Method and device for prestack depth migration using imaging grid parameter iteration

Abstract

The present disclosure relates to a method and device for pre-stack depth migration using imaging grid parameter iteration, and relates to the technical field of seismic data processing, wherein the method for pre-stack depth migration using imaging grid parameter iteration includes: using the acquired depth domain imaging grid parameters to perform pre-stack depth migration on the gather data to obtain the result gather; using the result gather and the depth domain imaging grid parameters to update the depth domain layer velocity model; determining the depth error of the result gather and the logging data at the same layer; judging whether the result gather and the depth error meet the preset criteria; if so, outputting the result gather and the updated depth domain layer velocity model; otherwise repeating the above process until the result gather and the depth error meet the preset criteria. This solves the problem that the depth domain layer velocity model obtained after depth migration through the wave equation in the past is inaccurate and cannot meet the needs of precise exploration, resulting in the inability to accurately image the real underground structure in the future.

Description

Technical Field

[0001] The present disclosure relates to the technical field of seismic data processing, and in particular to a method and a device for pre-stack depth migration using imaging grid parameter iteration. Background Art

[0002] Migration is an important step in seismic data processing. It can "reset" the true reflection position of the underground structure and obtain the processing results with the smallest error with the well data structure depth, providing accurate migration results data for subsequent structural map production and other seismic reservoir prediction methods. Migration is divided into two categories in terms of methods: time migration and depth migration. Time migration uses travel time to describe the propagation effect of reflection waves, which can only approximately reflect the kinematic characteristics of seismic waves. Depth migration uses wave equations to accurately describe the wave propagation process, which not only reflects the kinematic characteristics of seismic waves but also contains dynamic laws. Therefore, depth migration can describe and process the imaging problems of complex wave fields.

[0003] However, the accuracy of the depth domain layer velocity model obtained by depth migration through wave equation has not been able to meet the needs of precise exploration. It is difficult to obtain an accurate depth domain layer velocity model directly through surface seismic. Without an accurate layer velocity model, it is impossible to accurately image the real underground structure. The migration technology with a complete theoretical basis is difficult to achieve good processing results due to the uncertainty of the velocity model. Summary of the invention

[0004] The present disclosure proposes a technical solution of a method and device for pre-stack depth migration using imaging grid parameter iteration, and performs multiple pre-stack depth migrations on gather data through imaging grid parameter iteration, and then iterates and updates the depth domain layer velocity model through the resultant gathers obtained after the migration, and finally obtains an accurate depth domain layer velocity model. This solves the problem that the depth domain layer velocity model obtained after depth migration through the wave equation is inaccurate and cannot meet the needs of precise exploration, resulting in the inability to accurately image the real underground structure in the future.

[0005] According to one aspect of the present disclosure, a method for performing prestack depth migration using imaging grid parameter iteration is provided, comprising: step S101: acquiring gather data, depth domain layer velocity model, logging data and depth domain imaging grid parameters of a work area, performing prestack depth migration on the gather data using the depth domain imaging grid parameters to obtain a result gather;

[0006] Step S102: updating the depth domain layer velocity model using the resultant gather and the depth domain imaging grid parameters;

[0007] Step S103: after updating the depth domain layer velocity model, the depth error between the two at the same layer is determined according to the resultant gather and the logging data;

[0008] Step S104: obtaining a preset criterion, and determining whether the resultant gather and the depth error meet the preset criterion; if not, repeating steps S101 to S104 until the resultant gather and the depth error meet the preset criterion;

[0009] Step S105: If satisfied, output the resultant gather and the updated depth domain layer velocity model.

[0010] Preferably, before acquiring the depth domain imaging grid parameters, it is necessary to determine the depth domain imaging grid parameters, and the determination method thereof includes:

[0011] Obtain the minimum velocity, maximum frequency, maximum imaging depth and stratigraphic velocity of the work area;

[0012] The depth domain imaging grid parameters are determined according to the minimum velocity, maximum frequency, maximum imaging depth and stratum velocity through an imaging grid parameter calculation formula.

[0013] Preferably, the method for determining the depth domain imaging grid parameters further comprises:

[0014] Obtaining a first setting value and a second setting value;

[0015] If the tomographic result smoothing parameter of the depth domain imaging grid parameter has a value less than the first set value in the first direction and the second direction, the tomographic result smoothing parameter value in the first direction and the second direction is the first set value; wherein the first direction and the second direction may form a plane;

[0016] If the tomography result smoothing parameter of the depth domain imaging grid parameter has a value in the third direction that is smaller than the second set value, the tomography result smoothing parameter in the third direction is the second set value.

