Undulating surface pre-stack time migration method and undulating surface pre-stack time migration system

Abstract

The invention provides an undulating surface pre-stack time migration method and system, and belongs to the technical field of seismic exploration data processing. The method comprises the following steps: firstly, correcting undulating surface gather data, and correcting a shot point and a detection point of each piece of data to a floating reference surface at a corresponding position; and secondly, respectively calculating travel time from the shot point to the imaging point and travel time from the detection point to the imaging point from the floating reference surfaces of the shot point and the detection point, finally obtaining total travel time of the shot point and the detection point, and completing calculation of a migration imaging result. By using the method, the precision of calculating the travel time of the pre-stack time migration is further improved, efficient and accurate pre-stack time migration processing of a complex earth surface exploration area is realized, the seismic data processing cost is reduced, and the economic benefit is improved.

Description

Technical Field

[0001] This invention belongs to the field of seismic exploration data processing technology, specifically relating to a pre-stack time migration method and system for undulating surfaces. Background Technology

[0002] Pre-stack time migration is a crucial process in seismic exploration data processing. The results provide vital imaging data for subsequent seismic data interpretation and form the basis for depth migration. Due to its low requirement for velocity accuracy and high computational efficiency, pre-stack time migration has become a widely used imaging method in seismic data processing. Initially, pre-stack time migration was based on horizontal surface migration. Data acquired in complex surface areas required static correction to bring the complex surface data to a fixed horizontal plane before pre-stack time migration could be performed. However, as oil and gas exploration has expanded into areas with complex surfaces and structures, horizontal surface pre-stack migration has become insufficient for processing seismic data in complex areas with significant surface undulations. Therefore, a pre-stack time migration method for undulating surfaces was proposed to address the needs of processing complex surfaces.

[0003] Conventional pre-stack time migration methods for undulating surfaces work as follows: First, a relatively gentle undulating surface (i.e., an undulating reference surface) is generated based on complex surface smoothing. Then, data from gathers sharing a common midpoint are corrected to the corresponding undulating reference surface. This means that the shot and receiver points of each trace within the same gather are corrected to the undulating reference surface at the location of the trace's midpoint. Since the midpoints of all traces within a common midpoint gather are at the same location, traces within the same gather are corrected to the same reference surface, and data from different gathers reside on the undulating reference surface. The common reference surface for a common midpoint gather is the reference elevation of a point on the undulating reference surface, i.e., the reference elevation at the location of the gather's common midpoint. Second, velocity analysis is performed on the undulating surface gathers to obtain velocity model data for the undulating reference surface. During the travel time calculation for pre-stack time migration on undulating surfaces, since the shot and receiver points of the same trace reside on the same reference surface, travel time calculation methods and the undulating surface velocity model are directly used for travel time calculation and migration processing.

[0004] However, conventional pre-stack time migration methods for undulating terrain require calibrating traces within gathers sharing the same common center point to the same reference plane, i.e., the reference plane where the center point is located. When the shot point and receiver point are far apart and have a large elevation difference, the calibration process can introduce significant errors, thereby reducing the accuracy of travel time calculations. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and provide a method and system for pre-stack time migration of undulating surfaces, improve the accuracy of pre-stack time migration travel time calculation, and realize efficient and accurate pre-stack time migration processing in complex surface exploration areas.

[0006] This invention is achieved through the following technical solution:

[0007] A pre-stack time migration method for undulating terrain is provided. The method first corrects the gather data of undulating terrain by correcting the shot point and receiver point of each data to the floating reference plane at the corresponding position. Then, the travel time from the shot point to the imaging point and the travel time from the receiver point to the imaging point are calculated from the floating reference plane of the shot point and the receiver point, respectively. Finally, the total travel time of the shot and receiver points is obtained, and the migration imaging result is calculated.

[0008] A further improvement of the present invention is that the method includes:

[0009] (1) Correction of offset floating reference plane;

[0010] (2) Calculation of the travel time of the firing point;

[0011] (3) Calculation of travel time at the receiver point;

[0012] (4) Calculation of offset imaging results.

