Minimum offset and delay calculation method based on direct wave and seabed reflected wave

Abstract

This invention belongs to the field of seismic exploration, specifically relating to a method for calculating minimum offset and delay based on direct waves and seafloor reflected waves. The method includes: selecting single-shot seismic data from a flat seafloor location, picking the direct wave travel time, and picking the seafloor reflected travel time of the first data trace at the single-shot location; performing regression fitting on the picked direct wave travel time to fit the direct wave equation, and obtaining the seawater velocity and initial minimum offset based on the direct wave equation; setting an initial delay time range, and calculating the seafloor depth h for each seismic trace at different delay times based on the seawater velocity, initial minimum offset, and seafloor reflected travel time; calculating the 2h variance based on the seafloor depth of the seismic trace, and obtaining the minimum offset and delay time. This invention can quickly obtain the minimum offset and delay time, achieving accurate positioning of seismic data, and the method is simple and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of seismic exploration, specifically relating to a method for calculating the minimum offset and delay based on direct waves and seabed reflected waves. Background Technology

[0002] Before processing conventional 2D or 3D seismic data, it is necessary to define the observation system, i.e., the spatial relationship between the excitation and receiver points. A correct observation system definition is fundamental to seismic data processing; otherwise, it will directly affect the accuracy and effectiveness of the processing. However, when precise GPS positioning information is lacking, making it difficult to obtain accurate shot-receiver point locations, or when the recording delay of the seismic data acquisition system is uncertain, it is impossible to accurately load the observation system onto the data. The existence of recording delay causes discrepancies between the seafloor reflection time and the actual time, and the minimum offset is inaccurate, preventing the seafloor reflection from being leveled by water velocity. To address these situations, it is usually assumed that the seafloor dip angle is small and the ray propagation follows the common midpoint assumption. However, this assumption is limited in practical applications, resulting in significant positional deviations in calculations. Furthermore, when the recording delay of the seismic data acquisition system is also inaccurate, it severely affects the application of subsequent processing methods such as multiple suppression and the accurate imaging of the data. Summary of the Invention

[0003] This invention overcomes the above-mentioned defects and provides a method for calculating the minimum offset and delay based on direct waves and seabed reflected waves. It solves the problems in the prior art, such as inaccurate shot receiver location due to lack of accurate GPS positioning, uncertain recording delay, distortion of seabed reflection time, and inaccurate loading of the observation system.

[0004] To achieve the above objectives, the method for calculating the minimum offset and delay based on direct waves and seabed reflected waves of the present invention includes the following steps:

[0005] S1. Select single-shot seismic data from flat seabed areas, pick the direct wave travel time, and pick the seabed reflection travel time of the first data at the location of the single shot.

[0006] S2. Perform regression fitting on the direct wave equation to obtain the picked-up direct wave travel time, and obtain the seawater velocity and initial minimum offset based on the direct wave equation.

[0007] S3. Set the initial delay time range, and calculate the seabed depth h of each seismic trace under different delay times based on seawater velocity, initial minimum offset distance, and seabed reflection travel time.

[0008] S4. Calculate the 2-hour variance based on the seabed depth of the seismic channel to obtain the minimum offset distance and delay time.

[0009] Furthermore, step S2 is implemented as follows:

[0010] S21 assigns an offset value to each seismic trace based on the single-shot data of the acquired direct wave travel time. The offset distance is: ,in, For lane spacing;

[0011] S22 calculates the mean values ​​of the travel time and offset distance of the direct wave, respectively.

[0012] Mean travel time for direct waves: ;

[0013] Mean offset distance: ;

[0014] S23 calculates the autocorrelation coefficient between the travel time and offset of the direct wave, measuring the strength and direction of their linear relationship, as follows:

[0015] ,

[0016] in, The range of values ​​is ,like A value close to +1 indicates a strong positive linear relationship. A value close to -1 indicates a strong negative linear relationship. A value close to 0 indicates a lack of linear correlation;

[0017] If a linear relationship exists for S24, the equation coefficients are calculated using linear fitting based on the direct wave time-distance curve to obtain the seawater velocity. and initial minimum offset The direct wave time-distance curve is represented as follows:

[0018] ,

[0019] in, Indicates the number of shots recorded in a single shot. road, For lane spacing, It is the first Road offset, Indicates the first The propagation time of a direct wave. Indicates the speed of seawater.

