A method and device for improving the imaging accuracy of steep dip structures

Abstract

The present disclosure relates to a method for improving the imaging accuracy of steep dip structures, including: preprocessing the acquired CMP gather and depth domain layer velocity model; determining the pseudo-dip gather of the preprocessed CMP gather and determining the initial prestack depth migration profile according to the depth domain layer velocity model; on the pseudo-dip gather corresponding to the selected profile, picking imaging parameters according to the spatial Fresnel zone, and respectively judging whether the formation dip angle corresponding to the imaging parameters at each depth position on the pseudo-dip gather is a dipping structure. If so, adjusting the imaging parameters at that depth position according to a predetermined rule; selecting the CMP gather corresponding to the interpolated and smoothed imaging parameters for prestack depth migration to obtain a prestack depth migration profile in the depth domain. To solve the problem that when imaging the steep dip structure area in the past, due to the inability to meet the requirements of a large enough offset and dense trace interval, the imaging accuracy of the steep dip structure is low and accurate imaging cannot be achieved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of seismic data processing, and particularly to a method and device for improving the imaging accuracy of steep-dip structures. Background Art

[0002] The seismic imaging accuracy in complex structural areas is of great significance for reservoir exploration. Deep structures such as underwater fans are all good targets for reservoir exploration. When designing the seismic acquisition observation system, due to reasons such as acquisition economy, it is often impossible to ensure a large enough offset. According to the classical reflected wave seismic ray theory, a limited offset cannot guarantee the imaging accuracy of steep-dip structures. In addition, without increasing the trace interval during the processing, the improvement of the resolution of steep-dip structures is very likely to cause the appearance of spatial aliasing, which is a normal phenomenon caused by the Nyquist law. However, the cost of increasing the trace interval during the acquisition stage is too high, and it is usually impossible to increase the trace interval due to economic reasons. How to improve the imaging accuracy of steep-dip structures in deep complex structural areas has always been a difficult point in seismic processing technology. Due to the inability to meet the requirements of large offset and increased trace interval, the steep-dip structures cannot be accurately imaged. Summary of the Invention

[0003] The present disclosure proposes a technical solution for a method and device for improving the imaging accuracy of steep-dip structures, so as to solve the problem that when imaging a steep-dip structural area in the past, due to the inability to ensure a large enough offset and the requirement of increasing the trace interval, the imaging accuracy of the steep-dip structure is low and accurate imaging cannot be achieved.

[0004] According to one aspect of the present disclosure, there is provided a method for improving the imaging accuracy of steep-dip structures, including:

[0005] Obtaining a CMP gather of the work area and a depth-domain layer velocity model, and preprocessing the CMP gather and the depth-domain layer velocity model;

[0006] Using a pseudo-dip calculation formula to determine a pseudo-dip gather of the preprocessed CMP gather; determining an initial prestack depth migration profile according to the preprocessed depth-domain layer velocity model, and selecting profiles from the initial prestack depth migration profile at a predetermined interval;

[0007] On the pseudo-dip gather corresponding to the selected profile, picking imaging parameters according to the spatial Fresnel zone, and respectively determining whether the formation dip angle corresponding to the imaging parameters at each depth position on the pseudo-dip gather is a dipping structure. If so, adjusting the imaging parameters at this depth position according to a predetermined rule;

[0008] Interpolate and smooth the imaging parameters over the entire imaging spatial range, and select the CMP gather corresponding to the interpolated and smoothed imaging parameters for prestack depth migration to obtain a prestack depth migration profile in the depth domain;

[0009] Convert the prestack depth migration profile in the depth domain using the vertical conversion method to obtain an offset result profile in the time domain.

[0010] Preferably, the method for preprocessing the CMP gather and the depth-domain layer velocity model includes:

[0011] Perform gather extraction on the CMP gather and retain the predetermined coordinate information;

[0012] Perform gridding and resampling on the CMP gather after gather extraction and the depth-domain layer velocity model respectively, so that the CMP gather and the depth-domain layer velocity model have the same line trace number and sampling interval.

[0013] Preferably, the method for determining the apparent dip gather of the preprocessed CMP gather using the apparent dip calculation formula includes:

[0014] On the preprocessed CMP gather, calculate the apparent dip value corresponding to each gather data using the apparent dip calculation formula respectively to obtain the apparent dip gather.

[0015] Preferably, the apparent dip calculation formula is:

[0016]

[0017] In the formula, tanθ x is the dip gather in the X direction (same as the main survey line direction) in the three-dimensional spatial coordinate system, tanθ y is the dip gather in the Y direction (same as the tie survey line direction) in the three-dimensional spatial coordinate system, z is the vertical depth of the CMP point position, with the unit of m, x and y are the common midpoint coordinates of the CMP gather, x s and y s are the shot point coordinates, x g and y g are the geophone point coordinates, r s , r g are the distances from the shot and geophone points S, G to the imaging point I respectively.

[0018] Preferably, the method for determining the initial prestack depth migration profile based on the preprocessed depth-domain layer velocity model includes:

[0019] Use the wavefront reconstruction method to determine the travel time information at each geophone point of the depth-domain layer velocity model;

[0020] According to the travel time information, prestack depth migration is performed on the preprocessed CMP gather by using integral migration to generate an initial prestack depth migration profile.

[0021] Preferably, the interpolation process is Lagrange interpolation.

