A method for base surface correction of seismic reflection data acquired with vertical cables
By employing Radon transform and towed cable data processing techniques, the problems of high computational load and imaging difficulties in datum plane correction during vertical cable acquisition data processing were solved, achieving efficient data correction and imaging results.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- QINGDAO INST OF MARINE GEOLOGY
- Filing Date
- 2023-10-31
- Publication Date
- 2026-06-16
Smart Images
Figure CN117518247B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of seismic exploration data processing, and specifically relates to a reference plane correction technology for seismic reflection data acquired by vertical cable acquisition. Background Technology
[0002] Vertical cable acquisition is a marine three-dimensional exploration technique that involves vertically deploying a multi-node hydrophone array in the water to record the reflected seismic wave field excited by an air gun source. Compared with conventional towed cable acquisition, this method is less affected by waves and merchant ships, has stronger obstacle avoidance capabilities, and the acquired seismic signals have advantages such as high signal-to-noise ratio, rich low-frequency components, wide azimuth angle, high coverage, and high imaging accuracy for key target areas, especially suitable for imaging complex geological structures.
[0003] Vertical cable seismic exploration technology was first developed by the US Navy for anti-submarine warfare using walkaway vertical seismic profiling (WVSP). The processing technology based on towed cable acquisition data cannot be directly applied to the processing of vertical cable acquisition data, so special data processing technology is required.
[0004] Currently, the method of variable depth wavefield extrapolation is used for reference plane correction in the processing of vertical cable acquisition data both domestically and internationally. This involves extrapolating the detectors at different depths along different paths and at different distances, and using different extrapolation operators. This method involves a large amount of computation and requires high accuracy of the extrapolation operators. It is also very easy to damage the amplitude and phase characteristics of the wavefield, affecting the correct imaging of the vertical cable acquisition data. Summary of the Invention
[0005] This invention addresses the shortcomings of existing technologies in the process of extrapolating variable depth wavefields for reference plane correction in vertical cable data processing, such as large computational load and difficulty in accurate imaging. It proposes a reference plane correction method for vertical cable seismic reflection data, which corrects the receiver points to the same reference plane as the shot points, and then uses towed cable data processing technology to accurately image the underground structures detected by the data.
[0006] This invention is achieved using the following technical solution: a method for correcting the reference surface of seismic reflection data acquired by a vertical cable, comprising the following steps:
[0007] Step A: First, separate the uplink and downlink waves in the vertical cable data;
[0008] The uplink and downlink wave separation technique based on Radon transform is used to transform seismic data from the time domain to the τ-p domain, and the uplink and downlink waves are separated in the τ-p domain. The basic principle is as follows:
[0009] The data is viewed as a two-dimensional array of τ and p. For each point in the data, there is a slope p. A set of diagonal lines is taken and scanned from 0° to 90°. The data on the diagonal lines are then superimposed and mapped to the corresponding position of τ-p. This process is repeated for all sample points to achieve the linear Radon forward transform of the data.
[0010] Then, based on the difference between the uplink and downlink waves of the vertical cable in the τ-p domain, they are separated. Then, the data is converted into the spatiotemporal domain through the linear Radon inverse transform, and finally the uplink and downlink waves of the vertical cable data are separated.
[0011] Step B: Then, for the upflow wave data, using the seabed as the reference plane, the receiver points are corrected to the same reference plane as the shot points, and the coordinates of the receiver points are also corrected to the corresponding positions, so that the corrected data is similar to the towed cable data.
[0012] We will discuss two scenarios:
[0013] (1) Assuming the strata are flat, and taking the seabed as the reference surface, calculate the correction time t0;
[0014] (2) Assuming that the strata have a certain dip angle, the correction time t1 is calculated with the seabed as the reference surface;
[0015] Then, the influence of seabed dip on correction time is analyzed, and the applicability of the two cases is analyzed through model data. Using the correction time, the geophone is aligned to the same plane as the shot point, and the coordinates of the geophone are also aligned to the corresponding position.
[0016] Step C: Finally, the data acquisition data of the vertical cable is processed using towed seismic data processing technology to achieve correct imaging of the vertical cable acquisition data.
[0017] Furthermore, in step B, assuming the seabed strata are flat, let the horizontal distance between the shot receiver and the receiver be x, the immersion depth of the geophone be h, the water velocity be V1, the water depth be H1, and the incident angle of the wave propagating to the seabed be θ1, and calculate the correction time t0:
[0018]
[0019] Therefore, it is found that when the seabed dip angle is zero, the correction time is related to the horizontal distance of the shot receiver, the depth of the geophone, and the depth of the seabed.