[0020] Furthermore, in step S3, the initial delay time range is set to... Based on the earthquake propagation path, the formula for the seafloor depth h of each earthquake under different delay times is:

[0021] ,

[0022] in, The depth of the seabed For the speed of seawater, For the propagation time of seismic waves, The offset distance is given by the following formula:

[0023] ,

[0024] ,

[0025] in, During the journey to retrieve seabed reflections, This is the delay time.

[0026] Furthermore, in step S4, The variance is expressed as:

[0027] ,

[0028] Where N represents the number of seismic traces;

[0029] The distribution of variance values ​​for each seismic trace is statistically analyzed, and the delay time and minimum offset corresponding to the minimum variance are the desired results.

[0030] Furthermore, the minimum offset is .

[0031] Furthermore, if the calculated delay time is ±250ms, it indicates that the delay time is too large, and the initial delay time range needs to be increased before recalculation.

[0032] Compared with the prior art, the advantages of the present invention are as follows:

[0033] This invention, conducted in the artillery zone, proposes a method for calculating the minimum offset and delay based on the propagation path of seismic waves and the reflection of the seabed. This method can accurately calculate the minimum offset and recording delay without considering the travel time of first-order multiple waves, thereby enabling accurate data localization. It solves the problem of missing minimum offset and recording delay information in acquired data and achieves accurate positioning of seismic data. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method for calculating the minimum offset and delay based on direct waves and seabed reflected waves in this invention.

[0035] Figure 2 This is a diagram illustrating the shot point, receiver point, and seismic wave propagation principle in an embodiment of the present invention.

[0036] Figure 3 This is a schematic diagram of a known single-shot recording according to an embodiment of the present invention;

[0037] Figure 4 This is a fitted curve of the travel time versus offset of a direct wave recorded by a known single shot in an embodiment of the present invention;

[0038] Figure 5 This is a schematic diagram of the seabed leveling of the shot collection in a known single-shot record definition observation system according to an embodiment of the present invention;

[0039] Figure 6 This is a schematic diagram of a single-shot record based on actual data from an embodiment of the present invention;

[0040] Figure 7 This is a time-lapse diagram of actual data collected from the seabed in an embodiment of the present invention;

[0041] Figure 8 This is a fitted curve of the travel time and offset distance of the direct wave based on actual data from an embodiment of the present invention.

[0042] Figure 9 This is a schematic diagram of the seabed leveling after the observation system is defined based on actual data in an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] This invention primarily addresses the problem of insufficient precise GPS positioning information in acquired data, making it impossible to obtain accurate shot-receiver point locations, or the inability to determine accurate seafloor reflection times when the recording delay of the seismic data acquisition system is uncertain, thus hindering accurate loading of seismic data into observation systems. It proposes a method for calculating the minimum offset and delay based on direct waves and seafloor reflected waves. This invention is performed within the shot area, using the travel time of a single shot's direct wave, seafloor reflections in relatively flat terrain, and track spacing, to fit and calculate the minimum offset and delay time using the direct wave travel time curve and the reflected wave travel time curve. This allows for rapid determination of the minimum offset and delay time, achieving accurate positioning of seismic data. The method is simple and easy to implement. Figure 1 As shown, the details are as follows:

[0046] S1 selects single-shot seismic data from areas with flat seabed terrain, picks the direct wave travel time, and picks the seabed reflection travel time of the first data from the location of the single shot.

[0047] Since direct waves propagate more stably and are easier to identify in areas with relatively flat seabed terrain, we selected single-shot data from areas with relatively flat seabed terrain and manually picked up their direct wave travel time. At the same time, we manually picked up the seabed reflection travel time of a segment of the first data from the location of that single shot.

[0048] S2 performs regression fitting on the picked-up direct wave travel time and offset to obtain the direct wave equation, and obtains the seawater velocity and initial minimum offset based on the direct wave equation.