[0022] Preferably, on the pseudo-dip gather corresponding to the selected profile, the method for picking imaging parameters according to the spatial Fresnel zone includes:

[0023] Taking the dip value of 0 degrees on the pseudo-dip gather as the center point, and picking the dip values within the range with the spatial Fresnel zone as the width as imaging parameters.

[0024] Preferably, the predetermined rule is:

[0025] If it is determined that the inclined structure is a positive dip structure, then move the center point of the imaging parameters at the depth position of the positive dip structure horizontally in the positive direction of the dip value to a predetermined position;

[0026] If it is determined that the inclined structure is a negative dip structure, then move the center point of the imaging parameters at the depth position of the negative dip structure horizontally in the negative direction of the dip value to a predetermined position;

[0027] Expand the width of the imaging parameters at the depth position of the inclined structure by a predetermined number of times.

[0028] Preferably, the predetermined position is:

[0029] The dip value on the pseudo-dip gather corresponding to the center point is the formation dip value at the same depth position on the initial prestack depth migration profile corresponding to the depth position of the center point on the pseudo-dip gather where the center point is located.

[0030] According to one aspect of the present disclosure, there is provided an apparatus for improving the imaging accuracy of steep dip structures, characterized by comprising:

[0031] An acquisition unit for acquiring a CMP gather of a work area and a depth-domain layer velocity model, and preprocessing the CMP gather and the depth-domain layer velocity model;

[0032] A pseudo-dip gather determination unit for determining the pseudo-dip gather of the preprocessed CMP gather by using a pseudo-dip calculation formula;

[0033] An initial prestack depth migration profile generation unit for determining an initial prestack depth migration profile according to the preprocessed depth-domain layer velocity model, and selecting profiles from the initial prestack depth migration profile at a predetermined interval;

[0034] An imaging parameter picking unit, which is used to pick imaging parameters according to the spatial Fresnel zone on the pseudo-dip angle gather corresponding to the selected profile, and respectively determine whether the formation dip angle corresponding to the imaging parameter at each depth position on the pseudo-dip angle gather is a dipping structure. If so, adjust the imaging parameter at this depth position according to a predetermined rule;

[0035] A pre-stack depth migration profile generation unit in the depth domain, which is used to perform interpolation processing and smoothing processing on the imaging parameters within the full imaging spatial range, select the CMP gather corresponding to the interpolated and smoothed imaging parameters for pre-stack depth migration, and obtain a pre-stack depth migration profile in the depth domain;

[0036] A time-domain migration result profile generation unit, which is used to convert the pre-stack depth migration profile in the depth domain by using the vertical conversion method to obtain a time-domain migration result profile.

[0037] The present invention has at least the following beneficial effects:

[0038] A method and device for improving the imaging accuracy of steep dip structures proposed in the present disclosure, by obtaining a pseudo-dip angle gather from the CMP gather, and determining its initial pre-stack depth migration profile from the depth-domain layer velocity model, picking imaging parameters on the pseudo-dip angle gather corresponding to the initial pre-stack depth migration profile, and using them to subsequently select the corresponding CMP gather for pre-stack depth migration profile imaging in the depth domain, to obtain a migration result profile with enhanced imaging of steep dip structures. This method does not require in-line interpolation of pre-stack seismic data or pre-stack data regularization processing. While enhancing the imaging of steep dip structures, it prevents the occurrence of spatial aliasing phenomena. Description of the Drawings

[0039] The drawings here are incorporated into the specification and form a part of this specification. These drawings show embodiments consistent with the present disclosure and are used together with the specification to illustrate the technical solutions of the present disclosure.

[0040] Figure 1 Shows a flowchart of a method for improving the imaging accuracy of steep dip structures according to an embodiment of the present disclosure.

[0041] Figure 2 Shows the imaging parameters picked on the pseudo-dip angle gather corresponding to the profile selected at a predetermined interval by the method of the present invention according to an embodiment of the present disclosure.

[0042] Figure 3 Shows the imaging parameters picked on the pseudo-dip angle gather corresponding to the profile selected at a predetermined interval by the traditional migration aperture according to an embodiment of the present disclosure.

[0043] Figure 4 Shows according to an embodiment of the present disclosure using Figure 2The time-domain migration result profile obtained from the picked imaging parameters.

[0044] Figure 5 Shows the use of Figure 3 The time-domain migration result profile obtained from the picked imaging parameters. Detailed implementation manners

[0045] 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 drawings denote elements having the same or similar functions. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0046] The term "exemplary" used herein means "serving as an example, embodiment, or illustration". Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or better than other embodiments.

[0047] The term "and / or" herein is merely a description of an association relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the term "at least one" herein means any one of a plurality or any combination of at least two of a plurality. For example, including at least one of A, B, and C can represent any one or more elements selected from the set composed of A, B, and C.

[0048] In addition, for a better description of the present disclosure, numerous specific details are given in the following detailed implementation manners. Those skilled in the art should understand that the present disclosure can also be implemented without some specific details. In some instances, methods, means, elements, and circuits well-known to those skilled in the art are not described in detail so as to highlight the gist of the present disclosure.

[0049] It can be understood that the above-mentioned various method embodiments of 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 elaborate further.

