A method for plotting 1% sediment thickness points on the sea floor

Abstract

The present disclosure provides a method for drawing a 1% sediment thickness point of the seabed. It belongs to the field of marine surveying and mapping, seabed topography mapping and seabed science and technology, and the method comprises the following steps: interpreting and exporting the horizon data of the seabed and the base surface by Geoframe software; cleaning and sorting the horizon data to obtain the horizon data of a single survey line; cutting, interpolating, subtracting and time-depth conversion of the horizon data to calculate the sediment thickness in the depth domain; calculating the 1% sediment thickness point on each survey line; drawing the seabed surface, the base surface, the sediment thickness, the FOS point coordinates and the 1% sediment thickness point into a profile, and drawing the planar distribution map of the 1% sediment thickness point by QGIS software. The present disclosure guarantees the accuracy of the calculation of the 1% sediment thickness point to the maximum extent by interpreting the long cable seismic profile and using the high-precision time-depth conversion relationship, and meets the requirements of the calculation of the 1% sediment thickness point in the 76th article of the United Nations Convention on the Law of the Sea.

Description

Technical Field

[0001] This disclosure relates to the fields of marine surveying, seabed topography mapping, and seabed science and technology, and in particular to a method for mapping points representing 1% of the seabed sediment thickness. Background Technology

[0002] According to relevant regulations, a coastal state's continental shelf includes the entire natural prolongation of its land territory beyond its territorial sea, extending to the seabed and subsoil of the submarine area reaching the outer edge of the continental margin: if the distance from the baseline of the territorial sea to the outer edge of the continental margin is less than 200 nautical miles, it extends to 200 nautical miles; if it exceeds 200 nautical miles, the continental shelf beyond 200 nautical miles can be claimed. Figure 8 As shown, when coastal states claim a continental shelf beyond 200 nautical miles, they can use two methods to delineate the outer limits of their continental shelf: one is the sedimentary thickness formula method, where the sedimentary thickness at each fixed point constituting the outer limit is at least 1% of the shortest distance from that point to the foot of the continental slope; the other is the distance formula method, where the distance between each fixed point constituting the outer limit and the foot of the continental slope does not exceed 60 nautical miles. Clearly, if a coastal state wants to extend its continental shelf beyond 200 nautical miles, the calculation and determination of the 1% sedimentary thickness point plays a crucial role.

[0003] Sediment thickness can be determined using both direct sampling and indirect methods. Direct sampling is conducted through drilling. Drilling, especially deep-water drilling, is expensive and only yields data for a single point. Indirect methods include multibeam seismometry and gravity inversion, which are less expensive, faster, and can provide information on sediment distribution along survey lines or interfaces. Because multichannel data has high overall quality and penetration, and includes velocity information, it is beneficial for delineating the outer boundaries of continental shelves. The Commission on the Limits of the Continental Shelf considers multichannel seismic reflection data to be the most compelling source of evidence for determining sediment thickness.

[0004] Currently, the methods for calculating 1% sediment thickness points come from Geocap software developed by Geodata in Norway or CARISLOTS software developed by TeledyneCARIS in Canada, but the algorithms for these two software programs are not publicly available. Furthermore, when dealing with numerous calculations involving multiple seismic lines, using Geocap software for individual time-depth conversions and calculations of 1% sediment thickness points would be extremely labor-intensive. In addition, Geocap software can only provide the planar coordinates of the 1% sediment thickness points and cannot plot important information such as the seabed surface, basement surface, sediment thickness, sediment thickness points, and 1% thickness lines onto a single cross-sectional diagram that facilitates analysis and comparison. Therefore, addressing the problems and technical requirements of existing technologies, the purpose of this invention is to provide an accurate, fast, and convenient method for determining and mapping 1% sediment thickness points. Summary of the Invention

[0005] One of the technical problems that this disclosure aims to solve is that existing calculation methods require a lot of human and material resources and cannot generate cross-sectional diagrams that can display the seabed surface, base surface, sediment thickness, 1% sediment thickness points, and 1% thickness lines.

