OBN or OBS exploration shear wave data conversion method based on seismic interference method

Abstract

The invention discloses an OBN or OBS exploration transverse wave data conversion method based on a seismic interference method, and belongs to the field of geophysical exploration and seismology, and the method comprises the steps: carrying out the longitudinal and transverse wave field separation of collected original X-component and Z-component seismic data, so as to separate the original seismic data into longitudinal waves (PP waves) and converted waves (PS waves); the method comprises the following steps: selecting sea surface shot points and a seabed detector, respectively carrying out cross-correlation operation on direct waves, PP waves and PS waves received by the seabed detector by using a seismic interference method, and obtaining virtual source PP wave and PS wave records of which shot points are all located at the seabed; the method aims to eliminate the influence of a water layer and obtain virtual source records with shot points located at the seabed. And based on the obtained virtual source record of the shot detection point at the seabed, carrying out second interference method processing on the reflected wave, namely obtaining the virtual source record of the SS wave by combining the PP wave and the PS wave, and then finally obtaining the section of the virtual source SS wave by using a conventional longitudinal wave data processing method.

Description

Technical Field

[0001] The invention belongs to the field of geophysical exploration and seismology, and in particular relates to a method for converting shear wave data of OBN or OBS exploration based on seismic interferometry. Background Art

[0002] In marine oil and gas exploration, the two exploration methods of OBN and OBS are increasingly being used in actual acquisition. Therefore, how to process the data collected by the two methods has always been a hot issue. In the existing PS wave interferometry method, longitudinal wave data is mainly used for processing. As seismic waves are reflected when they encounter interfaces during propagation, they will also decompose at the interfaces. Therefore, during the propagation process, longitudinal waves will also be decomposed into transverse waves, and then continue to propagate in the form of transverse waves, further decomposed into longitudinal waves at the solid-liquid interface for propagation, and finally received by the detector on the water surface. However, in the actual received longitudinal wave signal, the energy of this wave field is weak and difficult to identify, so the existing PS wave interferometry method is difficult to apply in actual data processing.

[0003] This method is based on the application of the existing seismic interferometry method in conventional longitudinal wave data processing, and proposes a new data processing method that can be applied to the data collected by both OBN and high-density OBS exploration methods, thereby further expanding the application scope of the seismic interferometry method. Summary of the invention

[0004] The present invention aims to solve the technical problems existing in the background technology and provides a method for converting shear wave data of OBN or OBS exploration based on seismic interferometry.

[0005] In order to solve the technical problem, the technical solution of the present invention is:

[0006] A method for converting shear wave data of OBN or OBS exploration based on seismic interferometry, the method comprising:

[0007] S1: Separate the P-wave and S-wave fields of the collected original X-component and Z-component seismic data to obtain PP waves and PS waves;

[0008] S2: Select sea surface shot points and seabed geophones, use seismic interferometry to perform cross-correlation operations on the direct waves, PP waves and PS waves received by the seabed geophones, and obtain virtual source PP wave and PS wave records when the shot points are all located on the seabed;

[0009] S3: Based on the virtual source record of the gun check point located on the seabed, the reflected wave is processed by the second interference method, PP+PS=SS, that is, the virtual source record of the SS wave is obtained by combining the PP wave and the PS wave. Then, the conventional longitudinal wave data processing method is used to finally obtain the profile of the virtual source SS wave.

[0010] Further, the step S2 specifically includes:

[0011] Perform cross-correlation operation on the xAOB and yOB data to eliminate the time of the seismic wave propagation path in the water, and finally obtain the seismic record with A as the virtual source and B as the receiver;

[0012] The principle of the method is shown in the following formula:

[0013]

[0014] Among them, x and y are the shot points on the water surface, and A and B are the detectors on the seabed.

[0015] xAOB and yOB represent two seismic data records. Here, x and y are the shot points on the water surface, and A and B are the detectors on the seafloor. "xAOB" and "yOB" represent the records of seismic waves emitted from the two shot points x and y at the two detectors A and B, respectively.