[0013] A further improvement of the present invention is that the operation of step (1) includes:

[0014] The elevations of the shot point and the receiver point were respectively corrected to the floating reference planes at their corresponding locations:

[0015] First, based on the shot point coordinates, obtain the floating surface elevation of the shot point location. Then, based on the difference between the floating surface elevation of the shot point location and the original elevation of the shot point location, correct the seismic data to the floating surface elevation corresponding to the shot point.

[0016] Then, based on the coordinates of the receiver point, the elevation of the floating surface at the receiver point location is obtained. The seismic data is then corrected to the floating surface elevation corresponding to the receiver point based on the difference between the floating surface elevation at the receiver point location and the original elevation at the receiver point location.

[0017] A further improvement of the present invention is that the operation of step (2) includes:

[0018] The travel time from the shot point to the imaging point, i.e., the shot point travel time TS, can be calculated using the following travel time calculation formula:

[0019]

[0020] Wherein, TO-SE is the vertical travel time between the imaging point and the shot point, TO is the vertical time from the center point reference plane to the imaging point, SE is the vertical time difference from the shot point to the center point reference plane, and TSH is the horizontal distance conversion time from the shot point to the center point.

[0021] A further improvement of the present invention is that the operation of step (3) includes:

[0022] The travel time from the receiver point to the imaging point, i.e., the receiver point travel time (TR), is calculated using the following travel time formula:

[0023]

[0024] Wherein, TO+RE is the vertical travel time between the imaging point and the detector point, TO is the vertical time from the center point reference plane to the imaging point, RE is the vertical time difference from the detector point to the center point reference plane, and TRH is the horizontal distance conversion time from the detector point to the center point.

[0025] A further improvement of the present invention is that the operation of step (4) includes:

[0026] The total travel time T can be obtained using the following formula: T = TS + TR

[0027] Based on the total travel time, extract the amplitude value at the corresponding time of the input channel and perform offset calculation to obtain the offset result;

[0028] The offset results for each input data channel are calculated sequentially, and then the offset results of all channels are superimposed to obtain the final offset imaging result.

[0029] A second aspect of the present invention provides a pre-stack time migration system for undulating surfaces, the system comprising:

[0030] Offset floating reference plane correction unit, used to correct the elevation of the shot point and the elevation of the receiver point to the floating reference plane at the corresponding positions respectively;

[0031] The shot point travel time calculation unit is connected to the offset floating reference surface correction unit and is used to calculate the shot point travel time.

[0032] The geophone travel time calculation unit is connected to the offset floating reference surface correction unit and is used to calculate the geophone travel time.

[0033] The migration imaging result calculation unit is connected to the shot point travel time calculation unit and the receiver point travel time calculation unit, respectively, and is used to obtain the final migration imaging result based on the shot point travel time and the receiver point travel time.

[0034] A further improvement of the present invention is that the offset floating reference plane correction unit performs the following operations:

[0035] Obtain the coordinates of the shot points and calculate the floating reference surface elevation at the corresponding locations based on the coordinates; simultaneously, obtain the floating reference surface elevation corresponding to the center point of this trace; calculate the difference between the two elevations, calculate the correction time based on the elevation difference, correct the seismic data according to the correction time, and complete the correction process from the shot points to the floating reference surface; at the same time, record the floating surface elevation at the corresponding locations of the shot points in the trace head.

[0036] Obtain the coordinates of the receiver point and calculate the floating reference surface elevation at the corresponding location based on the coordinates; simultaneously obtain the floating reference surface elevation corresponding to the center point of this trace; calculate the difference between the two elevations, calculate the correction time based on the elevation difference, correct the seismic data according to the correction time, complete the correction process from the receiver point to the floating reference surface, and record the floating surface elevation at the corresponding location of the receiver point in the trace head.

[0037] A further improvement of the present invention is that the shot point travel time calculation unit performs the following operations:

[0038] Read the elevation of the floating surface of the shot point in the track head. Calculate the vertical time difference (SE) between the shot point and the center point using the difference between their floating elevations. Calculate the vertical travel time (TO) from the shot point to the imaging point using the vertical time difference (SE) and the vertical travel time (TO) from the center point to the imaging point. Calculate the horizontal distance from the shot point to the center point based on the coordinates of the shot point and the center point. Calculate the horizontal distance time (TSH) using the replacement velocity. After obtaining the vertical and horizontal travel times, calculate the travel time (TS) of the shot point using the travel time calculation formula.