[0050] Figure 1 A flowchart showing a method for improving the imaging accuracy of steep-dip structures according to an embodiment of the present disclosure. Figure 2 Shows the imaging parameters picked on the virtual dip angle gather corresponding to the profiles selected at a predetermined interval by the method of the present invention according to an embodiment of the present disclosure. Figure 3 Shows the imaging parameters picked on the virtual dip angle gather corresponding to the profiles selected at a predetermined interval by the traditional migration aperture according to an embodiment of the present disclosure. Figure 4 Shows the use of Figure 2The time-domain migration result profile obtained from the picked imaging parameters. Figure 5 It shows that in accordance with an embodiment of the present disclosure, by using Figure 3 the picked imaging parameters, the time-domain migration result profile is obtained. As Figure 1 , 2 , 3, 4, and 5 show, the method for improving the imaging accuracy of steep-dip structures includes: Step S101: Obtain the CMP gather of the work area and the depth-domain layer velocity model, and preprocess the CMP gather and the depth-domain layer velocity model; Step S102: Use the pseudo-dip angle calculation formula to determine the pseudo-dip angle gather of the preprocessed CMP gather; According to the preprocessed depth-domain layer velocity model, determine the initial prestack depth migration profile, and select profiles from the initial prestack depth migration profile at a predetermined interval; Step S103: On the pseudo-dip angle gather corresponding to the selected profile, pick the imaging parameters according to the spatial Fresnel zone, and respectively determine whether the formation dip angle corresponding to the imaging parameters at each depth position on the pseudo-dip angle gather is a dipping structure. If so, adjust the imaging parameters at this depth position according to a predetermined rule; Step S104: Perform interpolation processing and smoothing processing on the imaging parameters within the full imaging spatial range, select the CMP gather corresponding to the interpolated and smoothed imaging parameters for prestack depth migration, and obtain the depth-domain prestack depth migration profile; Step S105: Convert the depth-domain prestack depth migration profile by using the vertical conversion method to obtain the time-domain migration result profile. This is to solve the problem that when imaging a steep-dip structure area in the past, due to the inability to ensure the requirements of a large enough offset and a dense trace interval, the imaging accuracy of the steep-dip structure is low and accurate imaging cannot be achieved.

[0051] The embodiment of the present invention provides a method for improving the imaging accuracy of steep-dip structures, which specifically includes the following steps:

[0052] Step S101: Obtain the CMP gather of the work area and the depth-domain layer velocity model, and preprocess the CMP gather and the depth-domain layer velocity model.

[0053] In the present disclosure, the method for preprocessing the CMP gather and the depth-domain layer velocity model includes: performing trace gather processing on the CMP gather and retaining the predetermined coordinate information; respectively performing grid processing and resampling processing on the CMP gather after the trace gather processing and the depth-domain layer velocity model, so that the CMP gather and the depth-domain layer velocity model have the same line trace number and sampling interval.

[0054] In the embodiments of the present disclosure, before preprocessing the CMP gather and the depth-domain layer velocity model, static correction, noise suppression, amplitude compensation, deconvolution, residual static correction, and anti-geometric spreading compensation processing are respectively performed on the obtained CMP gather and the depth-domain layer velocity model to facilitate subsequent operations.

[0055] For the CMP gather data after the above processing, gather extraction is performed. Gather extraction is a process of first extracting the stacked traces of each common reflection point and arranging them according to the shot interval size for the convenience of stacking and calculating the velocity spectrum. During the gather extraction process, predetermined coordinate information is to be retained for subsequent calculation of the quasi-dip gather. Among them, the predetermined coordinate information includes: 1. The common midpoint coordinates x and y, 2. The shot point coordinates x s and y s , and 3. The geophone point coordinates x g and y g , and the above three groups of coordinates are retained.

[0056] The CMP gather and the depth-domain layer velocity model after gather extraction are subjected to grid processing so that the physical points with the same geodetic coordinates of the two have the same line trace numbers; the CMP gather and the depth-domain layer velocity model after gather extraction are subjected to resampling processing so that the CMP gather and the depth-domain layer velocity model have the same sampling interval; after completing the above preprocessing work, it can be ensured that the depth-domain layer velocity model and the pre-stack CMP gather are exactly the same in the spatial range.

[0057] Step S102: Use the quasi-dip calculation formula to determine the quasi-dip gather of the preprocessed CMP gather; determine the initial pre-stack depth migration profile according to the preprocessed depth-domain layer velocity model, and perform profile selection on the initial pre-stack depth migration profile at a predetermined interval.

[0058] In the present disclosure, the method for using the quasi-dip calculation formula to determine the quasi-dip gather of the preprocessed CMP gather includes: on the preprocessed CMP gather, using the quasi-dip calculation formula to calculate the quasi-dip value corresponding to each gather data respectively to obtain the quasi-dip gather.

[0059] In the present disclosure, the quasi-dip calculation formula is:

[0060]

[0061] In the formula, tanθ x is the dip gather in the X direction (the same as the main survey line direction) in the three-dimensional space coordinate system, tanθ y is the dip gather in the Y direction (the same as the connecting survey line direction) in the three-dimensional space coordinate system, z is the vertical depth of the CMP point position, the unit is m, x and y are the common midpoint coordinates of the CMP gather, x sand s is the shot point coordinate, x g and g are the coordinates of the detection point.

[0062] In the embodiment of the present disclosure, the pseudo-inclination calculation formula is simplified from the depth domain inclination calculation formula, wherein the depth domain inclination calculation formula is:

[0063]

[0064] Where z is the vertical depth of the current CMP point in meters, x and y are the coordinates of the common center point of the CMP gather, and E s , E g are the slowness from the shot check point S, G to the imaging point I, t s ,t g are the travel time from the inspection points S and G to the imaging point I; r s ,r g are the distances from the inspection points S and G to the imaging point I respectively.