[0017] Preferably, before the first use of the resultant gathers to update the depth domain layer velocity model, the method further includes:

[0018] The method of performing minimum value replacement filling on the depth domain layer velocity model comprises:

[0019] Get the minimum speed of the work area;

[0020] The depth-domain layer velocity model is filled with minimum value replacement using the minimum velocity.

[0021] Preferably, the method for updating the depth domain layer velocity model using the result gather and the depth domain imaging grid parameters comprises:

[0022] The residual depth difference on the resultant gather is picked up, and the depth domain layer velocity model is updated according to the residual depth difference.

[0023] Preferably, the preset criteria include:

[0024] The event axes on the resultant gather are flattened, and the depth error is less than or equal to a predetermined construction accuracy.

[0025] Preferably, the event axes on the resultant gather are flattened as follows:

[0026] The residual depth difference of the resultant gather is obtained. If the distance between the residual depth difference and the zero value in the residual spectrum of the resultant gather is within a predetermined range, the event axis of the resultant gather is flattened.

[0027] Preferably, the imaging grid parameter calculation formula includes:

[0028] Depth imaging grid step size in X / Y / Z directions:

[0029]

[0030] Where: V goal is the formation velocity, V min is the minimum speed, f max is the maximum frequency;

[0031] Offset speed X / Y / Z grid length:

[0032]

[0033] Where: X image , Y image , Z image is the depth imaging grid step size in the X / Y / Z directions;

[0034] Traveltime calculates the step length in the X / Y / Z directions:

[0035]

[0036] Where: H is the maximum imaging depth, Z image is the depth imaging grid step size in the Z direction;

[0037] Target layer speed X / Y / Z three-directional resolution:

[0038]

[0039] Where: H is the maximum imaging depth;

[0040] Tomographic inversion calculation step size in X / Y / Z directions:

[0041]

[0042] Where: H is the maximum imaging depth;

[0043] Three-directional smoothing parameters of tomography results:

[0044]

[0045] Where: The X / Y / Z resolution of the target layer velocity, Tomo X 、Tomo Y 、Tomo Z They are the step sizes in the X / Y / Z directions of tomographic inversion.

[0046] Preferably, the method for determining the depth error of the two at the same layer based on the result gather and the logging data includes:

[0047] The depth error between the resultant gather and the well logging data at the same layer is calculated using a depth error calculation formula;

[0048] Wherein, the depth error calculation formula includes:

[0049]

[0050] Where: H is the depth of the target layer, H PSDM is the imaging depth of the target layer depth migration, H well The depth at which the target well data is read.

[0051] According to one aspect of the present disclosure, there is provided an apparatus for performing prestack depth migration using imaging grid parameter iteration, comprising: an acquisition unit for acquiring gather data, depth domain layer velocity model, logging data, depth domain imaging grid parameters and preset criteria;

[0052] A prestack depth migration unit, used for performing prestack depth migration on the gather data by using the depth domain imaging grid parameters to obtain a resultant gather;

[0053] A model updating unit, used for updating the depth domain layer velocity model using the resultant gather;

[0054] A depth error determination unit is used to determine the depth error of the two at the same layer according to the resultant gather and the logging data after updating the depth domain layer velocity model;

[0055] The judgment unit is used to judge whether the resultant track gather and the depth error meet the preset criteria. If so, the resultant track gather and the updated depth domain layer velocity model are output; otherwise, the acquisition unit, the prestack depth migration unit, the model updating unit, the depth error determination unit and the judgment unit are repeatedly executed until the resultant track gather and the depth error meet the preset criteria.

[0056] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.

[0057] Further features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The drawings herein are incorporated into the specification and constitute a part of the specification. These drawings illustrate embodiments consistent with the present disclosure and are used to illustrate the technical solutions of the present disclosure together with the specification.

[0059] Figure 1 A flow chart showing a method for performing prestack depth migration using imaging grid parameter iteration according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0060] Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0061] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0062] The term "and / or" herein is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the term "at least one" herein represents any combination of at least two of any one or more of a plurality of. For example, including at least one of A, B, and C can represent including any one or more elements selected from the set consisting of A, B, and C.

[0063] In addition, in order to better illustrate the present disclosure, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present disclosure can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present disclosure.

