A method for elastic wave reverse time migration imaging guided by stratigraphic dip for wavefield separation
By using a wavefield separation method guided by stratigraphic dip, the problem of insufficient imaging of Dp-RTM in complex geological structures was solved, and high-resolution elastic wave reverse time migration imaging in complex media was achieved, improving the imaging quality of steeply dipping structures and subsalt boundaries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHENGDU UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2026-03-12
- Publication Date
- 2026-06-02
AI Technical Summary
Existing Dp-RTM methods struggle to simultaneously suppress low-frequency noise and velocity gradient artifacts in complex geological structures, resulting in insufficient illumination of steeply tilted flanks and subsalt boundaries, severe component leakage and residual artifacts, making it difficult to maintain high-resolution imaging in complex geological structures.
A wavefield separation method guided by stratigraphic dip is adopted. By acquiring the initial velocity model and wavefield data of the geological region, multi-directional wavefield decomposition is performed using Hilbert transform. Based on the stratigraphic dip, the directional components consistent with the imaging point are selected for cross-correlation calculation to construct the conditions for elastic wave reverse time migration imaging.
It significantly improves the imaging continuity and resolution of steeply dipping structures and subsalt boundaries, reduces component leakage, maintains imaging stability and fidelity of the real structure, and effectively suppresses low-frequency noise and gradient artifacts, especially in complex media.
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Figure CN122131385A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of seismic exploration, in particular to an elastic wave reverse time migration imaging method for separating guided wave fields of stratum dip angles. BACKGROUND
[0002] As a key underground detection means for oil and gas, unconventional resources, geothermal and major projects (tunnel, reservoir, carbon sequestration), etc., seismic exploration continues to evolve towards deeper targets, more complex structures and higher resolution. The supporting acquisition technology (wide azimuth / ultra-wide azimuth WAZ, ocean bottom node OBN, multi-component geophone, etc.) and high-performance computing significantly improve data quality and computing scale, and put forward higher requirements for high-fidelity imaging technology, especially in steeply dipping flanks, under salt / igneous rock, etc. Weakly illuminated areas.
[0003] In the prior art, the existing De-primary reverse time migration (Dp-RTM) method separates the wave field along the depth direction by introducing Hilbert transform, and only selects the downgoing wave at the source end and the upgoing wave at the geophone end for cross-correlation imaging, thereby effectively reducing the low-frequency noise and the turning artifacts caused by the velocity gradient while maintaining the calculation efficiency.
[0004] However, the available incidence angle aperture of the existing Dp-RTM method is significantly compressed, and the prismatic wave carried by the co-propagating related term and other multiple wave energy are also excluded, so that the illumination of steeply dipping flanks and salt boundaries is insufficient, the event is easy to break, the fixed decomposition direction of up / down is not matched with the actual stratum dip angle, and component leakage and residual artifacts are easy to occur in areas with mixed multi-dip angles or strong lateral velocity gradients, and the initial velocity error is more sensitive, resulting in that the noise reduction of the existing Dp-RTM method sacrifices part of the effective illumination, and it is difficult to balance the artifact suppression and fidelity in complex geological structures. SUMMARY
[0005] Therefore, it is necessary to provide an elastic wave reverse time migration imaging method for separating guided wave fields of stratum dip angles in view of the above technical problems.
[0006] The present application adopts the following technical solutions: The present application provides an elastic wave reverse time migration imaging method for separating guided wave fields of stratum dip angles, comprising: obtaining an initial velocity model of elastic wave propagation, source wave field data and geophone wave field data of a plurality of target local regions in a geological area; Using the vertical downward direction as the reference direction for the target local area, and based on the elastic wave propagation initial velocity model, the dip angle of the strata used to characterize the change trend of the underground structural space in each target local area is determined, and the direction pointed to by each strata dip angle is determined as the target spatial direction of the underground structural space in each target local area. Hilbert transform is performed on the source wavefield data and receiver wavefield data of each local region of the target along each target spatial direction to obtain the source wavefield components and receiver wavefield components that are consistent with the spatial directions of multiple targets. For any point to be imaged in the underground space of the target geological area, the target spatial direction of the point to be imaged is selected from all the target spatial directions according to the dip angle of the strata corresponding to the spatial location of the point to be imaged in the vertical direction. Then, the source wavefield component and the receiver wavefield component that are consistent with the target spatial direction of the point to be imaged are selected from the source wavefield component and the receiver wavefield component and zero-delay cross-correlation calculation is performed to obtain the reverse time migration imaging result of the point to be imaged.