[0065] Assuming that the first-order derivative of the slowness is zero, the depth domain dip in equation (2) can be simplified to a pseudo-dip gather, that is, equation (1). The calculation of generating the pseudo-dip gather does not require differentiation, and the calculation efficiency is very high, that is:

[0066]

[0067] In pre-stack depth migration, the travel time table is obtained by ray tracing. When there is a lateral difference in the velocity body, the ray bends and the corresponding ray angle also changes. The dip angle here is the dip angle of the plane determined by the normal angle between the instantaneous incident ray and the instantaneous reflected ray. The calculation of this dip angle requires constructing the travel time gradient direction based on the travel time of the surrounding points at the imaging point. This travel time gradient direction is the ray direction, and then the reflection surface angle is calculated. The dip angle obtained by this method has a large fluctuation and requires a high degree of smoothness of the travel time table. A slightly non-smooth travel time surface will lead to the splitting of the ray angle, that is, the adjacent angles are very different. This is very unfavorable for the dip gather used to divide the Fresnel zone and the non-Fresnel zone, because it will make the dip angles obtained at the original continuous positions very different, which is not conducive to the picking and screening of the Fresnel zone.

[0068] Therefore, we adopt the dip relationship constructed by more direct simple geometric relationships instead of the instantaneous dip. That is to say, when calculating the incident ray and the reflected ray, we no longer use the gradient direction of the isochronal surface, but directly utilize the simple triangle formed by the shot imaging point and the receiver imaging point, and then use the same solution formula as time migration to obtain the dip of the imaging position, which is called the pseudo-dip gather in the present invention. This simplification is sufficient for picking up the data involved in the calculation on the dip gather, because the purpose of the pseudo-dip gather is to distinguish the Fresnel zones that contribute to imaging from the signals that do not contribute to imaging. Using a simple dip will cause a certain degree of distortion in the generated depth-domain dip gather, but it will not affect its essential relationship, and there is no ray angle splitting in this simple geometric relationship dip, which increases the robustness of the dip gather technology.

[0069] When calculating the pseudo-dip gather, substitute the gather data of each CMP point into the above-mentioned pseudo-dip calculation formula respectively, calculate the pseudo-dip value corresponding to each gather data, and all the pseudo-dip values form the pseudo-dip gather.

[0070] In the present disclosure, the method for determining the initial prestack depth migration profile according to the preprocessed depth-domain layer velocity model includes: using the wavefront reconstruction method to determine the travel time information at each receiver point of the depth-domain layer velocity model; according to the travel time information, using the integral migration method to perform prestack depth migration on the preprocessed CMP gather to generate the initial prestack depth migration profile.

[0071] In the embodiment of the present disclosure, before determining the initial prestack depth migration profile according to the preprocessed depth-domain layer velocity model, it further includes: performing a smoothing process on the depth-domain layer velocity model. Among them, the smoothing process can be moving average, or triangular average, or Gaussian filtering, or damped least squares smoothing process.

[0072] The smoothing process is to eliminate the singular points in the velocity model during ray tracing. The smoothing process is not only important for the ray tracing process, but also affects the migration imaging effect. The meaning of smoothing includes the following three points: 1. Ensure the applicability of ray tracing; 2. Increase the calculation speed of ray tracing; 3. Reduce the memory requirement of the input quantity. Smoothing is a process that occurs naturally during seismic wave propagation. In fact, the effective velocity of actual wave propagation may be some average values within the first Fresnel zone. If the depth-domain layer velocity model is known and the velocity field of the model is smooth enough, the ray trajectory can be directly calculated. In practice, the velocities of each layer are given in numerical form, and it is difficult to ensure that its velocity and interface are smooth enough. At this time, it is necessary to perform a smoothing process on the velocity.

[0073] For the smoothed depth-domain layer velocity model, traveltime information at each geophone point is calculated through the wavefront reconstruction method. Using the calculated traveltime information, the Kirchhoff integral migration method is employed to perform initial prestack depth migration on the preprocessed CMP gather, enabling the stacking of common reflection points and the migration of diffracted points in the CMP gather to restore their original true positions. After completing the initial prestack depth migration process, an initial prestack depth migration profile is generated for reference during comparison and the selection of subsequent imaging parameters.

[0074] After generating the initial prestack depth migration profile, some of these profiles need to be selected at a predetermined interval for subsequent operations. Selecting profiles at a predetermined interval is to make the data volume of the selected pseudo-dip gathers smaller when selecting the corresponding pseudo-dip gathers based on the initial prestack depth migration profile subsequently, thereby saving time for picking imaging parameters in the follow-up. For example, the value of the predetermined interval can be 100, that is, on the initial prestack depth migration profile, one profile is selected every 100 profiles. In practical applications, the number of the predetermined interval can be adjusted according to the size of the entire migrated profile data volume.

[0075] Step S103: On the pseudo-dip gather corresponding to the selected profile, pick imaging parameters according to the spatial Fresnel zone, and respectively determine whether the formation dip angle corresponding to the imaging parameter at each depth position on the pseudo-dip gather is an inclined structure. If so, adjust the imaging parameter at this depth position according to a predetermined rule.

