Dip angle scanning-based migration imaging profile generation method

Abstract

The invention belongs to the technical field of seismic migration imaging, and particularly relates to a migration imaging profile generation method based on inclination angle scanning. The method comprises the following steps: extracting a dip angle domain common imaging point gather of original seismic data; carrying out superposition imaging on all dip angle domain common imaging point gathers to obtain an initial migration imaging profile; performing dip angle scanning on the initial migration imaging profile to obtain a true stratum dip angle field; according to the true stratum dip angle field and the initial imaging profile, determining a dip angle effective imaging area of the target imaging point, and obtaining a dip angle domain common imaging point gather in the dip angle effective imaging area; and carrying out superposition imaging on the inclination angle domain common imaging point gather in the inclination angle effective imaging area to obtain a final migration imaging section. According to the method, the migration noise of the Gaussian beam depth migration imaging profile is reduced, the signal-to-noise ratio of the Gaussian beam depth migration imaging profile is enhanced, the signal-to-noise ratio of the generated migration imaging profile is higher, the migration imaging profile is more accurate and reliable, and subsequent seismic interpretation processing is facilitated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of seismic migration imaging, and particularly relates to a migration imaging profile generation method based on dip angle scanning. BACKGROUND

[0002] With the gradual increase of exploration and development difficulty, the exploration target begins to shift to complex structure exploration areas such as fracture oil and gas reservoirs and lithologic oil and gas reservoirs. The lateral sudden change of near-surface and middle-deep layer velocity in the complex structure exploration area makes the processing of seismic data more difficult. In order to more accurately perform seismic interpretation, attribute analysis and reservoir prediction, a depth migration imaging method is usually used to construct a prestack migration imaging profile, and a geologist analyzes the underground geological structure according to the related features of the profile.

[0003] At present, common depth migration imaging methods include reverse time migration, Fourier finite difference migration, Kirchhoff migration and Gaussian beam depth migration. The reverse time migration method has the highest imaging accuracy, but the method has low calculation efficiency and consumes large memory; the Fourier finite difference migration method can be applied to both time domain and frequency domain, but its imaging accuracy is low; the Kirchhoff migration method has high calculation efficiency and strong matching ability for irregular observation data, and is widely used in commercial scale production, but it cannot process complex imaging problems in geophysical exploration and cannot meet the fine exploration requirements of target blocks; the Gaussian beam depth migration method not only solves the theoretical defects of Kirchhoff migration, but also inherits its flexibility and high efficiency, and has strong imaging adaptability. Its dependence on the initial depth domain velocity field is also weaker than that of reverse time migration. Therefore, the Gaussian beam depth migration method can be used to construct a prestack migration imaging profile. For example, a Chinese patent application for invention with the publication number CN114002742B discloses an Euler Gaussian beam migration imaging method and device, which uses Gaussian beams to perform migration processing on the shot record to be imaged to obtain a seismic migration profile.

[0004] However, it is found in actual use that various migration noises exist in the Gaussian beam prestack depth migration imaging profile. The reasons for producing these noises are various, for example: 1) the Gaussian beam depth migration method cannot process all the wave arrival information, and the remaining wave arrival information becomes a noise component; 2) using Gaussian beam stacking integral to approximate the Green function to describe the seismic wave field in complex media leads to errors; 3) the Gaussian beam depth migration method cannot eliminate the illumination irregularity caused by irregular observation systems; 4) the signal-to-noise ratio of seismic data is low. The migration noises produced by the above reasons are usually in the form of distorted "smile" interspersed in the real phase axis, resulting in a low signal-to-noise ratio of the obtained imaging profile and a low accuracy of the migration imaging profile. SUMMARY

[0005] The application aims to provide a dip-angle scanning based migration imaging profile generation method to solve the problems of low signal-to-noise ratio and accuracy of the migration imaging profile generated by the existing Gaussian beam depth migration method.

[0006] The application provides a dip-angle scanning based migration imaging profile generation method to solve the above technical problems, comprising the following steps:

[0007] extracting a dip-angle domain common imaging point gather of the original seismic data;

[0008] stacking and imaging all the dip-angle domain common imaging point gathers to obtain an initial migration imaging profile;

[0009] performing dip-angle scanning on the initial migration imaging profile to obtain a true stratigraphic dip-angle field;

[0010] determining a dip-angle effective imaging area of a target imaging point according to the true stratigraphic dip-angle field and the initial imaging profile, and obtaining a dip-angle domain common imaging point gather in the dip-angle effective imaging area;

[0011] stacking and imaging the dip-angle domain common imaging point gather in the dip-angle effective imaging area to obtain a final migration imaging profile.

