining the migration velocity of the first formation, where the second formation is a layer below the first formation.

[0151] The embodiment of the present application provides a device for determining a migration velocity. In the process of determining the migration velocity of a first formation, firstly, the seismic data of the imaging points in the first formation are respectively pre-stacked depth migrated according to a plurality of first migration velocities to obtain a plurality of first common imaging point gathers. Since the straighter the event axis of the common imaging point gather, the better the imaging effect of the common imaging point gather and the higher the reliability. Therefore, the migration velocity corresponding to the first common imaging point gather whose event axis straightness is less than the preset straightness can be determined as the migration velocity of the first formation. In the case where the straightness of the event axis of each first common imaging point gather is not less than the preset straightness, it indicates that the reliability of the above-mentioned plurality of migration velocities is low and none of them can be used as the migration velocity of the first formation. Then, the plurality of first migration velocities are interpolated respectively to obtain a plurality of second migration velocities. For each second migration velocity, a second common imaging point gather is generated according to the first common imaging point gather corresponding to the first migration velocity with the smallest difference therewith. Then, the migration velocity corresponding to the second common imaging point gather whose event axis is relatively straight is used as the migration velocity of the first layer. By adopting the above method, it is no longer necessary to perform prestack depth migration on seismic data according to each second migration velocity, which significantly reduces the amount of calculation for generating the second common imaging point gathers and improves the efficiency of determining the migration velocity.

[0152] It should be noted that: the offset speed determination device provided in the above embodiment is only illustrated by the division of the above functional modules. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the terminal is divided into different functional modules to complete all or part of the functions described above. In addition, the offset speed determination device provided in the above embodiment and the offset speed determination method embodiment belong to the same concept, and the specific implementation process thereof is detailed in the method embodiment, which will not be repeated here.

[0153] An embodiment of the present application further provides a terminal, which includes a processor and a memory, wherein at least one computer program is stored in the memory, and the at least one computer program is loaded and executed by the processor to implement the offset speed determination method of the above embodiment.

[0154] Fig.13 It is a structural diagram of a terminal provided in an embodiment of the present application.

[0155] The terminal 1300 includes a processor 1301 and a memory 1302 .

[0156] The processor 1301 may include one or more processing cores, such as a 4-core processor, an 8-core processor, etc. The processor 1301 may be implemented in at least one hardware form of DSP (Digital Signal Processing), FPGA (Field Programmable Gate Array), and PLA (Programmable Logic Array). The processor 1301 may also include a main processor and a coprocessor. The main processor is a processor for processing data in an awake state, also known as a CPU (Central Processing Unit); the coprocessor is a low-power processor for processing data in a standby state. In some embodiments, the processor 1301 may be integrated with a GPU (Graphics Processing Unit), which is responsible for rendering and drawing the content to be displayed on the display screen. In some embodiments, the processor 1301 may also include an AI (Artificial Intelligence) processor, which is used to process computing operations related to machine learning.

[0157] The memory 1302 may include one or more computer-readable storage media, which may be non-transitory. The memory 1302 may also include a high-speed random access memory and a non-volatile memory, such as one or more disk storage devices and flash memory storage devices. In some embodiments, the non-transitory computer-readable storage medium in the memory 1302 is used to store at least one computer program, which is used to be owned by the processor 1301 to implement the offset velocity determination method provided in the method embodiment of the present application.

[0158] In some embodiments, the terminal 1300 may further optionally include: a peripheral device interface 1303 and at least one peripheral device. The processor 1301, the memory 1302 and the peripheral device interface 1303 may be connected via a bus or a signal line. Each peripheral device may be connected to the peripheral device interface 1303 via a bus, a signal line or a circuit board. Optionally, the peripheral device includes: at least one of a radio frequency circuit 1304, a display screen 1305, a camera assembly 1306, an audio circuit 1307 and a power supply 1308.

[0159] The peripheral device interface 1303 may be used to connect at least one peripheral device related to I / O (Input / Output) to the processor 1301 and the memory 1302. In some embodiments, the processor 1301, the memory 1302, and the peripheral device interface 1303 are integrated on the same chip or circuit board; in some other embodiments, any one or two of the processor 1301, the memory 1302, and the peripheral device interface 1303 may be implemented on a separate chip or circuit board, which is not limited in this embodiment.