[0076] In the present disclosure, the method of picking imaging parameters according to the spatial Fresnel zone on the pseudo-dip gather corresponding to the selected profile includes: taking the dip angle value of 0 degrees on the pseudo-dip gather as the center point, and picking the dip angle values within the range with the spatial Fresnel zone as the width as imaging parameters.

[0077] In the present disclosure, the predetermined rule is: judge that if the inclined structure is a positive dip angle structure, then horizontally move the center point of the imaging parameter at the depth position of the positive dip angle structure to a predetermined position in the positive direction of the dip angle value; judge that if the inclined structure is a negative dip angle structure, then horizontally move the center point of the imaging parameter at the depth position of the negative dip angle structure to a predetermined position in the negative direction of the dip angle value; expand the width of the imaging parameter at the depth position of the inclined structure by a predetermined number of times.

[0078] In the present disclosure, the predetermined position is: the dip angle value on the pseudo-dip gather corresponding to the center point, which is the formation dip angle value at the same depth position on the initial prestack depth migration profile corresponding to the depth position of the center point in the pseudo-dip gather where the center point is located.

[0079] In the embodiments of the present disclosure, after selecting profiles at a predetermined interval on the initial pre-stack depth migration section, the corresponding pseudo-dip gathers of these profiles are retrieved, and imaging parameters need to be picked up on the pseudo-dip gathers corresponding to the selected profiles.

[0080] The pseudo-dip gathers corresponding to the profiles selected at a predetermined interval on the initial pre-stack depth migration section are as Figure 2 shown. On Figure 2 , the vertical coordinate is the depth position, and the horizontal coordinate is the dip value. As can be seen from Figure 2 , in the depth-dip domain, the gather corresponding to the flat-layer reflection event is arc-shaped, and the center position of the arc is near the dip value of 0 degrees. The midpoint of the arc corresponding to the steep-dip event is far from the center line where dip (formation dip) is 0 degrees. Different dip seismic reflection information corresponding to different depths can be distinguished on the pseudo-dip gathers in the depth-dip domain.

[0081] To pick up the imaging parameters, first, the center point is the dip value of 0 degrees on the pseudo-dip gather, and the imaging parameters are picked up with the spatial Fresnel zone as the width. As Figure 2 shown, the imaging parameters picked up at the depth position of 0 - 2 km on Figure 2 are the data within the reserved calculation area inside the white line.

[0082] During seismic wave migration imaging, the response and information in a region adjacent to the incident and outgoing ray paths related to a certain imaging point contribute (affect) the most to this imaging point during the migration process. This region is called the spatial Fresnel zone. It can be seen from the pseudo-dip gather that the formation dip in the shallow layer region of 0 - 2 km here is a gentle region, and the horizontal formation diffractions in the gentle region are relatively concentrated. The imaging parameters favorable for subsequent steep-dip imaging are concentrated within the width range of the spatial Fresnel zone near the center point where the pseudo-dip value is zero degrees. Picking up the seismic data within the spatial Fresnel zone area for calculation can significantly improve the signal-to-noise ratio of the migration results.

[0083] On the pseudo-dip gather, as the depth increases, obvious inclined structures begin to exist on the section. If the inclined structure is a positive dip structure, that is, the position of the inclined structure is in the positive dip value direction on the pseudo-dip gather, then the center point with the original dip value of 0 degrees of the imaging parameters at the depth position where the positive dip structure appears needs to be horizontally moved in the positive dip direction; if the inclined structure is a negative dip structure, that is, the position of the inclined structure is in the negative dip value direction on the pseudo-dip gather, then the center point with the original dip value of 0 degrees of the imaging parameters at the depth position where the negative dip structure appears needs to be horizontally moved in the negative dip direction.

[0084] Taking Figure 2Taking the medium depth position of 5.5 km as an example, if the formation dip angle at this depth position is an inclined structure and a negative dip angle structure, then the center point of the imaging parameters at the 5.5 km depth position needs to be horizontally moved in the direction of the negative dip angle, that is, in the direction where the dip angle value is negative, until the dip angle value corresponding to the center point is equal to the formation dip angle value at the same depth position on the initial prestack depth migration section, that is, at the 5.5 km depth position. If the formation dip angle value at the 5.5 km depth position on the initial prestack depth migration section is -5 degrees, then the center point of the imaging parameters at the 5.5 km depth position on the pseudo-dip angle gather needs to be horizontally moved in the direction of the negative dip angle to the position where the corresponding dip angle value is -5 degrees. The position of the center point of the imaging parameters cannot exceed the formation dip angle value on the migration section, otherwise imaging artifacts will be generated and the channel ratio of the migration result will be reduced.

[0085] After the center point moves, the spatial Fresnel zone width region originally symmetric on both sides of the center point also moves horizontally in the direction of the negative dip angle as a whole. That is to say, after the dip angle value of the center point moves -5 degrees, the minimum dip angle value and the maximum dip angle value in the picked imaging parameters at the 5.5 km depth position both move -5 degrees at the same time.