[0016] In seismic exploration, a shot point is the location of the seismic wave source, and a geophone is a device that receives seismic waves. By analyzing the records of seismic waves emitted from different shot points at different geophones, information about underground structures can be obtained. In the present invention, the two data xAOB and yOB are cross-correlated, the time of the seismic wave propagation path in water is eliminated, and finally a seismic record is obtained in which A is the virtual source and B is the receiving. This is a key step in seismic interferometry, which can effectively improve the accuracy of seismic data processing.

[0017] Further, the step S3 specifically includes:

[0018] Step 1: Perform interference processing on the two data of AOB and AON. After cross-correlation operation, eliminate the incident wave part AO and obtain BN;

[0019] Step 2: In the first step, N is the record of the virtual source point. Then, N is taken as the shot point, and M is the PS wave NM received by the detector. BN and NM are cross-correlated, and the common path NO is eliminated. Finally, BM is obtained. This result can be regarded as B is the virtual source point and M is the virtual source record of the detector.

[0020] In the record, point B is the shear wave source excitation, and point M is the received SS wave signal; the principle formula of the method is as follows:

[0021] ω ψS (t,M,B)=∫∫[ω PS (t,A,B)*ω PS (t,N,M)*ω PP (-t,A,N)]dAdN (2)

[0022] Among them, M and N are both seabed detectors.

[0023] AOB and AON represent two seismic data records. Here, A is a virtual shot point on the seafloor, and B and N are the detectors on the seafloor. "AOB" and "AON" represent the records of seismic waves emitted from point A as a virtual shot point at the two detectors B and N, respectively.

[0024] In seismic exploration, a virtual shot point is a virtual source position obtained by seismic interferometry, and a geophone is a device that receives seismic waves. By analyzing the records of seismic waves emitted from different virtual shot points at different geophones, information about underground structures can be obtained. In the present invention, the two data AOB and AON are processed by interferometry, and after cross-correlation operation, the incident wave part AO is eliminated to obtain BN. Then, N is used as the shot point, and M is the PS wave NM received by the geophone. BN and NM are cross-correlated, and the common path NO is eliminated, and BM is finally obtained. This is a key step in seismic interferometry, which can effectively improve the accuracy of seismic data processing.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] (1) The existing interferometry processing method cannot be applied to data processing when the shot check points are not located in the same plane. In the present invention, it can be applied to high-density OBS exploration and OBN exploration data processing, which can eliminate the influence of the seawater layer and make the application scenario of seismic interferometry more extensive.

[0027] (2) Both OBS and OBN are four-component detectors, specifically including a P component for receiving longitudinal wave information, a Z component for mainly receiving longitudinal waves, and two X and Y components for receiving transverse wave information. In the existing interference method, the P component data is mainly processed, and the data of the other three components are not used. The present invention uses the X component and the Z component for processing, fully utilizes the PS wave data, and the result is more accurate.

[0028] (3) Using this method, a virtual source record similar to the result of the longitudinal wave interferometry method can be obtained. In this way, in the subsequent processing, the conventional longitudinal wave data processing flow can be used for processing, which is convenient and fast, and can quickly image, providing a reference for subsequent data analysis and interpretation. The biggest difference between the virtual source record generated by the method proposed in the present invention and the existing PS wave interferometry method is that its result represents the virtual source S wave excitation S wave reception, that is, the obtained virtual source record fully represents the shear wave information, and the constructed S wave velocity can be directly obtained, eliminating the velocity iteration process in the conventional processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 , Existing technology PPSP wave and PS wave interference method;

[0030] Figure 2 , the PS wave seismic interferometry method proposed by the present invention;

[0031] Figure 3 , PS wave interferometry processing flow;

[0032] Figure 4 , construct geological model 1;

[0033] Figure 5 , virtual source record corresponding model;

[0034] Figure 6 , model forward Z component (a) and X component (b) data;

[0035] Figure 7 , PP wave (a) and PS wave (b) after separation;

[0036] Figure 8 , (a) PP wave virtual source record obtained by the first interferometry method; (b) PP wave record obtained by model forward modeling;

[0037] Fig. 9 , (a) PS wave virtual source record obtained by the first interferometry method; (b) PS wave record obtained by model forward modeling;

[0038] Fig.10 , build a horizontal model;

[0039] Fig.11 , model forward simulation of PP wave (a) and PS wave (b);

[0040] Fig.12 , virtual source SS wave seismic records;

[0041] Fig.13 , virtual source SS wave superposition profile;