[0039] A further improvement of the present invention is that the detector travel time calculation unit performs the following operations:

[0040] Read the elevation of the floating surface of the geophone at the head of the track. Calculate the vertical time difference (RE) between the geophone and the center point using the difference between the geophone's floating surface elevation and the center point's floating surface elevation. Calculate the vertical travel time (TO) from the geophone to the imaging point using the vertical time difference (RE) and the vertical travel time (TO) from the center point to the imaging point. Calculate the horizontal distance from the geophone to the center point based on the coordinates of the geophone and the center point, and calculate the horizontal distance time (TRH) using the replacement velocity. After obtaining the vertical and horizontal travel times, calculate the travel time (TR) of the geophone according to the travel time calculation formula.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] This invention is based on the pre-stack time migration technique using the Koschhof integral method. It modifies the travel time calculation process to realize a pre-stack time migration processing method for calculating travel time from undulating terrain. This avoids the influence of complex surface static correction processing, improves computational efficiency and imaging effect, and provides an efficient imaging method for pre-stack time migration processing in complex areas.

[0043] This invention eliminates the need to calibrate shot points and receiver points to the same reference plane, reducing the amount of calibration (the calibration process causes errors, and the smaller the calibration amount, the smaller the error), further improving the accuracy of pre-stack time migration travel time calculation, realizing efficient and accurate pre-stack time migration processing in complex surface exploration areas, reducing seismic data processing costs, and improving economic benefits. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the correction for offset floating reference plane;

[0045] Figure 2 A schematic diagram for calculating the travel time of the gun receiver;

[0046] Figure 3 The flowchart of the pre-stack time migration processing for undulating terrain in this invention. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings:

[0048] To address the unsatisfactory static correction and pre-stack time migration effects in seismic processing of complex surface exploration areas, this invention proposes a pre-stack time migration processing method for undulating surfaces, which improves imaging results and provides an efficient imaging method for pre-stack time migration processing in complex areas.

[0049] This invention is based on pre-stack time migration using the Koschhoff integral method. First, it corrects conventional undulating surface gather data, aligning the shot and receiver points of each data point to their corresponding floating reference planes. Second, it modifies the travel time calculation process, calculating the travel time from the shot point to the imaging point (reflection point) and from the receiver to the imaging point, respectively, starting from the floating reference planes of the shot and receiver points. The method mainly includes: floating reference plane correction, shot point travel time calculation, receiver travel time calculation, and finally, obtaining the total shot-receiver travel time and completing the migration imaging result calculation.

[0050] The "floating surface / floating reference surface" mentioned in this invention refers to... Figure 1 The "undulating surface" in the text refers to a relatively gentle undulating surface obtained by smoothing the surface of the actual exploration area.

[0051] The embodiments of the method of the present invention are as follows:

[0052] Example 1

[0053] The method of the present invention includes:

[0054] (1) Correction of offset floating reference plane

[0055] In a conventional floating surface geometries, the shot point and receiver point of each geometries lie on the same reference plane (which can be understood as...). Figure 1The plane containing the red dashed line is the reference plane, and its elevation is consistent with the floating reference plane at the center of the shot-receiver point. Based on this, the present invention corrects the elevations of the shot point and the receiver point to the corresponding floating reference planes. First, based on the shot point coordinates, the floating surface elevation at the shot point location is obtained. Then, based on the difference between the floating surface elevation at the shot point location and the original elevation at the shot point location (i.e., the floating surface elevation at the center of the shot-receiver point), the seismic data is corrected to the floating surface elevation corresponding to the shot point. Then, following the same method, based on the receiver point coordinates, the floating surface elevation at the receiver point location is obtained. Then, based on the difference between the floating surface elevation at the receiver point location and the original elevation at the receiver point location, the seismic data is corrected to the floating surface elevation corresponding to the receiver point. After the shot point and receiver point corrections, the seismic data is generated from the floating surface elevation at the shot point and received at the floating surface elevation at the receiver point, providing seismic data representing an undulating surface for the shot-receiver point travel time calculation.