[0020] Furthermore, in step B, assuming a certain angle exists in the seabed strata, let the horizontal distance between the shot receiver and the receiver be x, the immersion depth of the geophone be h, the water velocity be V1, the water depth be H1, the incident angle of the wave propagating to the seabed be θ1, and the seabed dip angle be θ0. Then, the correction time t1 is calculated using the following formula:
[0021]
[0022] Therefore, the calibration time is related to the detector's immersion depth, seabed depth, incident angle, and seabed inclination. When the detector's immersion depth, seabed depth, and incident angle are determined, the calibration time is related to the seabed inclination.
[0023] Furthermore, in step B, the detector point is aligned to the same reference plane as the shot point in the following manner:
[0024] (1) Analyze the influence of seabed inclination on correction time by establishing a model: Set the model and parameters according to the acquisition characteristics of the vertical cable. The parameters include, but are not limited to, shot point position, shot spacing, maximum and minimum shot-receiver distance, cable position, number of detectors, and detector placement depth. Through modeling analysis, it is determined that when the seabed inclination is less than or equal to 20°, the correction time is determined by the calculation formula of t0, and when the seabed inclination is greater than 20°, the correction time is determined by the calculation formula of t1.
[0025] (2) Based on the calculated correction time, a zero correction baseline for static correction is formed, and each channel is directly aligned with this baseline to achieve the purpose of correcting the reference surface of the seismic reflection data acquired by the vertical cable.
[0026] Furthermore, in step C, the three-dimensional towed seismic data processing technology includes, but is not limited to, multiple wave suppression technology, stacking, and migration imaging. After the reference plane is corrected, the position of the receiver points is not uniform. The three-dimensional observation technology of the towed cable is used to perform three-dimensional observation on the corrected data, and then the data after observation is processed by the three-dimensional towed seismic data processing technology.
[0027] Compared with the prior art, the advantages and positive effects of the present invention are as follows:
[0028] Based on the characteristics of vertical cable seismic data, this scheme designs a data reference plane correction technique suitable for this type of seismic data. Reference plane correction aligns the position of the receiver points to the same reference plane as the shot points, which is beneficial for subsequent noise suppression, multiple suppression, and migration imaging. This overcomes the limitations in the data processing of this seismic data and ultimately achieves accurate imaging. Simultaneously, the influence of stratigraphic dip angle, receiver immersion depth, and seawater depth on imaging quality is analyzed to determine the applicable scope and optimal acquisition parameters of this method, demonstrating high practical application and promotion value. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the reference surface calibration method according to an embodiment of the present invention;
[0030] Figure 2This is a schematic diagram of vertical cable data collected in an embodiment of the present invention, wherein (a) is a single shot record of the vertical cable, (b) is an uplink record after uplink and downlink wave separation, and (c) is a downlink record after uplink and downlink wave separation;
[0031] Figure 3 This is a schematic diagram of vertical cable observation when the seabed inclination angle is zero, according to an embodiment of the present invention.
[0032] Figure 4 This is a schematic diagram of vertical cable observation when the seabed inclination angle is θ0 according to an embodiment of the present invention;
[0033] Figure 5 The following are schematic diagrams of the model and parameter settings in an embodiment of the present invention: (a) is a schematic diagram of the model; (b) shows the relationship between the correction time and the incident angle when the detector depth is 400 meters; (c) shows the relationship between the correction time and the incident angle when the detector depth is 6.25 meters; (d) shows the relationship between the difference between the detector depth of 6.25 meters and the seabed inclination angle of zero and the incident angle; and (e) shows the relationship between the difference between the detector depth of 400 meters and the seabed inclination angle of zero and the incident angle.
[0034] Figure 6 This is a schematic diagram of the shot gathering record before and after the reference plane correction in an embodiment of the present invention, wherein (a) is the shot gathering record before the reference plane correction, and (b) is the shot gathering record after the reference plane correction;
[0035] Figure 7 This is a schematic diagram of the shot gather record before and after multiple wave suppression in an embodiment of the present invention, wherein (a) is the shot gather record before multiple wave suppression; and (b) is the shot gather record after multiple wave suppression.
[0036] Figure 8 This is a superimposed cross-section of multiple waves after three-dimensional observation and suppression, according to an embodiment of the present invention. Detailed Implementation
[0037] To better understand the above-described objects, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may be practiced in other ways than those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.