[0042] Fig.14 , X-component data after removing the refracted wave;

[0043] Fig.15 , Z component data after removing the refracted wave;

[0044] Fig.16 , Ps wave after separation of longitudinal and transverse waves;

[0045] Fig.17 , PP wave after separation of longitudinal and transverse waves;

[0046] Fig.18 , the first interference calculation result of the direct wave and the separated PP wave;

[0047] Fig.19 , the first interference calculation result of the direct wave and the separated PS wave;

[0048] Fig. 20 , actual data processing to obtain virtual source SS wave records. DETAILED DESCRIPTION

[0049] The specific implementation mode of the present invention is described below in conjunction with embodiments:

[0050] It should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to match the contents disclosed in the specification so that people familiar with this technology can understand and read them, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0051] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0052] Definitions of Abbreviations and Key Terms:

[0053] OBN: Ocean Bottom Node;

[0054] OBS: Ocean Bottom Seismograph;

[0055] CMP: common centroid point;

[0056] PS wave: converted shear wave;

[0057] P wave: longitudinal wave;

[0058] S wave: transverse wave;

[0059] Embodiment 1:

[0060] In the existing technology, when seismic longitudinal wave signals are propagating, they can propagate in any medium of solid, liquid, or gas state, so seismic interferometry has a relatively mature application in the data processing of PP waves. However, in the data application of PS waves, since S waves cannot propagate in fluids, and at the same time, when the waves are reflected at the interface, the angle of incidence and the angle of reflection are no longer equal, seismic interferometry is relatively less used in the application of PS waves. The figure below is a processing method proposed by Ma in 2022. The main principles of the method used are as follows: Figure 1 shown.

[0061] In the figure, S1 and S2 are the shot points at the sea surface, and R is the detector at the sea surface. When the S1 shot point is excited, the seismic wave first propagates in the seawater in the form of a P wave, and after reaching the seabed, it still transmits downward in the form of a P wave. After encountering the reflection interface, it is reflected at the interface in the form of a converted shear wave, and finally reaches the seabed-seawater interface, where the seismic wave continues to convert and propagates upward in the form of a P wave. The reflected signal is finally received by the shot point on the sea surface, and the wave field composition of the signal includes PPSP waves. When the S2 shot point is excited, the wave propagates in the seawater, reflects at the seabed, and finally the signal is received by the detector, and its wave field composition includes PP waves.

[0062] When processing, this method performs cross-correlation calculation on the signals excited by the two seismic sources S1 and S2 received by the geophone, which can eliminate the time corresponding to the wave propagation path in the water and obtain a virtual source PS wave record where both the shot point and the geophone point are located on the seabed. By completing other shot point calculations in sequence, a complete virtual source record can be obtained.

[0063] The above-mentioned existing methods mainly have the following disadvantages:

[0064] (1) The shot check points in this method are all located on the sea surface, which is suitable for processing marine streamer seismic data. It cannot process OBS and OBN data in marine seismic exploration. Therefore, this method has certain limitations.

[0065] (2) During the processing, it is impossible to determine whether there is converted shear wave in the data. In the observation system corresponding to this method, the received seismic signals are usually mainly P-wave data, and it is difficult to identify PPSP signals. Compared with OBS and OBN exploration, the X and Y components of the geophone can receive converted shear wave data.

[0066] (3) As can be seen from the principle diagram, the result obtained by this method is a single-channel virtual source record, and a complete seismic record of a virtual source point cannot be obtained. In subsequent processing, it cannot be processed using the conventional processing flow. The result obtained by the existing method is still a conventional PS wave, and the shear wave velocity of the formation cannot be directly obtained. In subsequent data processing, it is consistent with the existing PS wave processing method.

[0067] Based on the existing application methods and combined with the application of seismic interferometry in ocean P-wave data processing, a new PS wave seismic interferometry method is proposed. Figure 2 As shown:

[0068] In the figure, x and y are the shot points on the water surface, A, B, M and N are the detectors on the seabed, P represents the longitudinal wave propagating downward, and S1 and S2 represent the transverse waves generated by the conversion. This method is divided into two steps when processing data.