[0056] (2) Calculation of the travel time of the firing point

[0057] The shot point travel time is calculated based on the travel time from the corrected shot point floating surface position to the imaging point. For example... Figure 2 As shown, the horizontal distance conversion time from the shot point to the center point is TSH, the vertical time from the center point reference plane to the imaging point is TO, and the vertical time difference from the shot point to the center point reference plane is SE. Then, the vertical time from the corresponding elevation of the shot point to the imaging point is TO-SE (in practical applications, the values ​​of TO and SE can be obtained by calculation using known quantities). Based on the vertical travel time between the imaging point and the shot point (i.e., TO-SE) and the velocity of the imaging point position (known quantity, the value of TSH is obtained by calculation using velocity data), the travel time from the shot point to the imaging point is calculated using the travel time calculation formula, such as formula (1).

[0058]

[0059] (3) Calculation of travel time at the receiver point

[0060] The calculation process for the travel time from the receiver point to the imaging point is the same as that for the shot point. First, the vertical travel time of the imaging point is calculated. The vertical elevation difference is calculated based on the surface elevation of the imaging point and the receiver point. The vertical time difference from the surface elevation of the imaging location to the surface elevation of the receiver point is calculated using the velocity model and the vertical elevation difference. Finally, the vertical travel time between the imaging point and the receiver point (i.e., TO+RE) is obtained. According to the travel time calculation formula, such as formula (2), TO is the vertical time from the center point reference plane to the imaging point, and RE is the vertical time difference from the receiver point to the center point reference plane. TRH is the converted time of the horizontal distance from the receiver point to the center point. The travel time from the receiver point to the imaging point is calculated using the vertical travel time and the horizontal distance from the receiver point to the center point (the value of TRH can be obtained by calculating the horizontal distance).

[0061]

[0062] (4) Calculation of migration imaging results

[0063] After the shot point travel time (TS) and receiver point travel time (TR) are calculated, the two travel times are added together to obtain the total travel time (T), as shown in formula (3). Based on the total travel time, the amplitude value at the corresponding time (total travel time) of the input channel is extracted for offset calculation to obtain the offset result. The offset result of each input data is calculated in sequence, and then the offset results of each channel are superimposed to obtain the final offset imaging result.

[0064] T = TS + TR (3)

[0065] The present invention also provides a pre-stack time migration system for undulating surfaces, an embodiment of which is as follows:

[0066]

Example 2

[0067] The system of the present invention includes:

[0068] Offset floating reference plane correction unit, used to correct the elevation of the shot point and the elevation of the receiver point to the floating reference plane at the corresponding positions respectively;

[0069] The shot point travel time calculation unit is connected to the offset floating reference surface correction unit and is used to calculate the shot point travel time.

[0070] The geophone travel time calculation unit is connected to the offset floating reference surface correction unit and is used to calculate the geophone travel time.

[0071] The migration imaging result calculation unit is connected to the shot point travel time calculation unit and the receiver point travel time calculation unit, respectively, and is used to obtain the final migration imaging result based on the shot point travel time and the receiver point travel time.

[0072] The process of using the system for pre-stack time migration processing is as follows: Figure 3 As shown:

[0073] The first step is to correct the floating datum elevation of the shot points. Read one seismic data track, obtain the coordinates of the shot points, and calculate the corresponding floating datum elevation. Simultaneously, obtain the floating datum elevation corresponding to the center point of this track. Calculate the difference between the two elevations, and calculate the correction time based on the elevation difference. Correct the seismic data according to the correction time, completing the correction process from the shot points to the floating datum. At the same time, record the floating datum elevation at the corresponding shot point location in the track header.

[0074] The second step is the elevation correction of the floating reference surface at the receiver point. One seismic data track (the same track as the one read in the first step) is read to obtain the coordinates of the receiver points. The elevation of the floating reference surface at the corresponding location is calculated based on the coordinates. Simultaneously, the elevation of the floating reference surface corresponding to the center point of this track is also obtained. The difference between the two elevations is calculated, and the correction time is calculated based on the elevation difference. The seismic data is then corrected according to the correction time, completing the correction process from the receiver point to the floating reference surface. At the same time, the floating reference surface elevation at the corresponding location of the receiver point is recorded in the track header.