[0160] The radio frequency circuit 1304 is used to receive and transmit RF (Radio Frequency) signals, also known as electromagnetic signals. The radio frequency circuit 1304 communicates with the communication network and other communication devices through electromagnetic signals. The radio frequency circuit 1304 converts the electrical signal into an electromagnetic signal for transmission, or converts the received electromagnetic signal into an electrical signal. Optionally, the radio frequency circuit 1304 includes: an antenna system, an RF transceiver, one or more amplifiers, a tuner, an oscillator, a digital signal processor, a codec chipset, a user identity module card, and the like. The radio frequency circuit 1304 can communicate with other devices through at least one wireless communication protocol. The wireless communication protocol includes, but is not limited to: a metropolitan area network, various generations of mobile communication networks (2G, 3G, 4G and 5G), a wireless local area network and / or a WiFi (Wireless Fidelity) network. In some embodiments, the radio frequency circuit 1304 may also include circuits related to NFC (Near Field Communication), which is not limited in this application.

[0161] The display screen 1305 is used to display a UI (User Interface). The UI may include graphics, text, icons, videos, and any combination thereof. When the display screen 1305 is a touch display screen, the display screen 1305 also has the ability to collect touch signals on the surface or above the surface of the display screen 1305. The touch signal can be input to the processor 1301 as a control signal for processing. At this time, the display screen 1305 can also be used to provide virtual buttons and / or virtual keyboards, also known as soft buttons and / or soft keyboards. In some embodiments, the display screen 1305 can be one, set on the front panel of the terminal 1300; in other embodiments, the display screen 1305 can be at least two, respectively set on different surfaces of the terminal 1300 or in a folding design; in other embodiments, the display screen 1305 can be a flexible display screen, set on a curved surface or a folding surface of the terminal 1300. Even, the display screen 1305 can also be set to a non-rectangular irregular shape, that is, a special-shaped screen. The display screen 1305 can be made of materials such as LCD (Liquid Crystal Display) and OLED (Organic Light-Emitting Diode).

[0162] The camera assembly 1306 is used to capture images or videos. Optionally, the camera assembly 1306 includes a front camera and a rear camera. The front camera is arranged on the front panel of the terminal 1300, and the rear camera is arranged on the back of the terminal 1300. In some embodiments, there are at least two rear cameras, which are any one of a main camera, a depth of field camera, a wide-angle camera, and a telephoto camera, so as to realize the fusion of the main camera and the depth of field camera to realize the background blur function, the fusion of the main camera and the wide-angle camera to realize the panoramic shooting and VR (Virtual Reality) shooting function or other fusion shooting functions. In some embodiments, the camera assembly 1306 may also include a flash. The flash can be a monochrome temperature flash or a dual-color temperature flash. A dual-color temperature flash refers to a combination of a warm light flash and a cold light flash, which can be used for light compensation at different color temperatures.

[0163] The audio circuit 1307 may include a microphone and a speaker. The microphone is used to collect sound waves from the user and the environment, and convert the sound waves into electrical signals and input them into the processor 1301 for processing, or input them into the radio frequency circuit 1304 to achieve voice communication. For the purpose of stereo acquisition or noise reduction, there may be multiple microphones, which are respectively arranged at different parts of the terminal 1300. The microphone may also be an array microphone or an omnidirectional acquisition microphone. The speaker is used to convert the electrical signal from the processor 1301 or the radio frequency circuit 1304 into sound waves. The speaker may be a traditional film speaker or a piezoelectric ceramic speaker. When the speaker is a piezoelectric ceramic speaker, it can not only convert the electrical signal into sound waves audible to humans, but also convert the electrical signal into sound waves inaudible to humans for purposes such as ranging. In some embodiments, the audio circuit 1307 may also include a headphone jack.

[0164] The power supply 1308 is used to power various components in the terminal 1300. The power supply 1308 can be an alternating current, a direct current, a disposable battery, or a rechargeable battery. When the power supply 1308 includes a rechargeable battery, the rechargeable battery can support wired charging or wireless charging. The rechargeable battery can also be used to support fast charging technology.

[0165] In some embodiments, the terminal 1300 further includes one or more sensors 1309 . The one or more sensors 1309 include, but are not limited to: an acceleration sensor 1130 , a gyroscope sensor 1311 , a pressure sensor 1312 , an optical sensor 1313 , and a proximity sensor 1314 .

[0166] The acceleration sensor 1130 can detect the magnitude of acceleration on the three coordinate axes of the coordinate system established by the terminal 1300. For example, the acceleration sensor 1130 can be used to detect the components of gravity acceleration on the three coordinate axes. The processor 1301 can control the display screen 1305 to display the user interface in a horizontal view or a vertical view according to the gravity acceleration signal collected by the acceleration sensor 1130. The acceleration sensor 1130 can also be used to collect motion data of games or users.