[0007] Preferably, taking the vertically downward direction as the reference direction for the target local area, and based on the elastic wave propagation initial velocity model, the stratigraphic dip angle used to characterize the spatial variation trend of the subsurface structure in each target local area is determined, specifically including: Using the vertically downward direction as the reference direction for the target local region, determine the spatial gradient of the initial velocity model for each target local region; A two-dimensional structural tensor of the target local region is constructed based on the spatial gradient, and structural components are extracted from the two-dimensional structural tensor. The polar angle of the outer normal of each target local region is determined based on the structural components. Using the spatial gradient as the external normal polarity constraint for the target local region, the external normal dip vector of each target geological region is determined; Based on the outward normal dip vector, the dip angle of the strata used to characterize the spatial variation trend of the underground structure in the target local area is determined.
[0008] Preferably, taking the vertically downward direction as the reference direction for the target local region, the spatial gradient of the initial velocity model for each target local region is determined, and a two-dimensional structure tensor for the target local region is constructed based on the spatial gradient, specifically including: For any target local region, the initial velocity model ,calculate The spatial gradient is given by the formula: ; In the formula, The spatial gradient of the initial velocity model for the target local region. and These are the velocity gradient components in the horizontal and vertical directions of the local target region, respectively. The two-dimensional structure tensor of the local region of the target is constructed using the velocity gradient, as shown in the formula: ; In the formula, For a two-dimensional structure tensor, This represents a two-dimensional Gaussian kernel with standard deviation of R. This represents the tensor element obtained after Gaussian smoothing the product of second-order gradients.
[0009] Preferably, based on extracting structural components from the two-dimensional structural tensor, the polar angle of the outward normal of each target local region is determined according to the structural components, specifically including: The structural components are extracted from the two-dimensional structural tensor, and the polar angle of the external normal to the local region of the target and its corresponding unit normal vector are calculated using the two-parameter arctangent function, as follows: ; In the formula, Let n represent the polar angle of the outer normal of a local region of the target, and n represent the unit normal vector corresponding to the polar angle of the outer normal of the local region of the target. arctan2( x, y ) represents the two-parameter arctangent function, used to return the angle with the correct quadrant; where the normal vectors 𝑛 and −𝑛 are mathematically equivalent, so the direction of the unit normal vector corresponding to the polar angle of the outer normal of the local region of the target cannot be uniquely determined by the structure tensor alone.
[0010] Preferably, the spatial gradient is used as the external normal polarity constraint for the target local region to determine the external normal dip vector for each target geological region, specifically including: Based on the spatial gradient and the unit normal vector corresponding to the polar angle of the outer normal of the local target region, the outer normal polarity constraint condition is constructed, and the formula is as follows: ; In the formula, for, The spatial gradient of the initial velocity model for the target local region. The unit normal vector corresponding to the polar angle of the outer normal of the local target region; Based on the aforementioned external normal polarity constraint, the direction vector of the external normal is determined using the following formula: ; In the formula, The direction vector of the outward normal; Based on the direction vector of the outer normal, the dip vector of the outer normal is determined by the following formula: ; In the formula, Let the outward normal vector of the target local region be the vector of the direction ... These are the components of the direction vectors of the outward normal of the local region of the target in the horizontal and vertical directions, respectively.