[0075] The third step is to calculate the shot point travel time. Read the elevation of the floating surface of the shot point in the track head. Calculate the vertical time difference (SE) between the shot point and the center point using the difference between their floating surface elevations. Calculate the vertical travel time (TO) from the shot point to the imaging point using the vertical time difference (SE) and the vertical travel time (TO) from the center point to the imaging point. Calculate the horizontal distance from the shot point to the center point based on the shot point coordinates and the center point coordinates. Calculate the horizontal distance time (TSH) using the replacement velocity. After obtaining the vertical and horizontal travel times, calculate the shot point travel time (TS) using the travel time calculation formula.

[0076] Step 4: Calculate the travel time of the receiver point. Read the elevation of the floating surface of the receiver point in the track head. Calculate the vertical time difference (RE) between the receiver point and the center point using the difference between their floating surface elevations. Calculate the vertical travel time (TO) from the receiver point to the imaging point using the vertical time difference (RE) and the vertical travel time (TO) from the center point to the imaging point. Calculate the horizontal distance (TRH) from the receiver point to the center point based on the receiver point coordinates and the center point coordinates. Calculate the horizontal distance time (TRH) using the replacement velocity. After obtaining the vertical and horizontal travel times, calculate the travel time (TR) of the receiver point using the travel time calculation formula.

[0077] Step 5: Total travel time calculation and offset. The shot point travel time TS obtained in step 3 is added to the receiver point travel time TR obtained in step 4 to obtain the total travel time T. Using the total travel time, the amplitude values ​​at the corresponding time points of the input channel are extracted for offset calculation, and the offset result is obtained.

[0078] Step 6: Image result output. Following the above five steps, the offset result of each input data is calculated sequentially. Then, the offset results of all channels are superimposed to obtain the final offset imaging result, which is then output. The pre-stack time migration processing is complete.

[0079] This invention, based on conventional undulating surface migration methods, designs a pre-stack time migration processing method and system for undulating surfaces. It mainly calculates migration imaging results by correcting the elevation of shot and receiver points, calculating vertical travel time, shot point travel time, receiver travel time, and obtaining the total travel time of the shot and receiver points. This invention corrects shot and receiver points in the same trace to the corresponding undulating reference surface, calculates travel time starting from the floating reference surface of the shot and receiver points, and completes pre-stack time migration processing. This further improves the accuracy of pre-stack time migration travel time calculation, achieving efficient and accurate pre-stack time migration processing in complex surface exploration areas, reducing seismic data processing costs, and improving economic efficiency.

[0080] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0081] In the description of this invention, unless otherwise stated, the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0082] The above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the technical solutions described in the specific embodiments of the present invention. Therefore, the foregoing description is only a preferred option and is not restrictive.

Claims

1. A pre-stack time migration method for undulating surfaces, characterized in that: The method first corrects the undulating surface gather data by aligning the shot point and receiver point of each data point to the corresponding floating reference plane. Then, it calculates the travel time from the shot point to the imaging point and the travel time from the receiver point to the imaging point, respectively, starting from the floating reference planes of the shot point and receiver point. Finally, it obtains the total travel time of the shot and receiver points and completes the calculation of the migration imaging results.

2. The pre-stack time migration method for undulating terrain according to claim 1, characterized in that: The method includes: (1) Correction of offset floating reference plane; (2) Calculation of the travel time of the firing point; (3) Calculation of travel time at the receiver point; (4) Calculation of offset imaging results.

3. The pre-stack time migration method for undulating surfaces according to claim 2, characterized in that: The operation of step (1) includes: The elevations of the shot point and the receiver point were respectively corrected to the floating reference planes at their corresponding locations: First, based on the shot point coordinates, obtain the floating surface elevation of the shot point location. Then, based on the difference between the floating surface elevation of the shot point location and the original elevation of the shot point location, correct the seismic data to the floating surface elevation corresponding to the shot point. Then, based on the coordinates of the receiver point, the elevation of the floating surface at the receiver point location is obtained. The seismic data is then corrected to the floating surface elevation corresponding to the receiver point based on the difference between the floating surface elevation at the receiver point location and the original elevation at the receiver point location.

4. The pre-stack time migration method for undulating surfaces according to claim 2, characterized in that: The operation of step (2) includes: The travel time from the shot point to the imaging point, i.e., the shot point travel time TS, can be calculated using the following travel time calculation formula: Wherein, TO-SE is the vertical travel time between the imaging point and the shot point, TO is the vertical time from the center point reference plane to the imaging point, SE is the vertical time difference from the shot point to the center point reference plane, and TSH is the horizontal distance conversion time from the shot point to the center point.

