Method for drawing thickness points of 1% sediment of seabed

Abstract

The invention provides a method for drawing thickness points of 1% sediment of a seabed. The method belongs to the technical field of marine surveying and mapping, submarine topography and landform mapping and submarine science. The method comprises the following steps: interpreting and exporting horizon data of a seabed and a basement surface through Geoframe software; cleaning and sorting the horizon data to obtain horizon data of a single measuring line; performing layer data cutting, interpolation complementing, subtraction and time-depth conversion to calculate the thickness of the sediment in the depth domain; calculating 1% sediment thickness points on each measuring line; and drawing the seabed surface, the substrate surface, the sediment thickness, the FOS point coordinates and the 1% sediment thickness point into a profile map, and drawing a plane distribution map of the 1% sediment thickness point by using QGIS software. According to the method, through interpretation of the long cable seismic section, the accuracy of calculation of the 1% sediment thickness point is guaranteed to the maximum extent by utilizing the high-precision time-depth conversion relation, and the requirement for calculation of the 1% sediment thickness in the 761th item of the ocean method convention of the United National is met.

Description

Technical Field

[0001] The present disclosure relates to the fields of ocean surveying and mapping, seabed topography and landform mapping, and seabed science and technology, and in particular to a method for mapping points with a 1% sediment thickness on the seabed. Background Art

[0003] According to relevant regulations, the continental shelf of a coastal state includes all natural extensions of its land territory beyond its territorial waters, and extends to the seabed and subsoil of the submarine area at the outer edge of the continental margin: if the distance from the territorial sea baseline to the outer edge of the continental margin is less than 200 nautical miles, it is extended to 200 nautical miles; if it exceeds 200 nautical miles, the continental shelf beyond 200 nautical miles can be claimed. Figure 8 When claiming a continental shelf beyond 200 nautical miles, coastal states can use two methods to define the outer limit of their continental shelf: the sediment thickness formula method, which requires that the sediment thickness at each point constituting the outer limit be at least 1% of the shortest distance from that point to the foot of the continental slope; and the distance formula method, which requires that the distance between each point constituting the outer limit and the foot of the continental slope does not exceed 60 nautical miles. Clearly, the calculation and determination of the 1% sediment thickness point plays a key role in coastal states' efforts to extend their continental shelf beyond 200 nautical miles.

[0004] Sediment thickness can be determined using both direct sampling and indirect methods. Direct sampling involves drilling. Drilling, particularly deepwater drilling, is expensive and only yields point-by-point values. Indirect methods, such as multi-beam seismic surveys and gravity inversion, are less expensive, can be performed more quickly, and can provide information on sediment distribution along survey lines or interfaces. The Commission on the Limits of the Continental Shelf considers multi-channel seismic reflection data the most robust source of evidence for determining sediment thickness due to the high overall quality and penetration of multi-channel data, as well as its inherent velocity information, which facilitates the delineation of the outer edges of the continental margin.

[0005] At present, the calculation method for 1% sediment thickness point comes from Geocap software developed by Geodata, Norway, or CARISLOTS software developed by Teledyne CARIS, Canada, but the algorithms of these two software are not disclosed. In addition, when it comes to a large number of calculations of multiple seismic lines, using Geocap software to carry out time-depth conversion and calculate 1% sediment thickness point one by one will bring a huge workload. In addition, Geocap software can only provide the plane coordinates of 1% sediment thickness point and cannot map important information such as seabed surface, basement surface, sediment thickness, sediment thickness point, 1% thickness line onto a profile diagram for easy analysis and comparison. Therefore, in view of the problems and technical requirements of the prior art, the purpose of the present invention is to provide an accurate, fast and convenient determination of 1% sediment thickness point and a mapping method. Summary of the Invention

[0006] One technical problem to be solved by the present disclosure is that existing calculation methods require a large amount of manpower and material resources, and at the same time, it is impossible to form cross-sectional views that can display the seabed surface, basement surface, sediment thickness, 1% sediment thickness points, and 1% thickness lines, etc.