[0011] Preferably, the dip angle of the strata used to characterize the spatial variation trend of the underground structure in the target local area is determined based on the outward normal dip vector, specifically including: Based on the dip vector components of the outward normal in the horizontal and vertical directions, the dip angle of the strata, which characterizes the spatial variation trend of the subsurface structure in the target local area, is calculated using a two-parameter arctangent function. The formula is as follows: ; In the formula, The dip angle of the strata is used to characterize the spatial variation trend of the subsurface structure in a local target area. These are the horizontal and vertical components of the outward normal's dip vector, respectively.
[0012] Preferably, the source wavefield data and receiver wavefield data of each target local region are subjected to Hilbert transform along each target spatial direction to obtain source wavefield components and receiver wavefield components consistent with multiple target spatial directions. Specifically, this includes: sampling the wavefield in a one-dimensional direction along the target spatial direction and obtaining the wavefield sequence along that one-dimensional direction through interpolation; applying a one-dimensional Hilbert transform to the wavefield sequence to obtain the wavefield components propagating along that one-dimensional direction; and sampling, interpolating, and performing a one-dimensional Hilbert transform on the source wavefield and receiver wavefield respectively to obtain a set of direction components corresponding to multiple target spatial directions.
[0013] Preferably, the calculation formulas for the source wavefield components and the receiver wavefield components are as follows: ; In the formula, and These represent the spatial locations of the source wavefield or the receiver wavefield, respectively. In the The two wavefield components separated along the target space direction at each time step For spatial location In the The source wavefield or receiver wavefield at each time step For the Hilbert transform along the target space direction β, This is the Hilbert transform with respect to time t.
[0014] Preferably, the formula for calculating the reverse time migration imaging result of the point to be imaged is: ; In the formula, and The results are PP and PS imaging, respectively. This indicates that the calculation is performed using actual values. The maximum propagation time of the wave field. For the wavefield separation operator of the Hilbert transform, , and These represent the source P-wave, the receiver P-wave, and the receiver S-wave, respectively. The dip angle of the strata.
[0015] The above-mentioned at least one technical solution adopted in this invention can achieve the following beneficial effects: In the elastic wave reverse-time migration imaging method for wavefield separation guided by stratigraphic dip angle provided by this invention, for any imaging point in the underground space of a geological region, the target spatial direction of the imaging point is selected from all the target spatial directions based on the target spatial direction determined by the stratigraphic dip angle corresponding to the spatial location of the imaging point in the vertical direction. The target spatial direction determined by the stratigraphic dip angle is used to guide the wavefield decomposition direction, selecting the direction component consistent with the actual structural orientation (target spatial direction). By utilizing cross-correlation imaging conditions consistent with the dip angle, component leakage is reduced and the accuracy of direction selection is improved, enabling imaging of different structures. Adaptively selecting wavefield components with matching directions for imaging prioritizes the suppression of low-frequency noise and gradient artifacts in geological structures with small or medium dip angles. Particularly in steeply dipping / nearly vertical geological structures, employing cross-correlation of forward and reverse propagating wavefields corresponding to the dip angle significantly improves the continuity of the in-phase axis and the clarity of the salt body's flanks and subsalt boundaries. Simultaneously, it preserves effective illumination energy such as prisms and gyratory waves, enabling elastic wave reverse-time migration in complex media to achieve both artifact suppression and fidelity preservation. This effectively enhances the imaging continuity and resolution of steeply dipping structures and subsalt boundaries, maintaining the amplitude and phase stability of elastic PP / PS imaging. This method should possess good engineering feasibility and scalability, seamlessly embedding into existing pre-stack elastic migration pipelines and facilitating the widespread application of 2D / 3D and heterogeneous parallel computing. Attached Figure Description
[0016] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:
[0017] Figure 1 A schematic flowchart of an elastic wave reverse time migration imaging method for formation dip-guided wavefield separation provided by the present invention; Figure 2 A schematic diagram of structural imaging path analysis for different dip angles in an elastic wave reverse time migration imaging method for formation dip angle guided wavefield separation provided by the present invention. Figure 3 A schematic diagram illustrating the determination of the formation dip angle in an elastic wave reverse time migration imaging method for formation dip angle-guided wavefield separation provided by the present invention. Figure 4 A schematic diagram of multi-directional traveling wave separation data sampling and interpolation for an elastic wave reverse time migration imaging method for formation dip-guided wavefield separation provided by the present invention; Figure 5 A schematic diagram of wave field decomposition for point source propagation in a homogeneous medium in an elastic wave reverse time migration imaging method with formation dip-guided wave field separation provided by the present invention. Figure 6 A schematic diagram of the BP model for an elastic wave reverse time migration imaging method for formation dip-guided wavefield separation provided by the present invention; Figure 7 The BP model imaging results of an elastic wave reverse time migration imaging method for formation dip-guided wavefield separation provided by the present invention; Figure 8 The white dashed box area represents the imaging result of an elastic wave reverse time migration imaging method for stratigraphic dip-guided wavefield separation provided by this invention. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in the specification without creative effort are within the scope of protection of this application.