[0038] This embodiment discloses a method for correcting the reference surface of seismic reflection data acquired by a vertical cable, such as... Figure 1 As shown, it includes the following steps:
[0039] Step A: Separate uplink and downlink waves from the vertical cable data. Specifically, uplink and downlink wave separation technology based on Radon transform can be used to convert the seismic data from the time domain to the τ-p domain, and then separate the uplink and downlink waves in the τ-p domain.
[0040] Step B: For the upflow wave data, using the seabed as the reference plane, calibrate the geophone points to the same reference plane as the shot points, and at the same time, calibrate the coordinates of the geophone points to the corresponding positions.
[0041] Two cases are discussed: (1) Assuming the strata are relatively flat, the seabed is used as the reference surface to calculate the correction time; (2) Assuming the strata have a certain dip angle, the seabed is used as the reference surface to calculate the correction time; then the influence of the seabed dip angle on the correction time is analyzed and the applicable range of the two cases is analyzed through model data; using the correction time, the geophone point is corrected to the same surface as the shot point, and the coordinates of the geophone point are also corrected to the corresponding position.
[0042] Step C: Process the vertical cable acquisition data using towed seismic data processing technology to achieve accurate imaging of the vertical cable acquisition data.
[0043] Specifically, in order to better understand the present invention, the following detailed description is provided:
[0044] Step A: The uplink / downlink separation technique based on Radon transform uses a linear Radon transform. Below is the linear Radon positive transform U(τ,p):
[0045]
[0046] Where u(t, x) represents the spatiotemporal domain data, x represents the data location, τ represents the intercept time, and p represents the slowness. The data is viewed as a two-dimensional array of τ and p. For each data point, there is a slope p. A set of slopes is taken, scanning from 0° to 90°. The data on these slopes are then superimposed and mapped to the corresponding positions in τ-p. This process is repeated until all samples are collected, thus achieving the linear Radon forward transform of the data. Then, the uplink and downlink waves of the vertical cable are separated based on their differences in the τ-p domain. Finally, the data is converted to the spatiotemporal domain using a linear Radon inverse transform, ultimately achieving the separation of the uplink and downlink waves of the vertical cable data. Specifically, as follows... Figure 2 As shown.
[0047] Below is the formula for the linear Radon inverse transform:
[0048]
[0049] In step B, the correction time is assumed to be t0 when the strata are flat, and t1 when the seafloor strata have a certain angle. The specific calculation process is as follows:
[0050] (1) When the seabed strata are relatively flat, it is assumed to be a flat stratum. See details. Figure 3Where the horizontal distance between the shot and receiver is x, the immersion depth of the geophone is h, the water velocity is V1, the water depth is H1, and the angle of incidence of the wave propagating to the seabed is θ1, the correction time t0 can be calculated:
[0051]
[0052] in
[0053]
[0054] From formula (4), we can obtain
[0055]
[0056] Substituting formula (5) into formula (3), we get
[0057]
[0058] The correction time when the strata are relatively flat can be calculated from equation (6). It can be seen from equation (6) that when the seabed dip angle is zero, the correction time is related to the horizontal distance of the shot receiver, the sinking depth of the receiver and the depth of the seabed.
[0059] (2) When the seafloor strata have a certain angle, see details. Figure 4 The horizontal distance between the shot and receiver is x, the immersion depth of the geophone is h, the water velocity is V1, the water depth is H1, the angle of incidence of the wave reaching the seabed is θ1, and the seabed dip angle is θ0. The dip angle ∠R1RR0=θ1+θ0 can be calculated, thus yielding the correction time t1.
[0060]
[0061] according to Figure 4 The schematic diagram of vertical cable observation allows for the calculation of ∠FSM=θ1-θ0, and thus the calculation of...
[0062] FM=H1*tan (θ1-θ0) (8)
[0063] MD=x-FM=x-H1*tan (θ1-θ0) (9)
[0064]
[0065] Substituting formulas (8) and (9) into formula (10) yields...
[0066]
[0067] Therefore, calculate
[0068]
[0069] Substituting formula (11) into formula (7) yields...
[0070]
[0071] As can be seen from equation (12), the calibration time is related to the depth of the detector, the depth of the seabed, the incident angle, and the seabed inclination. When the depth of the detector, the depth of the seabed, and the incident angle are determined, the calibration time is related to the seabed inclination.