[0064] Figure 1 A flow chart showing a method for performing prestack depth migration using imaging grid parameter iteration according to an embodiment of the present disclosure is shown. Figure 1 As shown, a method for pre-stack depth migration using imaging grid parameter iteration includes: step S101: acquiring gather data, depth domain layer velocity model, logging data and depth domain imaging grid parameters of a work area, and performing pre-stack depth migration on the gather data using the depth domain imaging grid parameters to obtain a resultant gather; step S102: updating the depth domain layer velocity model using the resultant gather and the depth domain imaging grid parameters; step S103: after updating the depth domain layer velocity model, determining the depth error of the resultant gather and the logging data at the same layer; step S104: acquiring a preset criterion, and judging whether the resultant gather and the depth error meet the preset criterion; if not, repeating steps S101 to S104 until the resultant gather and the depth error meet the preset criterion; step S105: if satisfied, outputting the resultant gather and the updated depth domain layer velocity model. This is to solve the problem that the depth domain layer velocity model obtained after depth migration through the wave equation in the past is inaccurate and cannot meet the needs of precise exploration, resulting in the subsequent inability to accurately image the real underground structure.

[0065] The method for prestack depth migration using imaging grid parameter iteration provided by an embodiment of the present invention specifically includes the following steps:

[0066] Step S101: acquiring gather data, depth domain layer velocity model, logging data and depth domain imaging grid parameters of a work area, and performing prestack depth migration on the gather data using the depth domain imaging grid parameters to obtain a result gather.

[0067] In the present disclosure, before the depth domain layer velocity model is updated for the first time using the resultant data set, it also includes: performing minimum value replacement filling on the depth domain layer velocity model, and the method includes: obtaining the minimum velocity of the work area; and performing minimum value replacement filling on the depth domain layer velocity model using the minimum velocity.

[0068] In the embodiment of the present disclosure, before the first pre-stack depth migration is performed, the depth domain layer velocity model obtained is the depth domain layer velocity model initially established based on the seismic data. min is the velocity of the first arrival of a typical single shot. The first arrival velocity is the velocity obtained by the time when each detector receives the seismic signal and the distance between the detector and the excitation shot point.

[0069] The method for replacing and filling the minimum value of the depth domain layer velocity model with the minimum velocity comprises: judging whether the shallow layer velocity of the depth domain layer velocity model is less than the minimum velocity, and if so, replacing the shallow layer velocity less than the minimum velocity with the minimum velocity. If the typical single shot first arrival velocity, that is, the minimum velocity, is 2000 m / s, then replacing the shallow layer velocity less than 2000 m / s of the depth domain layer velocity model with 2000 m / s.

[0070] For the initial depth domain layer velocity model, the shallow layer velocity should be greater than the minimum velocity V min ,When the shallow velocity has a minimum or abnormally small value, it is necessary to replace and fill the shallow velocity with the minimum value to make it larger than the first arrival velocity of a typical single shot.

[0071] In the present disclosure, before obtaining the depth domain imaging grid parameters, it is necessary to determine the depth domain imaging grid parameters, and the determination method thereof includes: obtaining the minimum velocity, maximum frequency, maximum imaging depth and stratigraphic layer velocity of the work area; and determining the depth domain imaging grid parameters through an imaging grid parameter calculation formula according to the minimum velocity, maximum frequency, maximum imaging depth and stratigraphic layer velocity.

[0072] In the embodiment of the present disclosure, the maximum frequency f max is the maximum frequency at -20 dB in the seismic data; the maximum imaging depth is the maximum burial depth, and the maximum burial depth is the target burial depth of the well logging data in the work area; the formation velocity V goal is the formation velocity at the maximum imaging depth recorded by logging data.

[0073] In the present disclosure, the imaging grid parameter calculation formula includes:

[0074] (1) Depth imaging grid step size in X / Y / Z directions:

[0075]

[0076] Where: V goal is the formation velocity, V min is the minimum speed, f max is the maximum frequency.

[0077] (2) Offset speed X / Y / Z grid length:

[0078]

[0079] Where: X image , Y image , Z image It is the depth imaging grid step size in the X / Y / Z directions.

[0080] (3) Traveltime calculates the step length in the X / Y / Z directions:

[0081]

[0082] Where: H is the maximum imaging depth, Z image is the depth imaging grid step size in the Z direction.

[0083] (4) Target layer velocity resolution in three directions: X / Y / Z:

[0084]

[0085] Where: H is the maximum imaging depth.

[0086] (5) Calculation step size of tomographic inversion in three directions: X / Y / Z:

[0087]

[0088] Where: H is the maximum imaging depth.