[0019] To overcome the limitations of existing technologies in achieving both noise reduction and fidelity preservation in complex media, this invention proposes a multi-directional wavefield decomposition ERTM imaging method guided by stratigraphic dip angle. This method introduces stratigraphic dip angle constraints into the wavefield decomposition direction and cross-correlation imaging conditions: adaptively selecting directional components matching the dip angle for different structures to participate in cross-correlation, thereby suppressing low-frequency noise and velocity gradient artifacts while preserving as much energy as possible for illuminating prisms, gyratory waves, etc., under steep dips / salt.
[0020] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.
[0021] Figure 1 This is a schematic diagram of the elastic wave reverse time migration imaging method for formation dip-guided wavefield separation according to the present invention, which specifically includes the following steps: S101: Acquire initial velocity models, source wavefield data, and receiver wavefield data for multiple target local areas in a geological region.
[0022] S102: Taking the vertical downward direction as the reference direction of the target local area, based on the elastic wave propagation initial velocity model, determine the stratum dip angle used to characterize the underground structural space change trend of each target local area, and determine the direction pointed to by each stratum dip angle as the target space direction of the underground structural space of each target local area. Optionally, taking the vertically downward direction as the reference direction for the target local area, and based on the elastic wave propagation initial velocity model, the dip angle of the strata used to characterize the spatial variation trend of the subsurface structure in each target local area is determined. Specifically, this includes: taking the vertically downward direction as the reference direction for the target local area, determining the spatial gradient of the initial velocity model for each target local area; constructing a two-dimensional structural tensor for the target local area based on the spatial gradient, and extracting structural components from the two-dimensional structural tensor; determining the polar angle of the external normal for each target local area based on the structural components; determining the external normal dip vector for each target geological area using the spatial gradient as the external normal polarity constraint for the target local area; and determining the dip angle of the strata used to characterize the spatial variation trend of the subsurface structure in the target local area based on the external normal dip vector.
[0023] Optionally, taking the vertically downward direction as the reference direction, the spatial gradient of the initial velocity model of each target local region is determined, and a two-dimensional structure tensor of the target local region is constructed based on the spatial gradient. Specifically, this includes: for any target local region, the initial velocity model... ,calculate The spatial gradient is given by the formula: ; In the formula, The spatial gradient of the initial velocity model for the target local region. and These are the velocity gradient components in the horizontal and vertical directions of the local target region, respectively.
[0024] The two-dimensional structure tensor of the local region of the target is constructed using the velocity gradient, as shown in the formula: ; In the formula, For a two-dimensional structure tensor, This represents a two-dimensional Gaussian kernel with standard deviation of R. This represents the tensor element obtained after Gaussian smoothing the product of second-order gradients.