[0012] Further, the true stratigraphic dip-angle is obtained through a dip-angle scanning formula, and the true stratigraphic dip-angle is arranged in a set order to obtain a true stratigraphic dip-angle field, the dip-angle scanning formula being:

[0013]

[0014] wherein θ is the true stratigraphic dip-angle obtained through the dip-angle scanning, Δx is a horizontal unit length of the initial migration imaging profile, Δz is a vertical unit length of the initial migration imaging profile, and win is a time window used for the dip-angle scanning.

[0015] Further, the dip-angle effective imaging area at the target imaging point is:

[0016]

[0017] wherein θ is the true stratigraphic dip-angle obtained through the dip-angle scanning, is the dip-angle at the target imaging point x0, and β1 and β2 respectively represent the constraint ranges on the left and right sides of the true stratigraphic dip-angle.

[0018] Further, the dip-angle common imaging point gather in the dip-angle effective imaging area is obtained according to the following screening conditions:

[0019]

[0020] wherein, I(x0) is the amplitude value of the dip-angle domain common imaging point gather at the target imaging point x0 in the initial imaging profile, and c is an adjustable coefficient less than 1.

[0021] Further, the calculation formula for the superimposed imaging of the dip-angle domain common imaging point gather in the dip-angle effective imaging area is:

[0022]

[0023] wherein, S final (x0) is the final migration profile at the target imaging point x0, is the dip angle at the target imaging point x0, is the amplitude value of the dip-angle domain common imaging point gather at the target imaging point x0 in the dip-angle effective imaging area.

[0024] Further, the method for extracting the dip-angle domain common imaging point gather of the original seismic data is to calculate the dip angle at the target imaging point according to the original seismic data and the Gaussian beam depth migration method, and then to perform prestack depth migration on the dip angle, thereby obtaining the dip-angle domain common imaging point gather of the original seismic data.

[0025] Further, the calculation formula for the dip angle at the target imaging point is:

[0026]

[0027] wherein, is the dip angle at the target imaging point x0, is the beam propagation angle from the shot point x s , is the beam propagation angle from the receiver x r .

[0028] Further, the calculation formula for the beam propagation angle is:

[0029]

[0030] wherein, angle is the beam propagation angle, p x , p z are the horizontal component and the vertical component of the beam ray parameter respectively, π is the circular constant, and arctan is the inverse tangent calculation function.

[0031] The beneficial effects of the above technical scheme are as follows: compared with the traditional method of directly using the Gaussian beam depth migration method to obtain the migration imaging profile, after obtaining the initial migration imaging profile, the true stratigraphic dip is obtained through dip scanning, the dip effective imaging area of the target imaging point is determined based on the initial migration imaging profile and the true stratigraphic dip data, and the final migration imaging profile is obtained based on the dip domain common imaging point gather in the dip effective imaging area, so that the migration noise of the Gaussian beam depth migration imaging profile is reduced, the signal-to-noise ratio of the Gaussian beam depth migration imaging profile is enhanced, the generated migration imaging profile has a higher signal-to-noise ratio, the migration imaging profile is more accurate and reliable, and the subsequent seismic interpretation processing is facilitated. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The method flowchart for generating the migration imaging profile based on dip scanning in the method embodiment of the application;

[0033] Figure 2 The local angle decomposition diagram of beam imaging at the imaging point in the method embodiment of the application;

[0034] Figure 3 The depth domain migration velocity model schematic diagram of the work area in the embodiment of the application;

[0035] Figure 4 The geophone observation record diagram of the work area single shot number in the embodiment of the application;

[0036] Figure 5 The dip domain common imaging point gather diagram of the work area imaging point in the embodiment of the application;

[0037] Figure 6 The initial migration imaging profile diagram of the work area stack in the embodiment of the application;

[0038] Figure 7 The true stratigraphic dip field diagram obtained by dip scanning of the work area in the embodiment of the application;

[0039] Figure 8 The dip domain common imaging point gather diagram in the dip effective imaging area of the work area imaging point in the embodiment of the application;

[0040] Figure 9 The final migration imaging profile diagram of the work area in the embodiment of the application;

[0041] Figure 10 The local enlarged diagram of the initial migration imaging profile diagram of the work area in the embodiment of the application;

[0042] Figure 11 The local enlarged diagram of the final migration imaging profile diagram of the work area in the embodiment of the application. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clear, the specific embodiments of the present invention are further described below with reference to the accompanying drawings.