[0089] (6) Three-directional smoothing parameters of tomography results:

[0090]

[0091] Where: The X / Y / Z resolution of the target layer velocity, Tomo X 、Tomo Y 、Tomo Z They are the step sizes in the X / Y / Z directions of tomographic inversion.

[0092] In the embodiment of the present disclosure, if the minimum speed V min The value is 1600m / s, the maximum frequency f max The value is 70Hz, the maximum burial depth, i.e. the maximum imaging depth H, is 2000m, and the formation velocity is 3500m / s. Substituting into the above grid parameter calculation formula, the first round, i.e. the first calculation of 6 sets of depth domain imaging grid parameters, is obtained as follows:

[0093] (1) The first round of depth imaging grid step size in the three directions of X / Y / Z:

[0094]

[0095] (2) First round of offset speed X / Y / Z grid length:

[0096]

[0097] (3) Traveltime calculates the step length in the X / Y / Z directions during the first round of travel:

[0098]

[0099] (4) First round of target layer velocity X / Y / Z three-dimensional resolution:

[0100]

[0101] (5) Calculation step size in the first round of tomographic inversion in the three directions of X / Y / Z:

[0102]

[0103] (6) Smoothing parameters of the first round of tomography results in three directions: X / Y / Z:

[0104]

[0105]

[0106] According to the depth domain imaging grid parameter values ​​calculated above, the first pre-stack depth migration is performed on the gather data. The depth imaging grid step in the X / Y / Z directions obtained by formula (1) is used to perform depth migration imaging on the gather data. The migration velocity grid length in the X / Y / Z directions obtained by formula (2) is used to determine the size of the gather data velocity grid update. The travel time of the gather data is calculated using the step in the X / Y / Z directions obtained by formula (3), thereby finally obtaining the result gather.

[0107] Step S102: using the resultant gather and the depth domain imaging grid parameters to update the depth domain layer velocity model.

[0108] In the present disclosure, the method for updating the depth domain layer velocity model using the resultant gather and the depth domain imaging grid parameters includes: picking up the residual depth difference on the resultant gather, and updating the depth domain layer velocity model by the residual depth difference.

[0109] In an embodiment of the present disclosure, a method for picking up the residual depth difference on the resultant gather and updating the depth domain layer velocity model by the residual depth difference includes:

[0110] The velocity value of each point on the propagation path is updated by back-projecting the difference between the measured data travel time and the predicted data travel time, and the following equation is established:

[0111]

[0112] Where: S is slowness (the inverse of velocity change), δs is the slowness correction, L is the offset velocity ray path, L' is the true ray path; dl is the differential along the ray path. Among them, the measured data travel time is the imaging depth of the target layer of the result gather, and the predicted data travel time is the actual imaging point of the target layer at the actual underground position.

[0113] The formula is transformed into the following discrete form:

[0114]

[0115] Where N is the number of grids, Δt is the discrete form of the residual delay, and Δs i is the slowness perturbation of the ith grid point, l i is the ray length of the ray in the i-th grid.

[0116] In this way, each picked residual depth difference will correspond to a residual time difference, that is, to a ray path, and all ray paths can form a large sparse matrix:

[0117] (9) L·ΔS=ΔT;

[0118] Where: L is the ray length, △S is the matrix of the slowness perturbation s, and △T is the matrix of the residual time difference △t.

[0119] By solving the least squares solution with the conjugate gradient method, the slowness variation of each grid can be obtained, and the variation is applied to the known depth domain velocity model, that is:

[0120] S new =S old +ΔS;

[0121] Where: S new is the updated slowness; S old is the actual slowness used in this round of migration; △S is the slowness disturbance obtained in this round.

[0122] By solving the matrix, the updated depth domain velocity model of the residual depth difference can be obtained.

[0123] In an embodiment of the present disclosure, a method for updating a depth domain layer velocity model using depth domain imaging grid parameters comprises: using the target layer velocity X / Y / Z three-directional resolution obtained by formula (4) and the tomographic inversion X / Y / Z three-directional calculation step obtained by formula (5) in the six groups of grid parameters calculated by the grid parameter calculation formula to update the velocity grid size of the depth domain layer velocity model; and using the tomographic result three-directional smoothing parameters obtained by formula (6) to adjust the velocity trend of the depth domain layer velocity model.

[0124] The initial depth domain layer velocity model is updated by using the residual depth difference picked up by the result gather and the calculated depth domain imaging grid parameters to obtain an updated depth domain layer velocity model.

[0125] Step S103: After updating the depth domain layer velocity model, the depth error between the resultant gather and the logging data at the same layer is determined according to the resultant gather and the logging data.