[0025] Optionally, based on the structural components in the two-dimensional structural tensor, the polar angle of the external normal of each target local region is determined. Specifically, this includes: extracting the structural components from the two-dimensional structural tensor, and calculating the polar angle of the external normal of the target local region and its corresponding unit normal vector using a two-parameter arctangent function, as shown in the formula: ; In the formula, Let n represent the polar angle of the outer normal of a local region of the target, and n represent the unit normal vector corresponding to the polar angle of the outer normal of the local region of the target. arctan2( x, y ) represents the two-parameter arctangent function, used to return the angle with the correct quadrant; where the normal vectors 𝑛 and −𝑛 are mathematically equivalent, so the direction of the unit normal vector corresponding to the polar angle of the outer normal of the local region of the target cannot be uniquely determined by the structure tensor alone.
[0026] Optionally, the spatial gradient is used as the external normal polarity constraint for the target local region to determine the external normal dip vector for each target geological region. Specifically, this includes constructing external normal polarity constraint conditions based on the spatial gradient and the unit normal vector corresponding to the external normal polar angle of the target local region, as shown in the formula: ; In the formula, for, The spatial gradient of the initial velocity model for the target local region. The unit normal vector corresponding to the polar angle of the outer normal of the local target region; Based on the aforementioned external normal polarity constraint, the direction vector of the external normal is determined using the following formula: ; In the formula, The direction vector of the outward normal; Based on the direction vector of the outer normal, the dip vector of the outer normal is determined by the following formula: ; In the formula, Let the outward normal vector of the target local region be the vector of the direction ... These are the components of the direction vectors of the outward normal of the local region of the target in the horizontal and vertical directions, respectively.
[0027] Optionally, based on the outward normal dip vector, the dip angle of the strata used to characterize the spatial variation trend of the subsurface structure in the target local area is determined. Specifically, this includes: calculating the dip angle of the strata used to characterize the spatial variation trend of the subsurface structure in the target local area using a two-parameter arctangent function based on the dip vector components of the outward normal dip vector in the horizontal and vertical directions, as shown in the formula: ; In the formula, The dip angle of the strata is used to characterize the spatial variation trend of the subsurface structure in a local target area. These are the horizontal and vertical components of the outward normal's dip vector, respectively.
[0028] S103: Perform Hilbert transformation on the source wavefield data and receiver wavefield data of each target local area along each target spatial direction to obtain the source wavefield components and receiver wavefield components that are consistent with the spatial directions of multiple targets.
[0029] Optionally, the source wavefield data and receiver wavefield data are subjected to Hilbert transform along each target spatial direction to obtain source wavefield components and receiver wavefield components consistent with multiple target spatial directions. Specifically, this includes: sampling the wavefield in a one-dimensional direction along the target spatial direction and obtaining the wavefield sequence along that one-dimensional direction through interpolation; applying a one-dimensional Hilbert transform to the wavefield sequence to obtain the wavefield components propagating along that one-dimensional direction; and sampling, interpolating, and performing a one-dimensional Hilbert transform on the source wavefield and receiver wavefield respectively to obtain a set of direction components corresponding to multiple target spatial directions.
[0030] The formula for calculating the wave field components is as follows: ; In the formula, and These represent the spatial locations of the source wavefield or the receiver wavefield, respectively. In the The two wavefield components separated along the target space direction at each time step For spatial location In the The source wavefield or receiver wavefield at each time step For the Hilbert transform along the target space direction β, This is the Hilbert transform with respect to time t.
[0031] Specifically, to align multi-directional wavefield separation and cross-correlation imaging with the true structure, the dip field is first calculated from the reference field (initial velocity model or pre-migration imaging) so that cross-correlation components can be selected subsequently based on the formation dip. For example... Figure 3 As shown, stratigraphic polarity information is introduced to further constrain the subsalt boundary imaging. To achieve wavefield separation matching the stratigraphic dip angle, this paper, based on up-and-down wave separation using the Hilbert transform, further refines the wavefield data along the spatial direction. β For resampling and interpolation, see [link to documentation]. Figure 4 And apply a one-dimensional Hilbert transform.