[0069] The first step is to use seismic interferometry to process the primary reflection and direct wave, in order to obtain a virtual source record where the shot checkpoints are all located on the seabed. That is, the two data xAOB and yOB in the figure are cross-correlated. According to the principle, the time of the seismic wave propagation path in the water can be eliminated, and finally a seismic record with A as the virtual source and B as the receiver is obtained. The principle of the method is shown in the following formula:

[0070]

[0071] On the basis of the first step, the second step of calculation is carried out. At this time, the shot detection points are all located on the seabed. In the figure, A is the detector on the seabed. After the first step of calculation, point A is also a virtual shot point in the virtual source record. The virtual source record of point A includes the PS wave shown by AOB and the PP wave shown by AON. A new processing method is used in the subsequent calculation, namely PP+PS=SS. The principle is to combine the PP wave and the PS wave to obtain the virtual source record of the SS wave. The specific processing flow includes two parts. The first part is to perform interference processing on the two data AOB and AON. After cross-correlation operation, the incident wave part AO is eliminated to obtain BN. In the first step of calculation, N can be obtained as a record of the virtual source point. Subsequently, N is used as the shot point, and M is the PS wave NM received by the detector. BN and NM are cross-correlated to eliminate the common path NO, and finally BM is obtained. This result can be regarded as a virtual source record of B as the virtual source point and M as the detector. In the record, it can be considered that the shear wave source at point B is excited and the SS wave signal is received at point M. The principle formula of the method is shown as follows:

[0072] ω ψS (t,M,B)=∫∫[ω PS (t,A,B)*ω PS (t,N,M)*ω PP (-t,A,N)]dAdN (2)

[0073] The above is the new PS wave interference method proposed in the present invention. Compared with the methods mentioned in the prior art, this method can be applied to OBN data processing or high-density OBS data processing.

[0074] Embodiment 2:

[0075] This embodiment proposes a PS wave interference method processing flow:

[0076] In the process of processing, through understanding the principle, the relevant processing is programmed and the following processing flow is formulated to realize the processing of data and process the obtained virtual source records for imaging. Figure 3 shown.

[0077] The process of PS wave interferometry for OBS or OBN data is shown in the figure. This method processes the collected X-component and Z-component data. In actual acquisition, the geophone is affected by the flow of seawater when it is placed, and the posture of the geophone will also change, causing the geophone to be disturbed when recording. The vertical component will record some shear waves, and the horizontal geophone will also record some longitudinal waves. Therefore, it is necessary to separate the longitudinal and shear waves of the two components to obtain PP waves and PS waves. Subsequently, the data is subjected to seismic interferometry.

[0078] The operation of seismic interferometry is mainly divided into two steps. First, the interferometry is used to calculate the direct wave, PP wave and PS wave respectively, and the virtual source PP wave and PS wave records with the shot check points located on the seabed are obtained. The purpose of this step is to eliminate the influence of the water layer. After all the record operations are completed, the second interferometry processing is performed. In this operation, the direct wave is not used as the processing target, and only the reflected wave is processed. Select the appropriate detector and virtual source shot point, perform two interferometry operations, and finally obtain a single-channel virtual source record, so as to complete other detectors, and finally obtain the virtual source SS wave record corresponding to the data. Since the virtual source record represents the shear wave source exciting the shear wave reception, it can be processed using the conventional longitudinal wave data processing process to finally obtain the profile of the virtual source SS wave.

[0079] Embodiment 3:

[0080] Before applying to actual data, the feasibility of this method needs to be verified. Therefore, the model data needs to be processed first. In the process of demonstration, two simple small models are used for verification. The two models correspond to two processing steps respectively. Model 1 is as follows Figure 4 shown.

[0081] There are 401 gun points in the model, with a gun spacing of 12.5 meters, and 201 detectors are deployed on the seabed with a spacing of 12.5 meters. There are two reflection interfaces under the seabed. In this model, the first step of this method is mainly demonstrated, that is, the use of direct waves and PP waves and PS waves for processing. When processing the model data, the data is first separated by longitudinal and transverse waves, and then processed by interference method. After processing, the purpose is to obtain virtual source records where all gun detection points are located on the seabed. The model corresponding to the virtual source record becomes as follows Figure 5 shown.