[0126] In the present disclosure, the method for determining the depth error of the resultant gather and the logging data at the same layer according to the resultant gather and the logging data comprises: calculating the depth error of the resultant gather and the logging data at the same layer using a depth error calculation formula; wherein the depth error calculation formula comprises:

[0127]

[0128] Where: H is the depth of the target layer, H PSDM is the imaging depth of the target layer depth migration, H well The depth at which the target well data is read.

[0129] In the embodiment of the present disclosure, if H PSDM The value is 2050m, H well If the value is 50m, then substituting it into the above depth error calculation formula will give the depth error:

[0130]

[0131] Step S104: Obtain a preset criterion and determine whether the resultant gather and the depth error meet the preset criterion; if not, repeat steps S101 to S104 until the resultant gather and the depth error meet the preset criterion.

[0132] Step S105: If satisfied, output the resultant gather and the updated depth domain layer velocity model.

[0133] In the present disclosure, the preset criteria include: the event axis on the resultant gather is flattened, and the depth error is less than or equal to a predetermined construction accuracy.

[0134] In the present disclosure, the in-phase axis flattening on the resultant track gather is: obtaining the residual depth difference of the resultant track gather, and if the distance between the residual depth difference and the zero value in the residual spectrum of the resultant track gather is within a predetermined range, the in-phase axis of the resultant track gather is flattened.

[0135] In the embodiment of the present disclosure, by quality controlling the residual depth difference of the resultant gather, it can be determined whether the resultant gather is flattened. If the residual depth difference of the resultant gather coincides with the zero value position in its residual spectrum or the distance between the residual depth difference and the zero value is within a predetermined range, it means that the resultant gather is completely flattened. The predetermined range is 1% of the velocity change. The velocity change is calculated as follows: (v2-v1) / v1, where V1 is the target layer velocity of the depth domain layer velocity model, and V2 is the velocity picked up according to the residual depth difference of the resultant gather.

[0136] In addition to the requirement that the event axes of the resultant gathers are completely flattened, it is also necessary to ensure that the depth error between the resultant gathers and the logging data in the same layer is less than or equal to the predetermined structural accuracy, where the predetermined structural accuracy is 3‰.

[0137] Usually, after the first round of pre-stack depth migration, the depth error between the resultant gather and the logging data is much greater than the predetermined structural accuracy required for interpretation. If the calculated depth error is 0.025, it means that the preset criteria cannot be met, and the process of steps S101 to S104 needs to be repeated. Each execution of steps S101 to S104 is a round of iterative update. The second round of iterative update will recalculate 6 sets of depth domain imaging grid parameters based on the depth domain layer velocity model parameters updated in the previous round, complete the second round of pre-stack depth migration and update the depth domain layer velocity model, minimize the residual time difference of the resultant gather, calculate the well depth error again, and determine whether it is less than or equal to the predetermined structural accuracy. By analogy, the imaging grid parameters are gradually reduced to obtain more refined depth domain layer velocity model tomography results, perform multiple rounds of iterative pre-stack depth migration on the gather data, gradually eliminate the residual time difference of the gather data, reduce the well structural depth error, and finally obtain pre-stack depth migration results that meet geological requirements. After many experiments, it is concluded that, generally after 3 to 4 rounds of iterative updates, the event axes of the resultant gathers are completely flattened and the depth error obtained by calculation will be less than 3‰. At this time, the resultant gathers after the last round of iterative migration and the updated depth domain layer velocity model can be output.

[0138] Except for the first round of updating the depth domain layer velocity model, in which the initial depth domain layer velocity model is updated, each subsequent round of iterative updating is to update the updated depth domain layer velocity model obtained in the previous round.

[0139] In the second round of iterative update, based on the depth domain layer velocity model obtained in the previous round, that is, the first iterative update, combined with the known maximum frequency, minimum velocity, maximum imaging depth and target layer velocity in the first round, 6 sets of depth domain imaging grid parameters are calculated through the grid parameter calculation formula:

[0140] (1) The second round of depth imaging grid step size in the X / Y / Z directions:

[0141]

[0142] (2) Grid length in three directions of the second round of offset velocity:

[0143]

[0144] (3) During the second round of travel, the travel time is used to calculate the step lengths in three directions:

[0145]

[0146] (4) Second round of target layer velocity three-directional resolution:

[0147]

[0148] (5) Calculation step length of three directions for the second round of tomographic inversion:

[0149]

[0150] (6) Three-directional smoothing parameters of the second round of tomography results:

[0151]

[0152] Compared with the first round of iterative update, the grid of the second round of iterative tomography inversion calculation is smaller, the smoothing parameter of the inversion result is also smaller, and the inversion result accuracy is higher. The 6 sets of depth domain imaging grid parameters calculated in the second round are used to perform prestack depth migration on the result gather and update the depth domain layer velocity model, calculate the well depth error, and judge whether it is less than or equal to the predetermined structural accuracy. If not, repeat steps S101 to 4 to calculate the 6 sets of depth domain imaging grid parameters of the third round as follows:

[0153] (1) The third round of depth imaging grid step size in the X / Y / Z directions:

[0154]

[0155] (2) Grid length in three directions of the third round of offset speed:

[0156]

[0157] (3) During the third round of travel, the travel time is used to calculate the step lengths in three directions:

[0158]

[0159] (4) The third round of target layer velocity three-directional resolution:

[0160]

[0161] (5) Calculation step length in three directions of the third round of tomographic inversion:

[0162]

[0163] (6) Three-directional smoothing parameters of the third round of tomography results:

[0164]

[0165] Compared with the depth domain imaging grid parameters obtained in the second round, the grid of the third round of iterative tomographic inversion calculation is smaller, the smoothing parameter of the inversion result is also smaller, and the inversion result accuracy is higher; the depth domain imaging grid parameters obtained in this step are used to perform the third round of prestack depth migration, and the depth domain layer velocity model is updated on the resultant gather with the purpose of flattening the event axis and eliminating the residual time difference; the depth error e of the prestack depth migration result is calculated again using the known well data to examine whether the event axis on the resultant gather is completely flattened, and whether the well depth error e is less than the structural accuracy of 3‰ required for interpretation. If all of them are satisfied, the calculation is stopped and the updated depth domain layer velocity model and the resultant gather are output; if not, the fourth round of iterative update is continued.

[0166] In the present disclosure, the method for determining the depth domain imaging grid parameter further includes: acquiring a first setting value and a second setting value; if the tomography result smoothing parameter of the depth domain imaging grid parameter has a value less than the first setting value in the first direction and the second direction, the tomography result smoothing parameter value in the first direction and the second direction is the first setting value; wherein the first direction and the second direction may form a plane; if the tomography result smoothing parameter of the depth domain imaging grid parameter has a value less than the second setting value in the third direction, the tomography result smoothing parameter in the third direction is the second setting value.

[0167] In the embodiment of the present disclosure, after obtaining 6 sets of depth domain imaging grid parameters in each round of calculation, it is also necessary to determine whether the values ​​of the three-directional smoothing parameters of the tomographic results in formula (6) in the grid parameter calculation formula are less than the first set value in the first direction and the second direction, and whether the value of the third direction is less than the second set value, wherein the first set value is 5, the second set value is 3, the first direction is the X direction, the second direction is the Y direction, and the third direction is the Z direction. That is to say, in the calculated tomographic result smoothing parameters, the values ​​in the X and Y directions must be greater than or equal to 5, and the value in the Z direction must be greater than or equal to 3. If the values ​​of the smoothing parameters in the X and Y directions are less than 5, and the value of the smoothing parameter in the Z direction is less than 3, velocity distortion will occur in the depth domain layer velocity model.

[0168] If the well depth error e is still greater than the construction accuracy after the third round of iterative update, the fourth round of iterative update is performed to calculate 6 sets of depth domain grid imaging parameters:

[0169] (1) The fourth round of depth imaging grid step size in the X / Y / Z directions:

[0170]

[0171] (2) Grid length in three directions of the fourth round of offset speed:

[0172]

[0173] (3) During the fourth round of travel, Traveltime calculates the step lengths in three directions:

[0174]

[0175] (4) Resolution of target layer velocity in three directions in the fourth round:

[0176]

[0177] (5) Calculation step length of the fourth round of tomographic inversion in three directions:

[0178]

[0179] (6) Three-directional smoothing parameters of the fourth round of tomography results:

[0180]

[0181] Among them, if the values ​​of the three-directional smoothing parameter values ​​of the tomography results of the fourth round of calculation are less than 5 in the X and Y directions, they will be replaced by 5; if the value in the Z direction is less than 3, it will be replaced by 3.

[0182] The fourth round of prestack depth migration is performed on the gather data using the fourth round of depth domain imaging grid parameters to obtain the resultant gathers. The depth domain layer velocity model is updated again using the resultant gathers and the depth domain imaging grid parameters, and the well depth error e is calculated. After four rounds of iterative updates, the event axes on the resultant gathers have been completely flattened, and the well depth error e is less than 3‰ of the structural accuracy. All operations are completed, and the depth domain layer velocity model and the resultant gathers after the last round of updates can be directly output.