[0032] To verify the effectiveness of the above wavefield decomposition method, a homogeneous medium model with a size of 4 km × 4 km and a grid step size of 10 m was selected for numerical modeling. At the center of the domain ( x , zA single-pole source was established at (2000 m, 2000 m), with a 15 Hz Ricker wavelet. The wavefield propagation was simulated by solving the two-way wave equation using the finite difference method; the time sampling interval was 4 ms, and the total simulation duration was 2 s. Subsequently, directional decomposition was performed on the synthetic data along seven representative azimuths, such as... Figure 5 As shown in the figure. The results show that this method can stably extract the traveling wave component in the target direction in all directions and maintain good phase and amplitude fidelity, laying the foundation for subsequent tilt-guided cross-correlation imaging.
[0033] S104: For any point to be imaged in the underground space of the target geological area, based on the dip angle of the strata corresponding to the spatial location of the point to be imaged in the vertical direction, select the target spatial direction of the point to be imaged from all the target spatial directions, and select the source wavefield component and the receiver wavefield component that are consistent with the target spatial direction of the point to be imaged from the source wavefield component and the receiver wavefield component, and perform zero-delay cross-correlation calculation to obtain the reverse time migration imaging result of the point to be imaged.
[0034] Optionally, the formula for calculating the reverse time migration imaging result of the point to be imaged is: ; In the formula, and The results are PP and PS imaging, respectively. This indicates that the calculation is performed using actual values. The maximum propagation time of the wave field. For the wavefield separation operator of the Hilbert transform, , and These represent the source P-wave, the receiver P-wave, and the receiver S-wave, respectively. The dip angle of the strata.
[0035] Specifically, to verify the depth imaging capability of this method under conditions close to real-world complexity, the BP model was selected as a numerical example. The main challenge of this model lies in the accurate imaging of the flanks of steeply sloping salt bodies, which traditional Dp-ERTM methods often fail to adequately capture. The actual P-wave velocity, S-wave velocity, and migrated P-wave velocity models used in the experiment are shown in [reference needed]. Figure 6 of (a), Figure 6 (b) and Figure 6 (c); The shot gather is generated by forward modeling of the real model, and the dip angle information is obtained by the initial velocity model based on the structure tensor estimation, such as Figure 6 As shown in (d), the computational grid consisted of 1200 × 400 elements; a total of 120 shots were simulated, with a source spacing of 150 m. Each shot was recorded by 1000 geophones spaced at 15 m intervals. The source used a 12 Hz Ricker wavelet with a time sampling interval of 2 m, and the total recording time was 16 s.
[0036] Figure 6 Imaging comparisons of three methods (traditional ERTM, Dp-ERTM, and the method proposed in this invention) on the BP model are presented. Traditional ERTM can recover the main stratigraphic framework, but it suffers from significant low-frequency noise and velocity gradient artifacts, such as... Figure 7 (a) and Figure 7 As shown in (b); Dp-ERTM provides clear imaging of near-horizontal reflectors, but insufficient illumination of the salt body's flanks, such as... Figure 7 (c) and Figure 7 As shown in (d); the method of the present invention can simultaneously suppress low-frequency and gradient-induced artifacts, and achieve better continuity and boundary clarity at the steeply sloping flank and salt substrate interface (see Figure 7(e) and 7(d)). Figure 7 (f) Figure 8 for Figure 7 The enlarged view of the area within the white dashed box further demonstrates the improvement in image quality.
[0037] The effectiveness of the method of the present invention was verified by comparing the imaging results. The method guides the wavefield separation direction by using the dip angle of the strata, and then constructs the elastic wave reverse time migration imaging conditions to ensure that the elastic wave reverse time migration algorithm can be used to image vertical steep structures and subsalt boundaries while removing artifacts.
[0038] This invention addresses the challenge of simultaneously suppressing artifacts and preserving fidelity in elastic wave reverse-time migration within complex media. It proposes a novel approach that uses the formation dip angle as a priori and aligns the wavefield decomposition direction with cross-correlation imaging conditions. This scheme effectively suppresses low-frequency noise and velocity gradient artifacts while preserving the energy of prisms and gyratory waves to enhance illumination and continuity at steeply dipped flanks and subsalt boundaries. Overall imaging resolution and stability are significantly improved, demonstrating good engineering feasibility and widespread application value.