[0007] To solve the above technical problem, an embodiment of the present disclosure provides a method for drawing 1% sediment thickness points on the seabed, which includes: S1. Collect sgy seismic data and import the sgy seismic data into the Geoframe seismic interpretation software for interpretation to obtain the time-depth data of the seabed surface and basement surface of all seismic lines; S2. Use the multi-line horizon data cleaning subsystem to clean the time-depth data of the seabed surface and basement surface of all seismic lines in S1, remove the error data rows generated during the export of Geoframe, and obtain the correct horizon data; S3. Use the line sorting subsystem to split the correct horizon data in S2 one by one according to the line name and store it in a folder named separately by the line name; S4. Use the formation sediment thickness calculation subsystem to calculate the depth-domain sediment thickness of each line sorted out in S3; S5. Use the Geocap software and high-precision measured terrain data to determine the longitude and latitude coordinates of the FOS points corresponding to each line; S6. Use the 1% sediment thickness point calculation subsystem. According to the depth-domain sediment thickness of each line obtained in S4 and the longitude and latitude coordinates of the corresponding FOS points obtained in S5, collect the points where the sediment thickness at each point on the line is greater than 1% of the distance from the point to the FOS point. This point is the 1% sediment thickness point; S7. Based on the data in S6, draw the seabed surface - basement surface depth map, sediment thickness map, and the position map of 1% sediment thickness points to display the specific positions of the FOS points and 1% sediment thickness points.

[0008] In some embodiments, for the aforementioned method for drawing 1% sediment thickness points on the seabed, the single-line folder in S3 includes the seabed surface line and basement surface line data.

[0009] In some embodiments, for the aforementioned method for drawing 1% sediment thickness points on the seabed, the calculation method in S4 includes: S41. Read the horizon data of the seabed surface and basement surface data, select the horizon data with continuous CDP, or select the discontinuous horizon data with an interruption less than 100m and use the piecewise Hermite interpolation polynomial to fill it up to ensure the continuity and accuracy of the data; S42. Trim the seafloor surface and the base surface in S41 so that the seafloor surface and the base surface completely coincide and are aligned to obtain a continuous seafloor surface and base surface with the same length. S43. Subtract the seafloor surface from the base surface to obtain the sediment thickness in the time domain. S44. Use the time-depth conversion formula constrained by ocean drilling to convert the sediment thickness in the time domain into the sediment thickness in the depth domain.

[0010] In some embodiments, for the aforementioned method of plotting the 1% sediment thickness points on the seafloor, when the layer data with an interruption greater than 100 m appears in S41, it indicates an error in the layer data, and it is necessary to return to S1 to check the original seismic data in Geoframe.

[0011] In some embodiments, for the aforementioned method of plotting the 1% sediment thickness points on the seafloor, where The seafloor surface and the base surface obtained in S42 can be compared with the overlapping parts of the seafloor surface and the base surface in the Geoframe seismic interpretation software to determine the accuracy of the results in S42.

[0012] In some embodiments, for the aforementioned method of plotting the 1% sediment thickness points on the seafloor, the determination method of the 1% sediment thickness points in S6 includes: S61. Read the longitude and latitude coordinates of all FOS points and the corresponding survey line names, and match the FOS point coordinates with the survey line according to the survey line name. S62. Calculate the straight-line distance from each point corresponding to the CDP on the survey line to the FOS point to obtain the first distance. S63. Calculate the ratio of the sediment thickness in the depth domain of each point corresponding to the CDP to the first distance to obtain a number of first ratios. All points with the first ratio greater than 0.01 are 1% sediment thickness points. S64. Export the xy coordinates, time-domain thickness, depth-domain thickness, CDP number, first distance, first ratio, and the index number in the original coordinate column of all 1% sediment thickness points that meet the conditions, and export the 1% sediment thickness point farthest from the FOS point.

[0013] In some embodiments, for the aforementioned method of plotting the 1% sediment thickness points on the seafloor, the plotting method in S7 includes: S71. Automatically read the sediment thickness data, seafloor surface and base surface depth data, FOS point coordinates, and 1% sediment thickness points that meet the conditions of all survey lines. S72. Calculate the azimuth of the survey line in the direction of increasing CDP. Among them, when the azimuth is between 67.5° and -112.5°, it is a reverse hand section, and the drawing is made in the decreasing CDP manner to ensure that the final view is in the forward hand section direction. S73. Draw the upper sub - figure, including four pieces of information: FOS points, 1% sediment thickness points, sediment thickness, and 1% thickness line; S74. Draw the lower sub - figure, including the seabed depth and basement depth information; S75. Draw the planar distribution map of 1% sediment thickness points, including the planar distribution information of 1% sediment thickness points.