[0082] First of all Figure 3 The forward model data is processed. Figure 6 (a) is the Z component data of the forward modeling, and (b) is the X component data. The data is then separated into longitudinal and transverse waves, and shot-check conversion is performed to facilitate subsequent processing. Figure 7 (a) is the PP wave after separation, and (b) is the PS wave.

[0083] The direct wave is picked up from the separated data and the first interferometry operation is performed. The purpose of this step is to obtain a virtual source record where all the shot check points are located on the seabed. Figure 7 is the result of the first interference method operation. In order to better test the accuracy of the method, Figure 4 The model shown is forward modeled and the forward modeling results are compared. Figure 8 (a) is the PP wave virtual source record obtained after the first interferometric processing, (b) is Figure 5 PP wave records obtained after forward modeling and decomposition. Fig. 9 (a) is the PS wave virtual source record obtained after the first interferometric processing, (b) is Figure 5 PS wave record obtained after forward modeling and decomposition. By comparing the two results, it can be found that, except for the direct wave, the other two interface reflections are basically consistent in time, so it can be considered that the result of the first interference method is relatively accurate, and the method principle of this step is basically established.

[0084] In the proposed method, two seismic interferometry operations are required. The principle of the first interferometry has been demonstrated above, and the second interferometry will be demonstrated later. For this purpose, a horizontal model is re-established, such as Fig.10 As shown. There are 201 shot points and 201 receiver points in the model, and their positions are consistent and the spacing is 10 meters. Four types of strata and three reflection interfaces are simulated in the model, and the thickness of each stratum is 1000 meters. From top to bottom, the P-wave velocities are 1800m / s, 2000m / s, 2200m / s and 2400m / s, and the S-wave velocities are 1000m / s, 1100m / s, 1200m / s and 1300m / s.

[0085] After the forward modeling, the model data is processed. Before the second interferometry operation, the longitudinal and transverse wave fields are separated. Since the direct wave is no longer needed in this step, the direct wave also needs to be removed. After the preliminary preprocessing, the PP wave and PS wave required for the calculation are obtained, such as Fig.11 shown.

[0086] After the data has been preprocessed, the second interferometric calculation begins. Different shot points and detector points are selected in turn, and the correlation calculation is performed in two steps. Finally, Fig.12 The SS wave virtual source record is shown. This record can be considered as the case where a shear wave source is used for excitation and the detector receives the shear wave. During the calculation process, due to the influence of the ray path, the generated virtual source record is limited, and only the virtual source record of the intermediate detector data can be obtained, which is basically consistent with the theory.

[0087] Fig.12The reflection time of the middle channel is 1.97s, 3.78s and 5.42s respectively. According to the velocity and depth in the model, the actual SS wave propagation time is calculated to be 2s, 3.81s and 5.47s. After comparison, it can be seen that the maximum time difference between the two does not exceed 0.05s, and the result is relatively accurate. Then select the appropriate detector range to complete the calculation of the remaining detector receiving data. Finally, the virtual source SS wave record is used for conventional processing to obtain the superposition profile of the virtual source data. Fig.13 As shown in the figure, the structure in the profile is basically consistent with the strata in the model, the event axis is horizontal, and the depth corresponding to each reflection axis is obtained by calculating the propagation time, which is also basically consistent with the model. Therefore, it can be seen that the principle of the second step of seismic interferometry is basically established.

[0088] Based on the demonstration of the above two model results, it can be seen that the PS wave interferometry proposed this time is basically valid and can be applied to the data processing of OBN or high-density OBS exploration. Using this method, not only the influence of the water layer is eliminated, but also the data of the X and Z components are applied, and finally the SS wave information of the area can be quickly obtained, providing a reference for the subsequent fine processing and interpretation.

[0089] Embodiment 4:

[0090] Based on the model data, the method proposed in the present invention is applied to the measured OBN data. One shot line and one receiving line are selected for processing. There are 314 shots in the shot line, with an average shot spacing of 32.4 meters. There are 225 detectors in the receiving line, with an average spacing of 45.2 meters. The X component and Z component are mainly used in data processing. In the original record, the refracted wave energy is too strong, so the refracted wave part in the record is first cut off. After cutting off, the record is as follows: Fig.14 and 15 Then the data is separated into longitudinal and transverse waves to obtain PP waves and PS waves, as shown in Fig.16 , 17 As shown, the separated data are used in the data processing of the present method.