[0044] The present invention extracts the dip domain common imaging point gathers from the original seismic data, obtains the initial migration imaging section based on the dip domain common imaging point gathers, obtains the true formation dip through dip scanning, determines the dip effective imaging area of ​​the target imaging point based on the initial migration imaging section and the true formation dip data, and obtains the final migration imaging section based on the dip domain common imaging point gathers within the dip effective imaging area. This enhances the signal-to-noise ratio of the Gaussian beam depth migration imaging section, makes the generated migration imaging section have a higher signal-to-noise ratio, and makes the migration imaging section more accurate and reliable, which is beneficial to subsequent seismic interpretation processing.

[0045] Method Example

[0046] like Figure 1 As shown, the specific process is as follows:

[0047] 1. Extract the dip domain common imaging point gathers of the original seismic data.

[0048] Specifically, the dip domain common imaging point gathers of the original seismic data are extracted based on the Gaussian beam depth migration method. The original seismic data and the Marmousi velocity model are input, and the dip at the target imaging point x0 is calculated using the Gaussian beam depth migration method. Then the inclination Perform pre-stack depth migration processing, and output dip domain common imaging point gathers after all seismic data in the target area are calculated.

[0049] like Figure 2 As shown in the figure, the calculation formula for the inclination angle at the target imaging point x0 is:

[0050]

[0051] in, From the gun point x s The beam spreading angle, is from the detector x r beam spreading angle.

[0052] At the imaging point x0, the beam propagation angle from the shot point and the detector is calculated as:

[0053]

[0054] Among them, p x 、p zare horizontal and vertical components of beam ray parameter, angle is beam propagation angle (angle between ray direction and positive direction of z-axis, positive in counterclockwise direction), π is circular constant, and arctan is inverse tangent calculation function.

[0055] 2. Superimpose and image all the dip-angle domain common imaging point gathers to obtain an initial migration profile.

[0056] 3. Perform dip-angle scanning on the initial migration profile to obtain a true stratigraphic dip-angle field.

[0057] Specifically, the true stratigraphic dip angle at a target imaging point is obtained through a dip-angle scanning formula, and then a true stratigraphic dip-angle field is obtained by arranging in a set order. The dip-angle scanning formula is as follows:

[0058]

[0059] wherein θ is the true stratigraphic dip angle obtained through dip-angle scanning, Δx is a horizontal unit length of the initial migration profile, Δz is a vertical unit length of the initial migration profile, and win is a time window used for dip-angle scanning, generally being a model sampling interval or an integer multiple thereof. The set order refers to a grid order of the subsurface, which is in one-to-one correspondence with grid points on the migration profile, and each imaging point has a dip angle.

[0060] 4. Determine a dip-angle effective imaging area of a target imaging point according to the true stratigraphic dip-angle field and the initial migration profile, and screen out dip-angle domain common imaging point gathers located in the dip-angle effective area.

[0061] The dip-angle effective imaging area of the target imaging point x0 is represented as follows:

[0062]

[0063] wherein β1 and β2 represent constraint ranges on the left and right sides of the true stratigraphic dip angle, respectively. β1 and β2 are known and can be artificially given by observing the quality of seismic data, and are generally 10 degrees.

[0064] The amplitude value of the dip-angle domain common imaging point gather at the target imaging point x0 in the dip-angle effective imaging area needs to satisfy the following condition:

[0065]

[0066] wherein I(x0) is the amplitude value of the dip-angle domain common imaging point gather at the target imaging point x0 in the initial imaging profile, and c is an adjustable coefficient less than 1, generally 0.1-0.3. At each target imaging point, different angles have different amplitude values, the maximum value of the amplitude absolute value of the dip-angle domain common imaging point gather in the initial imaging profile is first calculated, and then the threshold range is given by c to screen the angles meeting the condition, and thus the dip-angle domain common imaging point gather in the effective imaging region is obtained.

[0067] 5. The dip-angle domain common imaging point gather in the effective imaging region is subjected to superposition imaging to obtain a final migration imaging profile.

[0068] The final migration imaging profile at the target imaging point x0 of the underground target is obtained by using the following formula:

[0069]

[0070] wherein S final (x0) is the final migration imaging profile at the target imaging point x0.

[0071] In order to verify the effectiveness of the migration imaging profile obtained by the dip-angle scanning, the present application performs numerical verification by using a depth domain migration velocity model of a work area, and in the present embodiment, a smoothed Marmousi model is used for verification. As shown in Figure 3 , the grid scale of the smoothed Marmousi model is set to 737*750, and the longitudinal and transverse sampling intervals are set to 4m and 12.5m respectively. Figure 4 It is a single-shot geophone point observation record, the time sampling length is 3s, and the sampling interval is 4ms.