[0072] It can be seen that when the seabed has a dip angle, the correction time is related to the seabed dip angle. However, in actual data processing, it is difficult to determine the seabed dip angle, and the seabed dip angle is different at each point. The following section uses a model to analyze the impact of seabed dip angle on the correction time.
[0073] Based on the acquisition characteristics of the vertical cable, the model and parameters are set, see [link / reference]. Figure 5 (a) shows the red inverted triangles indicating the shot locations, with a total of 41 shots. The shot spacing is 25 meters, the minimum shot-to-detector distance is 0 meters, and the maximum shot-to-detector distance is 500 meters. The black vertical lines indicate the cable locations, with detectors spaced 6.25 meters apart, totaling 64 detectors. The deepest detector is submerged at a depth of h. m =400 meters, the minimum seabed depth is 500 meters, the maximum seabed depth is 536 meters, the water velocity is V1 = 1500 meters / second, the seabed dip angle is θ0, and the incident angle is θ1.
[0074] pass Figure 3 The schematic diagram shows that the incident angle θ1 satisfies the following relationship:
[0075] H1tanθ1+(H1-h)tanθ1=x (13)
[0076]
[0077] Where x is the horizontal distance between the shot and receiver, H1 is the seabed depth, and h is the depth at which the geophone is submerged. Based on the model parameters, the maximum incident angle θ can be calculated. 1max for
[0078]
[0079] Where x m It is the horizontal distance of the maximum shot-receiver point, h m The maximum depth for the geophone placement is given. Therefore, based on the model parameters, the maximum incident angle can be calculated to be 39.8034°. The following analysis examines the correction time difference for the vertical cable data. From formula (7), it can be seen that the correction time differs for different geophone points, different incident angles, and different seabed inclination angles, as follows:
[0080]
[0081] When the detector's immersion depth is determined, calculate the curve of calibration time versus incident angle for different seabed inclination angles (different colors represent different seabed inclination angles), see... Figure 5 (b) and Figure 5 (c) represents the cases when the detector is submerged at depths of 6.25 meters and 400 meters, respectively. It can be seen that when the detector submersion depth is fixed, the smaller the seabed inclination angle, the smaller the incident angle, the smaller the correction time, and the smaller the difference in correction time; conversely, the larger the inclination angle, the greater the difference. The correction time for different seabed inclination angles is then subtracted from the correction time when the seabed inclination angle is zero, yielding a curve showing the difference as a function of the incident angle. Figure 5 (d) and Figure 5 (e) shows the curves of the difference between the detector's immersion depth and the zero offset correction time as a function of the incident angle when the detector is immersed at a depth of 6.25 meters and 400 meters. As can be seen from the figure, the smaller the immersion depth of the detector, the smaller the difference between the detector and the zero seabed inclination angle, and vice versa. See Table 1 and Table 2 for details.
[0082] Table 1 shows the difference between the current value and the value when the seabed dip angle is zero (detector depth is 6.25 meters).
[0083]
[0084] Table 2 shows the difference between the current value and the value when the seabed dip angle is zero (detector depth is 400 meters).
[0085]
[0086] The difference is largest at a depth of 6.25 meters, a seabed inclination of 20°, and an incident angle of 39°, reaching 0.0027. The difference is also largest at a depth of 400 meters, a seabed inclination of 20°, and an incident angle of 39°, reaching 0.1746. Furthermore, the smaller the depth of the geophone, the smaller the difference. This indicates that when the seabed is relatively flat (i.e., the seabed inclination is less than or equal to 20°) and shallow, the correction time in step A1 can be used, resulting in a small error and simple calculation, without requiring calculation of the inclination at every point on the seabed. However, when the seabed inclination is greater than 20°, the correction time in step A2 is used. This correction time requires calculation of the seabed inclination, thus necessitating a more precise seabed time. If conditions permit, multibeam bath data can be used to obtain a precise seabed time, and then the seabed inclination at each point can be further calculated to obtain the final correction time.
[0087] Then, using the determined correction time mentioned above, a zero-correction baseline for static correction is formed. Each channel is directly aligned with this baseline, achieving the purpose of calibrating the reference plane for seismic reflection data acquired by the vertical cable. This means calibrating the geophone to the same reference plane as the shot point, and simultaneously calibrating the coordinates of the geophone point to the corresponding position, facilitating the subsequent observation of the vertical cable data. Specifically, as follows... Figure 6 and Figure 7 As shown.