[0091] First, the direct wave is picked up, and the direct wave and the separated PP wave and PS wave are processed by seismic interferometry to obtain the virtual source record where all the shot check points are located on the seabed after the first operation. Fig.18 , 19 shown.

[0092] Then, according to the model data processing flow, the virtual source record obtained in the previous step is operated for the second time to obtain the virtual source SS wave seismic record. Fig. 20 shown.

[0093] Compared with the model data, the wave field is more complex in the processing of actual data, so the signal-to-noise ratio in the obtained results is relatively low. In general, this method can be applied to the data processing of marine OBN or intensive OBS exploration.

[0094] It can be understood that the method mentioned in the present invention uses two types of data, the X component and the Z component, during processing. The X component mainly represents the shear wave information of the stratum, so compared with the existing method, the shear wave field is clearer and the processing result is more accurate. The method proposed in the present invention further improves the utilization rate of data and can obtain more underground structure information.

[0095] It can be understood that when processing data, in the virtual source records obtained by using this method, the shot check points are all located at the seabed, eliminating the influence of the seawater layer, and can be processed using conventional land seismic exploration data processing methods. At the same time, compared with conventional PS wave data processing, the virtual source record obtained by this method is an SS wave record, which indicates the situation where the shear wave source excites the shear wave reception, so the PP wave data processing method can be directly used for processing and imaging. After processing, the obtained virtual source record can be directly used to obtain the shear wave velocity of the work area using the velocity analysis method, which saves a lot of time compared with conventional PS wave data processing. When processing PS wave data conventionally, it is necessary to repeatedly iterate the position of the common conversion point, and continuously update the iterative PS wave velocity through the PP wave velocity in the area, which is relatively time-consuming and has a huge workload. Using this method for processing, the shear wave velocity of the work area can be obtained simply and quickly, and the shear wave profile of the work area can be obtained at the same time, which can provide a reference for subsequent refined processing.

[0096] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

[0097] Many other changes and modifications may be made without departing from the concept and scope of the present invention.It should be understood that the present invention is not limited to the specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for converting shear wave data of OBN or OBS exploration based on seismic interferometry, characterized in that: The method comprises: S1: Separate the P-wave and S-wave fields of the collected original X-component and Z-component seismic data to obtain PP waves and PS waves; S2: Select sea surface shot points and seabed geophones, use seismic interferometry to perform cross-correlation operations on the direct waves, PP waves and PS waves received by the seabed geophones, and obtain virtual source PP wave and PS wave records when the shot points are all located on the seabed; S3: Based on the virtual source record of the gun check point located on the seabed, the reflected wave is processed by the second interference method, PP+PS=SS, that is, the virtual source record of the SS wave is obtained by combining the PP wave and the PS wave. Then, the conventional longitudinal wave data processing method is used to finally obtain the profile of the virtual source SS wave.

2. The method for converting shear wave data of OBN or OBS exploration based on seismic interferometry according to claim 1, characterized in that: The step S2 specifically includes: Perform cross-correlation operation on the xAOB and yOB data to eliminate the time of the seismic wave propagation path in the water, and finally obtain the seismic record with A as the virtual source and B as the receiver; The principle of the method is shown in the following formula: Among them, x and y are the shot points on the water surface, and A and B are the detectors on the seabed.

3. The method for converting shear wave data of OBN or OBS exploration based on seismic interferometry according to claim 1, characterized in that: The step S3 specifically includes: Step 1: Perform interference processing on the two data of AOB and AON. After cross-correlation operation, eliminate the incident wave part AO and obtain BN; Step 2: In the first step, N is the record of the virtual source point. Then, N is taken as the shot point, and M is the PS wave NM received by the detector. BN and NM are cross-correlated, and the common path NO is eliminated. Finally, BM is obtained. This result can be regarded as B is the virtual source point and M is the virtual source record of the detector. In the record, point B is the shear wave source excitation, and point M is the received SS wave signal; the principle formula of the method is as follows: ω ψS (t,M,B)=∫∫[ω PS (t,A,B)*ω PS (t,N,M)*ω PP (-t,A,N)]dAdN (2) Among them, M and N are both seabed detectors.

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