[0167] The gyro sensor 1311 can detect the body direction and rotation angle of the terminal 1300, and the gyro sensor 1311 can cooperate with the acceleration sensor 1130 to collect the user's 3D actions on the terminal 1300. The processor 1301 can implement the following functions based on the data collected by the gyro sensor 1311: motion sensing (such as changing the UI according to the user's tilt operation), image stabilization during shooting, game control, and inertial navigation.

[0168] The pressure sensor 1312 can be set on the side frame of the terminal 1300 and / or the lower layer of the display screen 1305. When the pressure sensor 1312 is set on the side frame of the terminal 1300, it can detect the user's holding signal of the terminal 1300, and the processor 1301 performs left and right hand recognition or shortcut operation according to the holding signal collected by the pressure sensor 1312. When the pressure sensor 1312 is set on the lower layer of the display screen 1305, the processor 1301 controls the operability controls on the UI interface according to the user's pressure operation on the display screen 1305. The operability controls include at least one of a button control, a scroll bar control, an icon control, and a menu control.

[0169] The optical sensor 1313 is used to collect the ambient light intensity. In one embodiment, the processor 1301 can control the display brightness of the display screen 1305 according to the ambient light intensity collected by the optical sensor 1313. Optionally, when the ambient light intensity is high, the display brightness of the display screen 1305 is increased; when the ambient light intensity is low, the display brightness of the display screen 1305 is decreased. In another embodiment, the processor 1301 can also dynamically adjust the shooting parameters of the camera assembly 1306 according to the ambient light intensity collected by the optical sensor 1313.

[0170] The proximity sensor 1314, also called a distance sensor, is disposed on the front panel of the terminal 1300. The proximity sensor 1314 is used to collect the distance between the user and the front of the terminal 1300. In one embodiment, when the proximity sensor 1314 detects that the distance between the user and the front of the terminal 1300 is gradually decreasing, the processor 1301 controls the display screen 1305 to switch from the screen-on state to the screen-off state; when the proximity sensor 1314 detects that the distance between the user and the front of the terminal 1300 is gradually increasing, the processor 1301 controls the display screen 1305 to switch from the screen-off state to the screen-on state.

[0171] Those skilled in the art will understand that Fig.13 The structure shown in the figure does not constitute a limitation on the terminal 1300, and the terminal 1300 may include more or less components than those shown in the figure, or combine some components, or adopt a different component arrangement.

[0172] The embodiment of the present application further provides a computer-readable storage medium, in which at least one computer program is stored. The at least one computer program is loaded and executed by a processor to implement the offset speed determination method of the above embodiment.

[0173] The embodiment of the present application further provides a computer program product, including a computer program, wherein the computer program is loaded and executed by a processor to implement the offset velocity determination method as described in the above embodiment.

[0174] A person skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware or by instructing related hardware through a program. The above program may be stored in a computer-readable storage medium, and the above storage medium may be a read-only memory, a disk or an optical disk, etc.

[0175] The above are only optional embodiments of the embodiments of the present application and are not intended to limit the embodiments of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A method for determining an offset velocity, characterized in that: The method comprises: For imaging points in the first stratum, prestack depth migration is performed on seismic data of the imaging points to obtain a plurality of first common imaging point gathers, where the first common imaging point gathers are used to represent amplitude values ​​of the seismic data at different depths underground; When the straightness of the event axis of each first common imaging point gather is not less than a preset straightness, a plurality of first migration velocities are interpolated respectively to obtain a plurality of second migration velocities, wherein the first migration velocities are used to perform prestack depth migration on the seismic data of the imaging point; For any second migration velocity, based on the first target common imaging point gather, a second common imaging point gather is generated, wherein the first target common imaging point gather is a first common imaging point gather generated by a target first migration velocity, the target first migration velocity is a first migration velocity having a minimum difference with the second migration velocity among the plurality of first migration velocities, and the second common imaging point gather is used to reflect a result of prestack depth migration of seismic data of the imaging point by the second migration velocity; A target second offset velocity is determined from the plurality of second offset velocities, the target second offset velocity is determined as the offset velocity of the first formation, and the straightness of the event axis of the second common imaging point gather generated by the target second offset velocity is less than the preset straightness.

2. The method according to claim 1, characterized in that The second common imaging point gather is used to represent the amplitude value of the seismic data at a first depth, where the first depth is the depth of the location where the imaging point is located; The step of generating a second common imaging point gather based on the first target common imaging point gather for any second migration velocity comprises: Obtaining the travel time and target position of the first ray, wherein the first ray is a ray emitted toward the surface at a preset exit angle at the location of the imaging point, the travel time is the time taken for the first ray to exit the surface from the emission, and the target position is the position where the first ray exits the surface; In response to the second ray being successfully emitted, countdown is performed based on the travel time, and the depth reached by the second ray when the travel time is exhausted is determined as a second depth, wherein the second ray is a ray emitted underground at the target position; Determining an amplitude value of the seismic data at the second depth based on the first target common imaging point gather; The amplitude value of the seismic data at the second depth is used as the amplitude value of the seismic data at the first depth.