[0183] The execution subject of the method for performing prestack depth migration by iterative imaging grid parameters may be a device for performing prestack depth migration by iterative imaging grid parameters. For example, the method for performing prestack depth migration by iterative imaging grid parameters may be executed by a terminal device or a server or other processing device, wherein the terminal device may be a user equipment (UE), a mobile device, a user terminal, a terminal, a cellular phone, a cordless phone, a personal digital assistant (PDA), a handheld device, a computing device, a vehicle-mounted device, a wearable device, etc. In some possible implementations, the method for performing prestack depth migration by iterative imaging grid parameters may be implemented by a processor calling computer-readable instructions stored in a memory.

[0184] Those skilled in the art will appreciate that, in the above method of specific implementation, the order in which the steps are written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of the steps should be determined by their functions and possible internal logic.

[0185] The present disclosure also proposes a device for performing prestack depth migration using imaging grid parameter iteration, comprising: an acquisition unit, used to acquire track data, a depth domain layer velocity model, logging data, depth domain imaging grid parameters and preset criteria; a prestack depth migration unit, used to perform prestack depth migration on the track data using the depth domain imaging grid parameters to obtain a result track; a model updating unit, used to update the depth domain layer velocity model using the result track; a depth error determination unit, used to determine the depth error of the result track and the logging data at the same layer after updating the depth domain layer velocity model; a judgment unit, used to judge whether the result track and the depth error meet the preset criteria, and if so, output the result track and the updated depth domain layer velocity model; otherwise, repeatedly execute the acquisition unit, prestack depth migration unit, model updating unit, depth error determination unit and judgment unit until the result track and the depth error meet the preset criteria.

[0186] In some embodiments, the functions of the device provided by the embodiments of the present disclosure or the units and modules included therein can be used to execute the method of performing pre-stack depth migration using imaging grid parameter iteration described in the above method embodiments. The specific implementation thereof can refer to the description of the above method embodiments and will not be repeated here for the sake of brevity.

[0187] The core of the present invention is to take geological requirements as the starting point, accurately calculate the optimal depth domain 6-group imaging grid parameters, obtain the resultant gathers by performing pre-stack depth migration on the gather data, and update the depth domain layer velocity model using the resultant gathers and depth domain imaging grid parameters. If the resultant gathers do not meet the minimum requirements of flattening the event axis and the well structure error (depth error) being less than the structural accuracy, then a more refined depth domain layer velocity model tomography result is obtained by reducing the depth domain imaging grid parameters, and multiple rounds of iterative pre-stack depth migration are performed to eliminate the residual time difference of the gather data round by round, and reduce the well structure depth error round by round, and finally obtain the resultant gathers and depth domain layer velocity model that meet the geological requirements, that is, the pre-stack depth migration results. According to the final pre-stack depth migration results, the real underground structure can be accurately imaged.

[0188] It can be understood that the above-mentioned various method embodiments mentioned in the present disclosure can be combined with each other to form a combined embodiment without violating the principle logic. Due to space limitations, the present disclosure will not go into details.

[0189] Those skilled in the art will appreciate that, in the above method of specific implementation, the order in which the steps are written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of the steps should be determined by their functions and possible internal logic.

[0190] The embodiment of the present disclosure also provides a computer-readable storage medium, on which computer program instructions are stored, and when the computer program instructions are executed by a processor, the above method is implemented. The computer-readable storage medium may be a non-volatile computer-readable storage medium.

[0191] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for prestack depth migration using imaging grid parameter iteration, characterized in that: include: Step S101: acquiring gather data, depth domain layer velocity model, logging data and depth domain imaging grid parameters of a work area, and performing prestack depth migration on the gather data using the depth domain imaging grid parameters to obtain a result gather; Before acquiring the depth domain imaging grid parameters, it is necessary to determine the depth domain imaging grid parameters, and the determination method thereof includes: Obtain the minimum velocity, maximum frequency, maximum imaging depth and stratigraphic velocity of the work area; Determine the depth domain imaging grid parameters by using the imaging grid parameter calculation formula according to the minimum velocity, maximum frequency, maximum imaging depth and formation velocity; Step S102: updating the depth domain layer velocity model using the resultant gather and the depth domain imaging grid parameters; Step S103: after updating the depth domain layer velocity model, the depth error between the two at the same layer is determined according to the resultant gather and the logging data; Step S104: obtaining a preset criterion, and determining whether the resultant gather and the depth error meet the preset criterion; if not, repeating steps S101 to S104 until the resultant gather and the depth error meet the preset criterion; Step S105: If satisfied, output the resultant gather and the updated depth domain layer velocity model.