5. The pre-stack time migration method for undulating surfaces according to claim 2, characterized in that: The operation of step (3) includes: The travel time from the receiver point to the imaging point, i.e., the receiver point travel time (TR), is calculated using the following travel time formula: Wherein, TO+RE is the vertical travel time between the imaging point and the detector point, TO is the vertical time from the center point reference plane to the imaging point, RE is the vertical time difference from the detector point to the center point reference plane, and TRH is the horizontal distance conversion time from the detector point to the center point.

6. The pre-stack time migration method for undulating surfaces according to claim 2, characterized in that: The operation of step (4) includes: The total travel time T can be obtained using the following formula: T = TS + TR Based on the total travel time, extract the amplitude value at the corresponding time of the input channel and perform offset calculation to obtain the offset result; The offset results for each input data channel are calculated sequentially, and then the offset results of all channels are superimposed to obtain the final offset imaging result.

7. A pre-stack time migration system for undulating surfaces, characterized in that: The system includes: Offset floating reference plane correction unit, used to correct the elevation of the shot point and the elevation of the receiver point to the floating reference plane at the corresponding positions respectively; The shot point travel time calculation unit is connected to the offset floating reference surface correction unit and is used to calculate the shot point travel time. The geophone travel time calculation unit is connected to the offset floating reference surface correction unit and is used to calculate the geophone travel time. The migration imaging result calculation unit is connected to the shot point travel time calculation unit and the receiver point travel time calculation unit, respectively, and is used to obtain the final migration imaging result based on the shot point travel time and the receiver point travel time.

8. The pre-stack time migration system for undulating surfaces according to claim 7, characterized in that: The offset floating reference plane correction unit performs the following operations: Obtain the coordinates of the shot points and calculate the floating reference surface elevation at the corresponding locations based on the coordinates; simultaneously, obtain the floating reference surface elevation corresponding to the center point of this trace; calculate the difference between the two elevations, calculate the correction time based on the elevation difference, correct the seismic data according to the correction time, and complete the correction process from the shot points to the floating reference surface; at the same time, record the floating surface elevation at the corresponding locations of the shot points in the trace head. Obtain the coordinates of the receiver point and calculate the floating reference surface elevation at the corresponding location based on the coordinates; simultaneously obtain the floating reference surface elevation corresponding to the center point of this trace; calculate the difference between the two elevations, calculate the correction time based on the elevation difference, correct the seismic data according to the correction time, complete the correction process from the receiver point to the floating reference surface, and record the floating surface elevation at the corresponding location of the receiver point in the trace head.

9. The pre-stack time migration system for undulating surfaces according to claim 7, characterized in that: The gun point travel time calculation unit performs the following operations: Read the elevation of the floating surface of the shot point in the track head. Calculate the vertical time difference (SE) between the shot point and the center point using the difference between their floating elevations. Calculate the vertical travel time (TO) from the shot point to the imaging point using the vertical time difference (SE) and the vertical travel time (TO) from the center point to the imaging point. Calculate the horizontal distance from the shot point to the center point based on the coordinates of the shot point and the center point. Calculate the horizontal distance time (TSH) using the replacement velocity. After obtaining the vertical and horizontal travel times, calculate the travel time (TS) of the shot point using the travel time calculation formula.

10. The pre-stack time migration system for undulating surfaces according to claim 7, characterized in that: The detector travel time calculation unit performs the following operations: Read the elevation of the floating surface of the geophone at the head of the track. Calculate the vertical time difference (RE) between the geophone and the center point using the difference between the geophone's floating surface elevation and the center point's floating surface elevation. Calculate the vertical travel time (TO) from the geophone to the imaging point using the vertical time difference (RE) and the vertical travel time (TO) from the center point to the imaging point. Calculate the horizontal distance from the geophone to the center point based on the coordinates of the geophone and the center point, and calculate the horizontal distance time (TRH) using the replacement velocity. After obtaining the vertical and horizontal travel times, calculate the travel time (TR) of the geophone according to the travel time calculation formula.

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