[0088] Finally, in step D, after the reference plane is corrected, the positions of the receiver points are not uniform. Therefore, it is necessary to use a towed cable three-dimensional observation technique to perform three-dimensional observation of the corrected data, such as... Figure 8 As shown, the data after stabilization can be processed using mature 3D towed seismic data processing techniques, such as multiple suppression, stacking, and migration imaging.
[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A method for base surface correction of seismic reflection data acquired with vertical cables, characterized by, Includes the following steps: Step A: Separate uplink and downlink waves from the vertical cable data; Step B: For the upflow wave data, using the seabed as the reference plane, calibrate the geophone points to the same reference plane as the shot points, and at the same time, calibrate the coordinates of the geophone points to the corresponding positions. Step C: Process the vertical cable acquisition data using towed seismic data processing technology to achieve accurate imaging of the vertical cable acquisition data; Step B involves two scenarios: (1) Assuming the strata are flat, calculate the correction time with the sea floor as the reference surface ; (2) Assuming the existence of dip angle, calculate the correction time with the sea floor as the reference surface ; Then, the influence of seabed dip on correction time is analyzed, and the applicability of the two cases is analyzed through model data. Using the correction time, the geophone is aligned to the same plane as the shot point, and the coordinates of the geophone are also aligned to the corresponding position. In step B, assuming the seabed strata are flat, the horizontal distance between the shot receiver points is set as follows: The detector's immersion depth is The water velocity is The water depth is The angle of incidence of the wave as it propagates to the seabed is Calculate the correction time : Therefore, it can be concluded that when the seabed dip angle is zero, the correction time is related to the horizontal distance of the shot receiver, the depth of the geophone, and the depth of the seabed. In step B, assuming an angle exists in the seabed strata, the horizontal distance between the shot receiver and the receiver is set as follows: The detector's immersion depth is The water velocity is The water depth is The angle of incidence of the wave as it propagates to the seabed is The seabed dip angle is Then the correction time Calculated using the following formula: Therefore, the calibration time is related to the detector's immersion depth, seabed depth, incident angle, and seabed inclination. When the detector's immersion depth, seabed depth, and incident angle are determined, the calibration time is related to the seabed inclination.
2. The method for correcting the reference surface of seismic reflection data acquired by a vertical cable according to claim 1, characterized in that: In step A, uplink and downlink wave separation technology based on Radon transform is used to convert the seismic data from the time domain to the uplink / downlink domain. Domain, in The principle of separating uplink and downlink waves in the domain is as follows: View the data as a... and A two-dimensional array, with a slope for each point in the data. Take a set of diagonal lines, starting from 0 ° To 90 ° Perform a scan, then overlay the data on the diagonal lines, and then map it to... At the corresponding locations, repeat the process for all sample points to achieve a linear Radon transform for the data. Then, based on the uplink and downlink waves of the vertical cable... The differences in the domain are separated, and the data is then transformed into the spatiotemporal domain through linear Radon inverse transform, ultimately achieving the separation of uplink and downlink waves in vertical cable data.
3. The method for correcting the reference surface of seismic reflection data acquired by a vertical cable according to claim 1, characterized in that: In step B, the geophone point is aligned to the same reference plane as the shot point in the following manner: (1) Analyze the influence of seabed dip angle on correction time by establishing a model: Set the model and parameters according to the acquisition characteristics of the vertical cable. The parameters include the shot point location, shot spacing, maximum and minimum shot-receiver distance, cable location, number of geophones, and geophone immersion depth. Through modeling analysis, it is determined that when the seabed dip angle is less than or equal to 20°, the correct time is 100°. The calculation formula determines the correction time. When the seabed inclination angle is greater than 20°, the following method is used. The calculation formula determines the correction time; (2) Based on the calculated correction time, a zero correction baseline for static correction is formed, and each channel is directly aligned with this baseline, thereby achieving the purpose of correcting the reference surface of the seismic reflection data acquired by the vertical cable.
4. The method for correcting the reference surface of seismic reflection data acquired by a vertical cable according to claim 1, characterized in that: In step C, after the reference plane is corrected, the positions of the receiver points are not uniform. The corrected data is subjected to three-dimensional observation using towed cable seismic data technology. Then, the observed data is processed using three-dimensional towed cable seismic data processing technology.
5. The method for correcting the reference surface of seismic reflection data acquired by a vertical cable according to claim 4, characterized in that: In step C, the three-dimensional towed seismic data processing technology includes multiple wave suppression, stacking, and migration imaging.