[0039] This paper proposes an arbitrary-direction wavefield decomposition based on the Hilbert transform and aligned with the stratigraphic dip angle. Compared with traditional up-and-down wave separation that uses the vertical direction as a reference, this invention resamples the wavefield according to the stratigraphic dip angle and applies a one-dimensional Hilbert analytical transform to construct directional components consistent with the actual structural orientation, thereby reducing component leakage and improving the accuracy of direction selection.
[0040] A dip-guided cross-correlation imaging condition is proposed. At each imaging point, based on the formation dip information, the source / detector direction components consistent with the dip angle are adaptively selected for zero-delay cross-correlation: at small to medium dip angles, low-frequency noise and gradient artifacts are preferentially suppressed; at steeply dipped / nearly vertical structures, forward and reverse propagation wavefield cross-correlation corresponding to the dip angle is adopted, significantly improving the in-phase axis continuity and boundary sharpness of the salt body flanks and subsalt boundaries. This better maintains imaging fidelity and amplitude-phase stability while ensuring artifact suppression.
[0041] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this invention.
Claims
1. A method for elastic wave reverse-time migration imaging guided by stratigraphic dip angle for wavefield separation, characterized in that, include: Acquire the initial velocity model of elastic wave propagation, source wavefield data, and receiver wavefield data for multiple target local areas in a geological region; Using the vertical downward direction as the reference direction for the target local area, and based on the elastic wave propagation initial velocity model, the dip angle of the strata used to characterize the change trend of the underground structural space in each target local area is determined, and the direction pointed to by each strata dip angle is determined as the target spatial direction of the underground structural space in each target local area. Hilbert transform is performed on the source wavefield data and receiver wavefield data of each local region of the target along each target spatial direction to obtain the source wavefield components and receiver wavefield components that are consistent with the spatial directions of multiple targets. For any point to be imaged in the underground space of the target geological area, the target spatial direction of the point to be imaged is selected from all the target spatial directions according to the dip angle of the strata corresponding to the spatial location of the point to be imaged in the vertical direction. Then, the source wavefield component and the receiver wavefield component that are consistent with the target spatial direction of the point to be imaged are selected from the source wavefield component and the receiver wavefield component and zero-delay cross-correlation calculation is performed to obtain the reverse time migration imaging result of the point to be imaged.
2. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 1, characterized in that, The reference direction for the target local area is vertically downward. Based on the elastic wave propagation initial velocity model, the dip angle of the strata used to characterize the spatial variation trend of the underground structure in each target local area is determined, specifically including: Using the vertically downward direction as the reference direction for the target local region, determine the spatial gradient of the initial velocity model for each target local region; A two-dimensional structural tensor of the target local region is constructed based on the spatial gradient, and structural components are extracted from the two-dimensional structural tensor. The polar angle of the outer normal of each target local region is determined based on the structural components. Using the spatial gradient as an external normal polarity constraint for the target local region, the external normal dip vector of each target geological region is determined. Based on the outward normal dip vector, the dip angle of the strata used to characterize the spatial variation trend of the underground structure in the target local area is determined.
3. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 2, characterized in that, The process involves determining the spatial gradient of the initial velocity model for each target local region, using the vertically downward direction as the reference direction, and constructing a two-dimensional structure tensor for the target local region based on the spatial gradient. Specifically, this includes: For any target local region, the initial velocity model ,calculate The spatial gradient is given by the formula: ； In the formula, The spatial gradient of the initial velocity model for the target local region. and These are the velocity gradient components in the horizontal and vertical directions of the local target region, respectively. The two-dimensional structure tensor of the local region of the target is constructed using the velocity gradient, as shown in the formula: ； In the formula, For a two-dimensional structure tensor, This represents a two-dimensional Gaussian kernel with standard deviation of R. This represents the tensor element obtained after Gaussian smoothing the product of second-order gradients.
4. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 2, characterized in that, Based on extracting structural components from the two-dimensional structural tensor, the polar angle of the external normal of each target local region is determined according to the structural components, specifically including: The structural components are extracted from the two-dimensional structural tensor, and the polar angle of the external normal to the local region of the target and its corresponding unit normal vector are calculated using the two-parameter arctangent function, as follows: ； In the formula, Let n represent the polar angle of the outer normal of a local region of the target, and n represent the unit normal vector corresponding to the polar angle of the outer normal of the local region of the target. arctan2( x,y ) represents the two-parameter arctangent function, used to return the angle with the correct quadrant; where the normal vectors 𝑛 and −𝑛 are mathematically equivalent, so the direction of the unit normal vector corresponding to the polar angle of the outer normal of the local region of the target cannot be uniquely determined by the structure tensor alone.
5. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 2, characterized in that, Using the spatial gradient as the external normal polarity constraint for the target local region, the external normal dip vector of each target geological region is determined, specifically including: Based on the spatial gradient and the unit normal vector corresponding to the polar angle of the outer normal of the local target region, the outer normal polarity constraint condition is constructed, and the formula is as follows: ； In the formula, for, The spatial gradient of the initial velocity model for the target local region. The unit normal vector corresponding to the polar angle of the outer normal of the local target region; Based on the aforementioned external normal polarity constraint, the direction vector of the external normal is determined using the following formula: ； In the formula, The direction vector of the outward normal; Based on the direction vector of the outer normal, the dip vector of the outer normal is determined by the following formula: ； In the formula, Let the outward normal vector of the target local region be the vector of the direction ... These are the components of the direction vectors of the outward normal of the target local region in the horizontal and vertical directions, respectively.
6. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 2, characterized in that, Based on the outward normal dip vector, the dip angle of the strata used to characterize the spatial variation trend of the subsurface structure in the target local area is determined, specifically including: Based on the dip vector components of the outward normal in the horizontal and vertical directions, the dip angle of the strata, which characterizes the spatial variation trend of the subsurface structure in the target local area, is calculated using a two-parameter arctangent function. The formula is as follows: ； In the formula, The dip angle of the strata is used to characterize the spatial variation trend of the subsurface structure in a local target area. These are the horizontal and vertical components of the outward normal's dip vector, respectively.
7. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 1, characterized in that, The process of performing Hilbert transform on the source wavefield data and receiver wavefield data of each target local region along each target spatial direction to obtain source wavefield components and receiver wavefield components consistent with multiple target spatial directions specifically includes: sampling the wavefield in a one-dimensional direction along the target spatial direction and obtaining the wavefield sequence along that one-dimensional direction through interpolation; applying a one-dimensional Hilbert transform to the wavefield sequence to obtain the wavefield components propagating along that one-dimensional direction; and sampling, interpolating, and performing a one-dimensional Hilbert transform on the source wavefield and receiver wavefield respectively to obtain a set of direction components corresponding to multiple target spatial directions.
8. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 7, characterized in that, The calculation formulas for the source wavefield components and receiver wavefield components are as follows: ； In the formula, and These represent the spatial locations of the source wavefield or the receiver wavefield, respectively. In the The two wavefield components separated along the target space direction at each time step For spatial location In the The source wavefield or receiver wavefield at each time step For the Hilbert transform along the target space direction β, This is the Hilbert transform with respect to time t.
9. The elastic wave reverse-time migration imaging method for stratigraphic dip-guided wavefield separation as described in claim 1, characterized in that, The formula for calculating the reverse time-shifted imaging result of the point to be imaged is: ； In the formula, and The results are PP and PS imaging, respectively. This indicates that the calculation is performed using actual values. The maximum propagation time of the wave field. For the wavefield separation operator of the Hilbert transform, , and These represent the source P-wave, the receiver P-wave, and the receiver S-wave, respectively. The dip angle of the strata.