3. The method according to claim 2, characterized in that The obtaining of the travel time and target position of the first ray includes: Obtain the initial migration velocity of each formation; Based on the preset exit angle and the transmission speed of the first ray in each stratum, the incident angle and the exit angle of the first ray at each stratum interface are determined by the law of refraction, and the transmission speed of the first ray in each stratum is the initial migration speed of each stratum; The travel time of the first ray and the target position are determined based on the transmission speed of the first ray in each stratum, the incident angle and the exit angle of the first ray at each stratum interface, and the first depth.

4. The method according to claim 2, characterized in that: The determining the amplitude value of the seismic data at the second depth based on the first target common imaging point gather comprises: In the case where the first target common imaging point gather has a depth sampling point at the second depth, using the amplitude value of the depth sampling point as the amplitude value of the seismic data at the second depth; In the case that there is or is not a depth sampling point in the first target common imaging point gather at the second depth, the amplitude value of at least one adjacent depth sampling point at the second depth is interpolated to obtain the amplitude value of the seismic data at the second depth.

5. The method according to claim 1, characterized in that The method further comprises: Acquire an initial velocity model, wherein the initial velocity model is used to represent the relationship between the depth of the formation and the initial migration velocity of the formation; determining an initial migration velocity of the first formation based on the initial velocity model; Based on the initial offset speed, the plurality of first offset speeds are generated within a preset speed range according to a generation step length, where the generation step length is used to represent a difference between two adjacent first offset speeds.

6. The method according to claim 5, characterized in that The method further comprises: Performing time domain velocity analysis on the seismic data of the imaging point to obtain a time domain velocity field, wherein the time domain velocity field is used to represent the relationship between the transmission time of the seismic data in each stratum and the offset velocity of each stratum; Performing prestack time migration on the seismic data of the imaging point to obtain a time domain migration profile, wherein the time domain migration profile is used to divide multiple underground strata and determine the depth of each stratum; The initial velocity model is constructed based on the time-domain velocity field and the time-domain migration profile.

7. The method according to claim 1, characterized in that The method of interpolating a plurality of first migration velocities respectively to obtain a plurality of second migration velocities when the straightness of the event axis of each first common imaging point gather is not less than a preset straightness comprises: In the case where the straightness of the event axis of each of the first common imaging point gathers is not less than the preset straightness, determining a second target common imaging point gather, wherein the second target common imaging point gather is the first common imaging point gather having the smallest difference between the straightness of the event axis and the preset straightness; Determining a third migration velocity based on the second target common imaging point gather, where the third migration velocity is the first migration velocity for generating the second target common imaging point gather; The third offset speed is interpolated within a preset speed range according to an interpolation interval to obtain the plurality of second offset speeds.

8. The method according to claim 1, characterized in that The method further comprises: In response to obtaining the migration velocity of the first formation, the migration velocity of the second formation is determined based on a plurality of common imaging point gathers of imaging points in the second formation, the second formation being a layer below the first formation.

9. A device for determining an offset velocity, characterized in that: The device comprises: A migration module, for performing prestack depth migration on seismic data of imaging points in a first stratum to obtain a plurality of first common imaging point gathers, wherein the first common imaging point gathers are used to represent amplitude values ​​of the seismic data at different depths underground; An interpolation module, configured to interpolate a plurality of first migration velocities respectively to obtain a plurality of second migration velocities when the straightness of the event axis of each first common imaging point gather is not less than a preset straightness, wherein the first migration velocities are used to perform prestack depth migration on the seismic data of the imaging point; A first generating module is configured to generate a second common imaging point gather based on a first target common imaging point gather for any second migration velocity, wherein the first target common imaging point gather is a first common imaging point gather generated by a target first migration velocity, the target first migration velocity is a first migration velocity having a minimum difference with the second migration velocity among the plurality of first migration velocities, and the second common imaging point gather is used to reflect a result of prestack depth migration of seismic data of the imaging point by the second migration velocity; The first determination module is configured to determine a target second offset velocity from the plurality of second offset velocities, determine the target second offset velocity as the offset velocity of the first formation, and the straightness of the event axis of the second common imaging point gather generated by the target second offset velocity is less than the preset straightness.

10. A terminal, characterized in that: The terminal comprises a processor and a memory, wherein at least one computer program is stored in the memory, and the at least one computer program is loaded and executed by the processor to implement the offset velocity determination method according to any one of claims 1 to 8.

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