[0049] The direct wave time-distance curve is represented as follows: ,

[0050] in, Indicates the number of shots recorded in a single shot. road, For lane spacing, It is the first Road offset, Indicates the first The propagation time of a direct wave. Indicates the speed of seawater.

[0051] Using the direct wave travel time curve, regression fitting is performed on the picked direct wave travel time to obtain the regression-fitted direct wave equation, where the slope is... Represents the velocity of seawater, intercept This represents the initial minimum offset. Due to issues such as inertia, dispersion, and attenuation absorption during seismic wave propagation, the sound wave velocity is low when the offset is small, and the waveform is stretched and distorted due to the frequency drop when the offset is large, resulting in a shorter pickup reflection time and increased calculation speed. Therefore, in calculations, the offset data of the middle range is generally selected, as the seismic wave velocity and waveform are relatively stable within this range. The specific calculation process is as follows:

[0052] (1) For the single-shot data with the picked direct wave travel time, assign a value to the offset of each seismic trace, the first... The offset distance is: ,in, For lane spacing;

[0053] (2) Calculate the mean values ​​of the travel time and offset distance of the direct wave, respectively.

[0054] Mean travel time for direct waves: ;

[0055] Mean offset distance: ;

[0056] (3) Using the travel time and offset data of the direct wave, calculate the autocorrelation coefficient between them to measure the strength and direction of their linear relationship. The calculation is as follows:

[0057] ,

[0058] in, The range of values ​​is ,like A value close to +1 indicates a strong positive linear relationship between the two variables. A value close to -1 indicates a strong negative linear relationship between the two variables. A value close to 0 indicates a lack of linear correlation;

[0059] (4) If a linear relationship exists, the seawater velocity is obtained by linearly fitting the equation coefficients of the direct wave travel time curve based on the direct wave travel time data and the corresponding offset data. and initial minimum offset .

[0060] S3 sets the initial delay time range and calculates the seabed depth h of each seismic trace at different delay times based on seawater velocity, initial minimum offset distance, and seabed reflection travel time.

[0061] If the data record has no delay (i.e., the delay is 0), then the initial minimum offset is the actual minimum offset; if the data record has a delay... First, set the initial delay time range as follows: According to the propagation path of seismic waves ( Figure 2 The formula for the seafloor depth h for each earthquake under different delay times is:

[0062] ,

[0063] in, Indicates the depth of the seabed. For the speed of seawater, For the propagation time of seismic waves, The offset distance is given by the following formula:

[0064] ,

[0065] ,

[0066] in, During the journey to retrieve seabed reflections, For delay time;

[0067] S4 calculates seabed depth based on seismic traces. The variance is used to obtain the minimum offset and delay time;

[0068] After obtaining the depth of each seismic trace, calculate... The variance is expressed by the formula:

[0069] ,

[0070] Where N represents the number of seismic traces, Indicates seabed depth;

[0071] Finally, the distribution of variance values ​​for each seismic trace is statistically analyzed, and the delay time corresponding to the minimum variance is determined. With minimum offset This is the desired result. If the calculated optimal delay time is ±250ms, it indicates that the delay time is too large, and the initial delay time range needs to be increased and recalculated.

[0072] After calculating the minimum offset and delay time, the observation system is defined to obtain headway data such as offset, seabed reflection time, and CMP. Correctly determined observation data can be dynamically corrected using seawater velocity to level the seabed, and the relationship between the first-order multiple waves and the seabed reflection time (twice the length of the seabed reflection time) can be established, thus facilitating subsequent data processing.

[0073] Example 2:

[0074] Figure 3 This is a single-shot record with known parameters, as shown in Table 1.

[0075] Table 1 Parameter Table

[0076]

[0077] Using this known single-shot record, a time-distance curve is fitted. The fitted curve of the direct wave travel time versus offset in the middle segment is selected as follows: Figure 4 As shown, the initial minimum offset distance and seawater velocity are 142.5m and 1500m / s, respectively, and the initial delay time range is set to... Based on the seabed reflections collected during travel Calculate the seafloor depth (2h) and variance for each seismic trace under different delay times, and obtain the minimum offset and delay time; the delay time corresponding to the minimum variance is also calculated. With minimum offset Compared with Table 1, the minimum offset and delay time calculated by this invention are consistent with the data in the table. After defining the observation system using this data, the shot collection can be leveled using the water velocity. Figure 5 This demonstrates that the method in the embodiments of the present invention is effective.