[0014] Through the above - mentioned technical solution, a method for drawing 1% sediment thickness points on the seabed provided by the present disclosure, based on the sea - floor horizon and basement horizon data interpreted by Geoframe seismic interpretation software, first cleans and sorts the exported data to obtain the seismic data after cleaning for a single survey line; then truncates both ends of the seabed surface and basement surface of this survey line, and interpolates and fills the data missing due to data cleaning, that is, obtains the seabed surface and basement surface with completely continuous CDP. After that, subtract the time - domain depth value of the seabed surface from the time - domain depth value of the basement surface to obtain the sediment thickness in the time domain; then convert the sediment thickness in the time domain into the sediment thickness in the depth domain according to the time - depth conversion formula; combine the longitude and latitude coordinates of the FOS points to calculate all the points on the seismic survey line that meet the 1% sediment thickness points; finally, draw the seabed surface and basement surface in the depth domain, as well as the sediment thickness, FOS point coordinates, 1% sediment thickness points, and 1% thickness line into a cross - section diagram, and can draw the distribution range of 1% sediment thickness points on the plane through QGIS software. Through the interpretation of long - cable seismic profiles, the present invention uses a high - precision time - depth conversion relationship to maximize the accuracy of calculating 1% sediment thickness points. At the same time, according to the selection, multiple seismic data can be processed at one time, greatly saving labor costs under a large amount of data, and meeting the requirements for calculating 1% sediment thickness in Article 76 of the United Nations Convention on the Law of the Sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present disclosure. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0016] Figure 1 is a flowchart of a method for drawing 1% sediment thickness points on the seabed disclosed in Embodiment 1 of the present disclosure; Figure 2 is a partial position diagram of a long - cable multi - channel seismic survey line in a method for drawing 1% sediment thickness points on the seabed disclosed in Embodiment 1 of the present disclosure; Figure 3It is a cross-sectional view of the NH2 multi-channel seismic line in a method for plotting the 1% sediment thickness points on the seabed disclosed in an embodiment of the present disclosure; Figure 4 It is a cross-sectional view of the NH3 multi-channel seismic line in a method for plotting the 1% sediment thickness points on the seabed disclosed in an embodiment of the present disclosure; Figure 5 It is a calculation result diagram of relevant elements for continental shelf delimitation of the NH2 line in a method for plotting the 1% sediment thickness points on the seabed disclosed in an embodiment of the present disclosure; Figure 6 It is a calculation result diagram of relevant elements for continental shelf delimitation of the NH3 line in a method for plotting the 1% sediment thickness points on the seabed disclosed in an embodiment of the present disclosure; Figure 7 It is a partial plan position diagram of the 1% sediment thickness points meeting the conditions in the multi-channel seismic line in a method for plotting the 1% sediment thickness points on the seabed disclosed in Embodiment 1 of the present disclosure; Figure 8 It is a schematic diagram of the rules for continental shelf delimitation in a method for plotting the 1% sediment thickness points on the seabed of the present disclosure. Detailed implementation manners

[0017] The following further describes the implementation manners of the present disclosure in detail with reference to the drawings and embodiments. The detailed description and drawings of the following embodiments are used to exemplarily illustrate the principle of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms, not limited to the specific embodiments disclosed herein, but including all technical solutions falling within the scope of the claims.

[0018] These embodiments are provided by the present disclosure to make the present disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions and values described in these embodiments should be interpreted as merely exemplary, rather than as limitations.

[0019] All terms used in the present disclosure have the same meaning as understood by those of ordinary skill in the art to which the present disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, such as those, should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0020] For technologies, methods, and devices known to those of ordinary skill in the relevant field, detailed discussions may not be made, but where appropriate, the technologies, methods, and devices should be regarded as part of the specification.

[0021] Embodiment 1 Refer to the attachedFigure 1 , 2 , 3, and 4, this embodiment discloses a method for plotting the 1% sediment thickness points on the seabed, which includes: S1. Collect sgy seismic data, import the sgy seismic data into the Geoframe seismic interpretation software for interpretation to obtain the time-depth data of the seabed surface and the basement surface, and export the seabed surface and basement surface data of all seismic lines. In this embodiment, 2 lines are set, namely NH2 and NH3, S2. Use the multi-line horizon data cleaning subsystem to export the interpreted horizons in a specific format program, check all the interpreted horizon data, that is, the time-depth data of the seabed surface and the basement surface, output the correct lines from all the data and record the number of correct lines at the same time, and delete the wrong lines and count the number of wrong lines, and the final result can be counted to ensure that the subsequent sorting is all correct data.