[0086] After moving the center point of the imaging parameters at the depth position of the inclined structure on the pseudo-dip angle gather to the predetermined position according to the predetermined rule, the width of the imaging parameters at the depth position of the inclined structure on all pseudo-dip angle gathers is expanded to a predetermined number of times the original, where the predetermined number is: 1.5. That is to say, after the center point, the minimum dip angle value, and the maximum dip angle value of the imaging parameters at the 5.5 km depth position move -5 degrees in the direction of the negative dip angle from the original position, while keeping the center point at the predetermined position unchanged, the minimum dip angle value continues to move in the direction of the negative dip angle value, and at the same time the maximum dip angle value moves in the direction of the positive dip angle value until the width between the minimum dip angle value and the maximum dip angle value is expanded to 1.5 times the original spatial Fresnel zone width. The reason for expanding the width of the imaging parameters to 1.5 times the original is that the diffraction divergence of the inclined formation is not focused, and after expansion, the parameters beneficial to the subsequent screening of the CMP gather can be picked up on the pseudo-dip angle gather. If the width of the imaging parameters at the depth position of the inclined structure is expanded by more than 1.5 times, excessive migration noise will be introduced, affecting the channel ratio of the migration result; less than 1.5 times will cause the steep dip angle structure not to be imaged.

[0087] In the embodiment of the present disclosure, Figure 2 The reserved calculation area circled by the white line in is the imaging parameters picked on the pseudo-dip angle gather corresponding to the section after selecting the section at a predetermined interval according to the above steps; Figure 3 are the imaging parameters picked according to the traditional migration aperture of the existing commercial seismic processing software. Figure 2 and Figure 3By comparison, it can be seen that the imaging parameters picked up by the method of the present disclosure are more accurate, and a lot of data that would affect the migration results is removed.

[0088] Step S104: Perform interpolation processing and smoothing processing on the imaging parameters within the full imaging spatial range, and select the CMP gather corresponding to the interpolated and smoothed imaging parameters for prestack depth migration to obtain a prestack depth migration profile in the depth domain.

[0089] In the present disclosure, the interpolation processing is Lagrange interpolation processing.

[0090] In the embodiment of the present disclosure, after the imaging parameters are picked up, since the picked imaging parameters are picked up based on the pseudo-dip gathers corresponding to the sections selected at a predetermined interval, rather than the pseudo-dip gathers obtained in the complete step S102, it is necessary to perform interpolation processing on the picked imaging parameters in the full spatial range to make them correspond to the CMP gathers, that is, each CMP gather has corresponding interpolated imaging parameters.

[0091] Among them, Lagrange interpolation processing is selected for the interpolation processing. Lagrange interpolation processing has strong applicability. It can perform good spatial interpolation on spatially irregular imaging parameters. For spatially regular imaging parameters, it can be directly simplified to linear interpolation to avoid sudden changes in the interpolation results. Among them, the Lagrange interpolation formula specifically includes:

[0092] Among any given set of 2n + 2 numbers x1, x2,..., xn+1, y1, y2,..., yn+1, where x1, x2,... xn+1 are all different, there exists a unique polynomial pn(x) with a degree not exceeding n that satisfies pn(xi) = yi (i = 1, 2,..., n + 1), and there is:

[0093]

[0094] In the formula: p(x) is the interpolated function, n is the maximum number, x is the x coordinate of a certain point in the function (or polynomial), y is the value (y coordinate) of a certain point in the function (or polynomial), i and j are numbers (positive integers not equal to 0), x i is the x coordinate of the i-th point, x j is the x coordinate of the j-th point.

[0095] Formula (3) is the value after Lagrange algorithm interpolation. If the processing grid of seismic data is regular and there is data in each grid, Lagrange interpolation can be simplified to linear interpolation, and the formula is:

[0096]

[0097] Where: y is the output value after interpolation at a certain point in the function, x is the x - coordinate of a certain point in the function, x1 is the x - coordinate of point 1 in the function, x2 is the x - coordinate of point 2 in the function, y1 is the value of point 1 in the function (or the y - coordinate of point 1), and y2 is the value of point 2 in the function (or the y - coordinate of point 2).

[0098] Smoothing the imaging parameters after interpolation processing for the entire imaging space range, avoiding or eliminating calculation errors caused by too rapid lateral changes in velocity, reducing errors, and improving the accuracy of migration imaging.

[0099] Select the CMP gather corresponding to the imaging parameters after the interpolation and smoothing processing: Each imaging parameter has its corresponding CMP gather. Cut off the CMP gathers outside the imaging parameter in the CMP gather corresponding to each imaging parameter, and retain the CMP gathers inside the imaging parameter to participate in the subsequent prestack depth migration processing. After the prestack depth migration processing of the CMP gathers inside the imaging parameter, a prestack depth migration profile in the depth domain can be obtained.

[0100] Step S105: Convert the prestack depth migration profile in the depth domain using the vertical conversion method to obtain an offset result profile in the time domain.

[0101] In the embodiment of the present disclosure, according to the prestack depth migration profile obtained in step S104, using the vertical conversion method, that is, the principle of depth = velocity × time, an offset result profile in the time domain after conversion from the depth domain is obtained, which is used for subsequent seismic data interpretation in the time domain and seismic reservoir prediction work.