[0072] The Gaussian beam depth migration method is used to extract the original seismic data to obtain the dip-angle domain common imaging point gather, as shown in Figure 5 . The initial migration imaging profile is obtained by superimposing the dip-angle domain common imaging point gather, as shown in Figure 6 and Figure 10 It can be seen from the figures that: 1) most of the events are in the shape of "smile", the stable phase vertex of which indicates the dip angle of the reflection layer structure, and the effective imaging energy thereof is mainly concentrated in a relatively narrow angle range (near the stable phase vertex); 2) the local discontinuities (such as faults, pinchouts and other structures) in the underground medium will produce diffracted waves, the response characteristics of which in the dip-angle domain common imaging point gather are horizontal straight lines or quasi-linear curves, and the angle range is relatively wide. Therefore, the dip-angle range of the effective imaging region can be determined according to the response characteristics of the reflected waves and the diffracted waves. The true stratigraphic dip angle field is calculated by using the dip-angle scanning formula, as shown in Figure 7 . The dip-angle common imaging point gather located in the effective imaging region is determined, as shown in Figure 8The final migration imaging profile is obtained by stacking and imaging the dip angle common imaging point gathers in the dip angle effective imaging area, as shown in FIG. 6. Figure 9 and Figure 11 It can be found by comparison that the migration imaging profile obtained by the dip angle scanning has higher signal-to-noise ratio, and the method of the present application can effectively enhance the signal-to-noise ratio of the Gaussian beam migration imaging profile, so that the migration imaging profile is more accurate and reliable.

Claims

1. A method for generating a migration imaging section based on tilt scanning, characterized in that: The steps include: Extract dip domain common imaging point gathers from original seismic data; Perform stack imaging on all the common imaging point gathers in the dip domain to obtain the initial migration imaging section; Perform dip scanning on the initial migration imaging section to obtain the true formation dip field; According to the true formation dip field and the initial imaging profile, the effective dip imaging area of ​​the target imaging point is determined, and the dip domain common imaging point gathers within the effective dip imaging area are obtained; The dip domain common imaging point gathers within the effective dip imaging area are stacked and imaged to obtain the final migration imaging section.

2. The method for generating a migration imaging section based on tilt scanning according to claim 1, characterized in that: The true formation dip is obtained by using the dip scanning formula, and the true formation dip is arranged in a set order to obtain the true formation dip field. The dip scanning formula is: Where θ is the true formation dip obtained by dip scanning, Δx is the horizontal unit length of the initial migration imaging section, Δz is the vertical unit length of the initial migration imaging section, and win is the time window used for dip scanning.

3. The method for generating a migration imaging section based on tilt scanning according to claim 1, characterized in that: The effective imaging area of ​​the inclination angle at the target imaging point is: Where θ is the true formation dip obtained by dip scanning, is the inclination angle at the target imaging point x0, β1 and β2 represent the constraint range on the left and right sides of the true formation inclination, respectively.

4. The method for generating a migration imaging section based on tilt scanning according to claim 1, characterized in that: Obtain dip domain common imaging point gathers within the dip effective imaging area based on the following filtering conditions: in, is the dip domain common imaging point gather amplitude value at the target imaging point x0 in the dip effective imaging area, I(x0) is the dip domain common imaging point gather amplitude value at the target imaging point x0 in the initial imaging section, and c is an adjustable coefficient less than 1.

5. The method for generating a migration imaging section based on tilt scanning according to claim 1, characterized in that: The calculation formula for stacking imaging of dip domain common imaging point gathers within the dip effective imaging area is: Among them, S final (x0) is the final migration imaging section at the target imaging point x0, is the inclination angle at the target imaging point x0, is the dip domain common imaging point gather amplitude value at the target imaging point x0 within the dip effective imaging area.

6. The method for generating a migration imaging section based on tilt scanning according to claim 1, characterized in that: The method for extracting the dip domain common imaging point gather of the original seismic data is to calculate the dip at the target imaging point based on the original seismic data and the Gaussian beam depth migration method, and then perform prestack depth migration on the dip to obtain the dip domain common imaging point gather of the original seismic data.

7. The method for generating a migration imaging section based on tilt scanning according to claim 6, characterized in that: The calculation formula for the inclination angle at the target imaging point is: in, is the inclination angle at the target imaging point x0, From the gun point x s The beam spreading angle, is from the detector x r beam spreading angle.

8. The method for generating a migration imaging section based on tilt scanning according to claim 7, characterized in that: The calculation formula of the beam propagation angle is: Where angle is the beam propagation angle, p x 、p z are the horizontal and vertical components of the beam ray parameters, π is the pi, and arctan is the inverse tangent calculation function.

Images