2. The method for prestack depth migration using imaging grid parameter iteration according to claim 1, characterized in that: The method for determining the depth domain imaging grid parameters also includes: Obtaining a first setting value and a second setting value; If the tomographic result smoothing parameter of the depth domain imaging grid parameter has a value less than the first set value in the first direction and the second direction, the tomographic result smoothing parameter value in the first direction and the second direction is the first set value; wherein the first direction and the second direction may form a plane; If the tomography result smoothing parameter of the depth domain imaging grid parameter has a value in the third direction that is smaller than the second set value, the tomography result smoothing parameter in the third direction is the second set value.

3. The method for prestack depth migration using imaging grid parameter iteration according to claim 1, characterized in that: Before the first use of the resultant gathers to update the depth domain layer velocity model, the method also includes: The method of performing minimum value replacement filling on the depth domain layer velocity model comprises: Get the minimum speed of the work area; The depth-domain layer velocity model is filled with minimum value replacement using the minimum velocity.

4. The method for prestack depth migration using imaging grid parameter iteration according to claim 1, characterized in that: The method for updating the depth domain layer velocity model using the result gather and the depth domain imaging grid parameters comprises: The residual depth difference on the resultant gather is picked up, and the depth domain layer velocity model is updated according to the residual depth difference.

5. The method for prestack depth migration using imaging grid parameter iteration according to claim 1, characterized in that: The preset criteria include: The event axes on the resultant gather are flattened, and the depth error is less than or equal to a predetermined construction accuracy.

6. The method for prestack depth migration using imaging grid parameter iteration according to claim 5, characterized in that: The event on the result gather is flattened as follows: The residual depth difference of the resultant gather is obtained. If the distance between the residual depth difference and the zero value in the residual spectrum of the resultant gather is within a predetermined range, the event axis of the resultant gather is flattened.

7. The method for prestack depth migration using imaging grid parameter iteration according to claim 1, characterized in that: The imaging grid parameter calculation formula includes: Depth imaging grid step size in X / Y / Z directions: Where: V goal is the formation velocity, V min is the minimum speed, f max is the maximum frequency; Offset speed X / Y / Z grid length: Where: X image , Y image , Z image is the depth imaging grid step size in the X / Y / Z directions; Traveltime calculates the step length in the X / Y / Z directions: TT Z =10·Z image ; Where: H is the maximum imaging depth, Z image is the depth imaging grid step size in the Z direction; Target layer speed X / Y / Z three-directional resolution: Where: H is the maximum imaging depth; Tomographic inversion calculation step size in X / Y / Z directions: Where: H is the maximum imaging depth; Three-directional smoothing parameters of tomography results: Where: The X / Y / Z resolution of the target layer velocity, Tomo X 、Tomo Y 、Tomo Z They are the step sizes in the X / Y / Z directions of tomographic inversion.

8. The method for prestack depth migration using imaging grid parameter iteration according to any one of claims 1 to 7, characterized in that: The method for determining the depth error of the two at the same layer based on the result gather and the logging data includes: The depth error between the resultant gather and the well logging data at the same layer is calculated using a depth error calculation formula; Wherein, the depth error calculation formula includes: Where: H is the depth of the target layer, H PSDM is the imaging depth of the target layer depth migration, H well The depth at which the target well data is read.

9. A device for prestack depth migration using imaging grid parameter iteration, characterized in that: include: An acquisition unit, used to acquire gather data, depth domain layer velocity model, logging data, depth domain imaging grid parameters and preset criteria; A prestack depth migration unit, used for performing prestack depth migration on the gather data by using the depth domain imaging grid parameters to obtain a resultant gather; A model updating unit, used for updating the depth domain layer velocity model using the resultant gather; A depth error determination unit is used to determine the depth error of the two at the same layer according to the resultant gather and the logging data after updating the depth domain layer velocity model; The judgment unit is used to judge whether the resultant track gather and the depth error meet the preset criteria. If so, the resultant track gather and the updated depth domain layer velocity model are output; otherwise, the acquisition unit, the prestack depth migration unit, the model updating unit, the depth error determination unit and the judgment unit are repeatedly executed until the resultant track gather and the depth error meet the preset criteria.

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