[0102] Figure 2 For the imaging parameters picked on the pseudo - dip gathers corresponding to the profiles selected at a predetermined interval by the method of the present invention, according to Figure 2 the prestack depth migration of the corresponding CMP gathers is performed based on the picked imaging parameters, and the obtained prestack depth migration profile in the depth domain is converted into an offset result profile in the time domain, and the result is as Figure 4 shown; Figure 3 For the imaging parameters picked on the pseudo - dip gathers corresponding to the profiles selected at a predetermined interval by the traditional migration aperture, according to Figure 3 the prestack depth migration of the corresponding CMP gathers is performed based on the picked imaging parameters, and a prestack depth migration profile in the depth domain is obtained, which is converted into an offset result profile in the time domain as Figure 5 shown. From Figure 5 it can be seen that at the position of the steep - dip structure with the horizontal axis coordinate CDP2061 - 2181 and the vertical axis coordinate time 2600ms - 3300ms, the imaging quality of the steep - dip structure is poor, the event is discontinuous, and spatial aliasing also appears; while from Figure 4As can be seen, at the position of the horizontal axis coordinate CDP2061 - 2181 and the vertical axis coordinate time 2600ms - 3300ms, the imaging quality of the steep dip structure is significantly improved. The in-phase axis of the high-steep structure is continuously and significantly enhanced, and no spatial aliasing appears while the steep dip structure is strengthened.

[0103] Based on the wavefield theory, we found that within a limited offset range, the reflection information of the steep dip structure can also be received by surface geophones. When the CMP prestack gather in the x - t domain is processed through a series of calculations to obtain the dip gather, and then the pseudo - dip gather is obtained through approximation and simplification, the reflection information of the steep dip structure can be visually identified on the pseudo - dip gather. Based on the above understanding, the present invention studies a method to improve the imaging accuracy of the steep dip structure. By performing damped least - squares smoothing on the depth - domain layer velocity model, calculating and generating the pseudo - dip gather and picking up the imaging parameters, and performing Lagrangian interpolation on the imaging parameters, the purpose of these processes is to distinguish the data in advance before migration, allowing the data beneficial to the imaging of the steep dip structure to participate in the migration calculation, and screening out the data that is not helpful for the imaging of the steep dip structure and will reduce the signal - to - noise ratio of the results in advance. Its core concept is to identify the reflection characteristics of the steep dip structure on the pseudo - dip gather, strengthen this part of the information during the migration process, and suppress other scattering information that does not promote or has an adverse effect on the imaging of the steep dip structure, so as to obtain the processing result with enhanced imaging of the steep dip structure. The present invention intervenes and optimizes the prestack depth migration result for the first time from the dimension of the pseudo - dip domain, no longer requires interpolation processing to reduce the trace interval of the prestack seismic data, and no spatial aliasing will occur in the migration result of the steep dip structure.

[0104] The execution subject of a method for improving the imaging accuracy of the steep dip structure can be any processing device. For example, the method for improving the imaging accuracy of the steep dip structure can be executed by a terminal device, a server, or other processing devices. Among them, the terminal device can 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 implementation manners, the method for improving the imaging accuracy of the steep dip structure can be implemented by a processor calling computer - readable instructions stored in a memory.

[0105] Those skilled in the art can understand that in the above - mentioned method of the specific implementation manner, the writing order of each step does not mean a strict execution order and does not constitute any limitation to the implementation process. The specific execution order of each step should be determined by its function and possible internal logic.

[0106] The present disclosure also provides a device for improving the imaging accuracy of steep dip structures, including: an acquisition unit configured to acquire a CMP gather of a work area and a depth-domain layer velocity model, and preprocess the CMP gather and the depth-domain layer velocity model; a pseudo-dip gather determination unit configured to determine a pseudo-dip gather of the preprocessed CMP gather by using a pseudo-dip calculation formula; an initial pre-stack depth migration profile generation unit configured to determine an initial pre-stack depth migration profile according to the preprocessed depth-domain layer velocity model, and select profiles from the initial pre-stack depth migration profile at a predetermined interval; an imaging parameter picking unit configured to pick imaging parameters on the pseudo-dip gather corresponding to the selected profile, and respectively determine whether the formation dip angle corresponding to the imaging parameters at each depth position on the pseudo-dip gather is a dipping structure. If so, adjust the imaging parameters at this depth position according to a predetermined rule; a depth-domain pre-stack depth migration profile generation unit configured to perform interpolation processing and smoothing processing on the imaging parameters in the entire imaging space range, select the CMP gather corresponding to the interpolated and smoothed imaging parameters for pre-stack depth migration, and obtain a depth-domain pre-stack depth migration profile; a time-domain migration result profile generation unit configured to convert the depth-domain pre-stack depth migration profile by using a vertical conversion method to obtain a time-domain migration result profile. For specific details, reference may be made to the detailed description in a method for improving the imaging accuracy of steep dip structures.

[0107] In some embodiments, the functions or modules / units included in the device provided by the embodiments of the present disclosure can be used to execute the methods described in the above method embodiments. The specific implementation can refer to the description of the above method embodiments. For the sake of brevity, it will not be repeated here.

[0108] The above has described the embodiments of the present disclosure. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, the practical application, or the technical improvement of the technology in the market, or to enable other ordinary skill in the art in the technical field to understand the disclosed embodiments.