[0022] S3. Use the line sorting subsystem to split each of the cleaned correct seismic lines one by one, name them separately, and put the time-depth data of the seabed surface and the basement surface corresponding to the lines into the corresponding line folders, that is, the NH2 and NH3 folders, and check whether each separate folder contains the seabed surface and basement surface two horizon files. If any one of the horizon files is not displayed, the program will prompt that the original file needs to be rechecked to ensure that there are no errors. It can be understood that the seabed surface and the basement surface are the key factors for determining the final sediment thickness. The farthest 1% sediment thickness point needs to be determined by the relative positions of the seabed surface and the basement surface, and an accurate cross-section needs to be drawn. Therefore, it is necessary to ensure that each line folder contains the seabed surface and basement surface two horizon files; S4. Use the formation sediment thickness calculation subsystem. It is necessary to select the horizon data with continuous CDP in the seabed surface and the basement surface, and at the same time crop the data to align the positions of the seabed surface and the basement surface of the same CDP. Then, when drawing a picture with this data, the picture is continuous and uninterrupted. When calculating the sediment thickness, subtract the seabed surface from the basement surface to obtain the sediment thickness in the time domain, as Figure 3 and Figure 4 shown, and then through the time-depth conversion formula (1) obtained from the South China Sea Ocean Drilling Well U1433, the sediment thickness in the depth domain is obtained, z = 0.000188295t 2 + 0.695896t (1) where z is the sediment thickness in the depth domain and t is the sediment thickness in the time domain, and export the depth domain thickness of each line; S5. Use the Geocap software and the high-precision measured terrain data to determine the longitude and latitude coordinates of the FOS points of each line; S6. Use the 1% sediment thickness point calculation subsystem to calculate all 1% sediment thickness points that meet the conditions. First, read the longitude and latitude coordinates of the FOS points of NH2 and NH3 determined in step S5, and calculate whether the ratio of the sediment thickness at each CDP corresponding point on the survey line to the straight-line distance (i.e., the first distance) from this point to the FOS point is greater than 0.01. If the first ratio is greater than 0.01, then this point is the 1% sediment thickness point. Export the xy coordinates, time-domain thickness, depth-domain thickness, CDP number, first distance, first ratio, and the index number in the original coordinate column of all 1% sediment thickness points that meet the conditions, and export the 1% sediment thickness point farthest from the FOS as the basis for drawing. Here, CDP is the common depth point gather.

[0023] S7. Based on the data in S4, S5, and S6, draw the seabed - basement depth map, sediment thickness map, and 1% sediment thickness point map to show the specific positions of the 1% sediment thickness points. Specifically, refer to Figure 5 , Figure 6 and Figure 7 , calculate the azimuth of the survey line in the direction of increasing CDP. Among them, when the azimuth is between 67.5° and -112.5°, it is a reverse hand profile, and the drawing is done in the decreasing CDP manner so that the final view shows the forward hand profile direction. Specifically, the azimuth of NH2 is -24°, and the azimuth of NH3 is 65°. The azimuth calculation method is as follows: find the spatial coordinates (x1, y1) and (x n , y n ) corresponding to the first CDP and the last CDP of each survey line; calculate the direction vector (x n - x1, y n - y1); calculate the angle between the direction vector and the y-axis, which is the azimuth. From the upper subfigure, the sediment thickness at each CDP on the survey line can be known. The position of the FOS point is at the blue inverted triangle, and the dotted line is the 1% thickness line. Among them, the 1% thickness line starts from the FOS point and extends to both ends of the survey line, and the slope of the spatial distance is 0.01, which can be used as a reference line for whether it meets the 1% sediment thickness point. Specifically, the ratio of the sediment thickness value corresponding to any point on this line to the first distance of this point is equal to 0.01. That is, if the sediment thickness value at a certain CDP is higher than the thickness value on the 1% thickness line at this CPD, then this point meets the condition of the 1% sediment thickness point. Refer to Figure 5 and Figure 6In the upper sub - figure, for the red region on the abscissa, when determining the continental shelf boundary, the point farthest from the FOS point is selected from the red region as the outer limit of the continental shelf. From the lower sub - figure, the seabed depth and the basal surface depth information of NH2 and NH3 can be obtained respectively. The seabed position is the lined region, and the basal surface is the filled region. The sediment thickness is zero at the junction of the basal surface and the seabed. Therefore, through the upper and lower sub - figures, more comprehensive data on various aspects of this survey line can be understood, as well as the integration of the data. Compared with the traditional method of separately displaying individual indicators and requiring manual comparison and calculation, the calculation precision is greatly improved.

[0024] So far, the embodiments of the present disclosure have been described in detail. To avoid obscuring the concept of the present disclosure, some details well - known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed here based on the above description.

[0025] Although some specific embodiments of the present disclosure have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustration only and not for limiting the scope of the present disclosure. Those skilled in the art should understand that the above embodiments can be modified or some technical features can be equivalently replaced without departing from the scope and spirit of the present disclosure. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way.