[0078] Example 3:

[0079] like Figure 6The image shows a single-shot record from actual data. The travel time of the direct wave in a relatively flat area was selected, and a time-distance curve was fitted. The fitted curve of the travel time of the direct wave in the middle segment versus the offset distance is shown below. Figure 8 Thus, the seawater velocity was obtained respectively. Initial minimum offset Meanwhile, during the seabed reflection travel time for picking up the first data of a single gun ( Figure 7 ) The initial delay time range was set to (-250ms, +250ms). Based on the seismic wave propagation path, the seafloor depth of each seismic trace was calculated under different delay times. and calculate The variance is used to obtain the minimum offset distance. , and delay time The correct observation system definition is achieved by utilizing the minimum offset and delay time, such as... Figure 9 As shown, the data obtained after accurate observation can be used to level the seabed by applying dynamic correction based on seawater velocity, proving that the calculations of this invention are effective.

[0080] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for calculating the minimum offset and delay based on direct waves and seabed reflected waves, characterized in that, Includes the following steps: S1. Select single-shot seismic data from flat seabed areas, pick the direct wave travel time, and pick the seabed reflection travel time of the first data at the location of the single shot. S2. Perform regression fitting on the direct wave equation to obtain the picked-up direct wave travel time, and obtain the seawater velocity and initial minimum offset based on the direct wave equation. S3. Set the initial delay time range, and calculate the seabed depth h of each seismic trace under different delay times based on seawater velocity, initial minimum offset distance, and seabed reflection travel time. S4. Calculate the 2-hour variance based on the seabed depth of the seismic channel to obtain the minimum offset distance and delay time.

2. The method for calculating the minimum offset and delay based on direct waves and seabed reflected waves according to claim 1, characterized in that, Step S2 is implemented as follows: S21 assigns an offset value to each seismic trace based on the single-shot data of the acquired direct wave travel time. The offset distance is: ,in, For lane spacing; S22 calculates the mean values ​​of the travel time and offset distance of the direct wave, respectively. Mean travel time for direct waves: ; Mean offset distance: ; S23 calculates the autocorrelation coefficient between the travel time and offset of the direct wave, measuring the strength and direction of their linear relationship, as follows: ， in, The range of values ​​is ,like A value close to +1 indicates a strong positive linear relationship. A value close to -1 indicates a strong negative linear relationship. A value close to 0 indicates a lack of linear correlation; If a linear relationship exists for S24, the equation coefficients are calculated using linear fitting based on the direct wave time-distance curve to obtain the seawater velocity. and initial minimum offset The direct wave time-distance curve is represented as follows: ， in, Indicates the number of shots recorded in a single shot. road, For lane spacing, It is the first Road offset, Indicates the first The propagation time of a direct wave. Indicates the speed of seawater.

3. The method for calculating the minimum offset and delay based on direct waves and seabed reflected waves according to claim 2, characterized in that, In step S3, the initial delay time range is set to... Based on the seismic wave propagation path, the formula for the seafloor depth h of each seismic wave under different delay times is: ， in, Indicates the depth of the seabed. For the speed of seawater, For the propagation time of seismic waves, The offset distance is given by the following formula: ， ， in, During the journey to retrieve seabed reflections, This is a delay time.

4. The method for calculating the minimum offset and delay based on direct waves and seabed reflected waves according to claim 3, characterized in that, In step S4, The variance is expressed as: ， Where N represents the number of seismic traces; Analyze the distribution of variance values ​​for each seismic trace, and determine the time delay corresponding to the minimum variance. The minimum offset distance is the desired result.

5. The method for calculating the minimum offset and delay based on direct waves and seabed reflected waves according to claim 4, characterized in that, Minimum offset distance is .

6. The method for calculating the minimum offset and delay based on direct waves and seabed reflected waves according to claim 4, characterized in that, If the calculated delay time is ±250ms, it indicates that the delay time is too large, and the initial delay time range needs to be increased before recalculation.

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