Claims

1. A method for improving the imaging accuracy of steep dip structures, characterized in that, Including: Obtain the CMP gather of the work area and the depth-domain layer velocity model, and preprocess the CMP gather and the depth-domain layer velocity model; Perform smoothing processing on the depth-domain layer velocity model; wherein, the smoothing processing can be moving average, or triangular average, or Gaussian filtering, or damped least squares smoothing processing; Use the pseudo-dip angle calculation formula to determine the pseudo-dip angle gather of the preprocessed CMP gather; according to the preprocessed depth-domain layer velocity model, determine the initial prestack depth migration profile, and select profiles from the initial prestack depth migration profile at a predetermined interval; The method for determining the initial prestack depth migration profile according to the preprocessed depth-domain layer velocity model includes: using the wavefront reconstruction method to determine the travel time information at each geophone point of the depth-domain layer velocity model; according to the travel time information, use the integral migration method to perform prestack depth migration on the preprocessed CMP gather to generate an initial prestack depth migration profile; On the pseudo-dip angle gather corresponding to the selected profile, pick the imaging parameters according to the spatial Fresnel zone, and respectively judge whether the formation dip angle corresponding to the imaging parameters at each depth position on the pseudo-dip angle gather is a dipping structure. If so, adjust the imaging parameters at this depth position according to a predetermined rule; the predetermined rule is: judge that if the dipping structure is a positive dip angle structure, then move the center point of the imaging parameters at the depth position of the positive dip angle structure horizontally to a predetermined position in the direction of the positive dip angle value; judge that if the dipping structure is a negative dip angle structure, then move the center point of the imaging parameters at the depth position of the negative dip angle structure horizontally to a predetermined position in the direction of the negative dip angle value; expand the width of the imaging parameters at the depth position of the dipping structure by a predetermined number of times; the position of the center point of the imaging parameters cannot exceed the formation dip angle value on the migration profile; the dip angle value corresponding to the center point is equal to the formation dip angle value at the same depth position on the initial prestack depth migration profile; wherein, the predetermined number is: 1.5; Perform interpolation processing and smoothing processing on the imaging parameters in the full imaging spatial range, select the CMP gather corresponding to the interpolated and smoothed imaging parameters for prestack depth migration to obtain a depth-domain prestack depth migration profile; the interpolation processing is Lagrange interpolation processing; Convert the depth-domain prestack depth migration profile using the vertical conversion method to obtain a time-domain migration result profile.

2. The method for improving the imaging accuracy of steep dip structures according to claim 1, characterized in that, The method for preprocessing the CMP gather and the depth-domain layer velocity model includes: Perform gather extraction processing on the CMP gather and retain predetermined coordinate information; Perform grid processing and resampling processing on the CMP gather after gather extraction processing and the depth-domain layer velocity model respectively, so that the CMP gather and the depth-domain layer velocity model have the same line trace number and sampling interval.

3. The method for improving the imaging accuracy of steep dip structures according to claim 1 or 2, characterized in that The method for using the pseudo-dip angle calculation formula to determine the pseudo-dip angle gather of the preprocessed CMP gather includes: On the preprocessed CMP gather, use the pseudo-dip angle calculation formula to calculate the pseudo-dip angle value corresponding to each gather data respectively to obtain a pseudo-dip angle gather.

4. The method for improving the imaging accuracy of steep dip structures according to claim 1, characterized in that The formula for the pseudo-dip angle is as follows: where, tanθ x is the dip gather in the X direction (same as the main survey line direction) in the three-dimensional space coordinate system, and tanθ y is the dip gather in the Y direction (same as the connecting survey line direction) in the three-dimensional space coordinate system, z is the vertical depth of the CMP point position, with the unit of m, x and y are the common midpoint coordinates of the CMP gather, x s and y s are the shot point coordinates, x g and y g are the geophone point coordinates, r s , r g are the distances from the shot and geophone points S and G to the imaging point I, respectively.

5. The method for improving the imaging accuracy of steep dip structures according to any one of claims 1-4, characterized in that On the pseudo-dip angle gather corresponding to the selected profile, the method for picking imaging parameters according to the spatial Fresnel zone includes: Taking the dip angle value of 0 degrees on the pseudo-dip angle gather as the center point, pick the dip angle values within the range with the spatial Fresnel zone as the width as the imaging parameters.

6. The method for improving the imaging accuracy of steep dip structures according to claim 1, characterized in that The predetermined position is: The dip angle value on the pseudo-dip angle gather corresponding to this center point is the dip angle value of the formation at the same depth position on the initial pre-stack depth migration profile corresponding to the depth position of the center point on the pseudo-dip angle gather where the center point is located.

7. An apparatus for improving the imaging accuracy of steeply inclined structures, characterized in that, It includes: An acquisition unit for acquiring the CMP gather of the work area and the layer velocity model in the depth domain, and preprocessing the CMP gather and the layer velocity model in the depth domain; A pseudo-dip angle gather determination unit for determining the pseudo-dip angle gather of the preprocessed CMP gather by using the pseudo-dip angle calculation formula; An initial pre-stack depth migration profile generation unit for determining the initial pre-stack depth migration profile according to the preprocessed layer velocity model in the depth domain, and selecting profiles from the initial pre-stack depth migration profile at a predetermined interval; An imaging parameter picking unit for picking imaging parameters according to the spatial Fresnel zone on the pseudo-dip angle gather corresponding to the selected profile, and respectively judging whether the formation dip angle corresponding to the imaging parameter at each depth position on the pseudo-dip angle gather is a tilted structure. If so, adjust the imaging parameter at this depth position according to a predetermined rule; A depth-domain pre-stack depth migration profile generation unit for performing interpolation processing and smoothing processing on the imaging parameters in the entire imaging space range, and selecting the CMP gather corresponding to the interpolated and smoothed imaging parameters for pre-stack depth migration to obtain the depth-domain pre-stack depth migration profile; A time-domain migration result profile generation unit for converting the depth-domain pre-stack depth migration profile by using the vertical conversion method to obtain the time-domain migration result profile.

Images