Claims

1. A method for plotting the 1% sediment thickness points on the seabed, characterized in that, Including: S1. Collect sgy seismic data, import the sgy seismic data into the Geoframe seismic interpretation software for interpretation to obtain the time-depth data of the seafloor surface and the basement surface of all seismic lines; S2. Use the multi-line horizon data cleaning subsystem to clean the time-depth data of the seafloor surface and the basement surface of all seismic lines in S1, remove the error data rows generated during the export from Geoframe, and obtain the correct horizon data; S3. Use the seismic line sorting subsystem to split the correct horizon data in S2 one by one according to the seismic line name and store them in a folder named separately by the seismic line name; S4. Use the formation sediment thickness calculation subsystem to calculate the sediment thickness in the depth domain of each seismic line sorted out in S3; S5. Use the Geocap software and high-precision measured terrain data to determine the longitude and latitude coordinates of the FOS points corresponding to each seismic line; S6. Use the 1% sediment thickness point calculation subsystem. According to the sediment thickness in the depth domain of each seismic line obtained in S4 and the longitude and latitude coordinates of the corresponding FOS points obtained in S5, collect the points where the sediment thickness at each point on the seismic line is greater than 1% of the distance from this point to the FOS point, and this point is the 1% sediment thickness point; S7. Based on the data in S6, draw the seafloor surface - basement surface depth map, sediment thickness map, and 1% sediment thickness point position map to display the specific positions of the FOS points and the 1% sediment thickness points.

2. The mapping method of the 1% sediment thickness point on the seabed according to claim 1, wherein, The single seismic line folder in S3 includes the seafloor surface seismic line and the basement surface seismic line data.

3. A method for drawing the 1% sediment thickness points on the seabed according to claim 1, characterized in that The calculation method in S4 includes: S41. Read the horizon data of the seafloor surface and the basement surface, select the horizon data with continuous CDP, or select the discontinuous horizon data with a break less than 100m and use the piecewise Hermite interpolation polynomial to fill it up to ensure the continuity and accuracy of the data; S42. Trim the seafloor surface and the basement surface in S41 so that the seafloor surface and the basement surface completely coincide and are aligned to obtain a continuous and consistent-length seafloor surface and basement surface; S43. Subtract the seafloor surface from the basement surface to obtain the sediment thickness in the time domain; S44. Use the time-depth conversion formula constrained by ocean drilling to convert the sediment thickness in the time domain into the sediment thickness in the depth domain.

4. A method for drawing the 1% sediment thickness points on the seabed according to claim 3, characterized in that When the discontinuous horizon data in S41 has a break greater than 100m, it is an error in the horizon data, and it is necessary to return to S1 to check the original seismic data in Geoframe.

5. A method for drawing the 1% sediment thickness points on the seabed according to claim 3, characterized in that The obtained seafloor surface and basement surface in S42 can be compared with the overlapping parts of the seafloor surface and the basement surface in the Geoframe seismic interpretation software to determine the accuracy of the results in S42.

6. A method for drawing the 1% sediment thickness points on the seabed according to claim 1, characterized in that The determination method of the 1% sediment thickness points in S6 includes: S61. Read the longitude and latitude coordinates of all FOS points and the corresponding survey line names, and match the FOS point coordinates with the survey lines according to the survey lines. S62. Calculate the straight-line distance from the point corresponding to each CDP on the survey line to the FOS point to obtain the first distance. S63. Calculate the ratio of the sediment thickness in the depth domain of the point corresponding to each CDP to the first distance to obtain a number of first ratios. All points with the first ratio greater than 0.01 are 1% sediment thickness points. S64. Export the xy coordinates, thickness in the time domain, thickness in the depth domain, CDP number, first distance, first ratio, and the index number in the original coordinate column of all 1% sediment thickness points that meet the conditions, and export the 1% sediment thickness point farthest from the FOS point.

7. According to a method for drawing 1% sediment thickness points on the seabed according to claim 1, characterized in that The drawing method in S7 includes: S71. Automatically read the sediment thickness data, seabed surface and basement depth data, FOS point coordinates, and 1% sediment thickness points that meet the conditions of all survey lines. S72. Calculate the azimuth of the survey line in the direction of increasing CDP. Among them, the azimuth between 67.5° and -112.5° is a reverse hand section, and the drawing is made in the decreasing order of CDP to ensure that the final view is in the forward hand section direction. S73. Draw the upper subgraph, including four information: FOS point, 1% sediment thickness point, sediment thickness, and 1% thickness line. S74. Draw the lower subgraph, including the seabed surface depth and basement depth information. S75. Draw the plane distribution map of 1% sediment thickness points, including the plane distribution information of 1% sediment thickness points.

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