[0006] To address the aforementioned technical problems, this disclosure provides a method for mapping points representing 1% of the seabed sediment thickness, comprising:

[0007] S1. Collect sgy seismic data and import the sgy seismic data into Geoframe seismic interpretation software for interpretation to obtain time-depth data of the seabed and base surface of all seismic survey lines.

[0008] S2. Use the multi-line stratigraphic data cleaning subsystem to clean the time and depth data of the seabed and base surface of all seismic lines in S1, remove the erroneous data rows generated during Geoframe export, and obtain the correct stratigraphic data.

[0009] S3. Use the test line sorting subsystem to split the correct layer data in S2 one by one according to the test line name and store them in a separate folder named after the test line name.

[0010] S4. Using the formation sediment thickness calculation subsystem, calculate the depth domain sediment thickness of each survey line sorted in S3;

[0011] S5. Use Geocap software and high-precision measured terrain data to determine the latitude and longitude coordinates of the FOS points corresponding to each survey line.

[0012] S6. Using the 1% sediment thickness point calculation subsystem, based on the sediment thickness of each survey line depth domain obtained in S4 and the latitude and longitude coordinates of the corresponding FOS point obtained in S5, collect points that satisfy the condition that the sediment thickness of each point on the survey line is greater than 1% of the distance from the FOS point to that point. These points are the 1% sediment thickness points.

[0013] S7. Based on the data in S6, draw a seabed-base depth map, a sediment thickness map, and a map showing the location of the 1% sediment thickness point to demonstrate the specific locations of the FOS point and the 1% sediment thickness point.

[0014] In some embodiments, the aforementioned method for plotting points representing 1% of the seabed sediment thickness includes, in S3, a single survey line folder containing seabed surface survey line and basal surface survey line data.

[0015] In some embodiments, the aforementioned method for plotting points representing 1% seafloor sediment thickness includes, in step S4, the calculation method comprising:

[0016] S41. Read the stratigraphic data of the seabed and base surface, select continuous stratigraphic data of CDP, or select discontinuous stratigraphic data with a discontinuity of less than 100m and use piecewise Hermite interpolation polynomial to fill in the gaps to ensure the continuity and accuracy of the data.

[0017] S42. Trim the seabed and base surface in S41 so that the seabed and base surface completely overlap and align to obtain a continuous seabed and base surface with consistent length.

[0018] S43. Subtract the seabed surface from the basal surface to obtain the sediment thickness in the time domain;

[0019] S44. Convert the sediment thickness in the time domain to the sediment thickness in the depth domain.

[0020] In some embodiments, in the aforementioned method for plotting seabed sediment thickness points of 1%, if a layer data with a discontinuity greater than 100m appears in S41, it indicates a layer data error, and it is necessary to return to S1 to check the original seismic data in the Geoframe.

[0021] In some embodiments, the aforementioned method for mapping points representing 1% of the seabed sediment thickness, wherein...

[0022] The seabed and base surfaces obtained in S42 were compared with the overlapping portions of the seabed and base surfaces in the Geoframe seismic interpretation software to determine the accuracy of the S42 results.

[0023] In some embodiments, the aforementioned method for plotting 1% sediment thickness points on the seabed, wherein the method for determining the 1% sediment thickness point in S6 includes:

[0024] S61. Read the latitude and longitude coordinates of all FOS points and their corresponding survey line names, and match the FOS point coordinates with the survey lines according to the survey line names;

[0025] S62. Calculate the straight-line distance from the FOS point to each CDP point on the survey line to obtain the first distance;

[0026] S63. Calculate the ratio of the depth domain sediment thickness to the first distance for each CDP point to obtain several first ratios. All points with a first ratio greater than 0.01 are 1% sediment thickness points.

[0027] S64. Export the x-coordinate, y-coordinate, time-domain thickness, depth-domain thickness, CDP number, first distance, first ratio, and index number in the original coordinate column for all 1% sediment thickness points that meet the conditions, and export the 1% sediment thickness point that is farthest from the FOS point.

[0028] In some embodiments, the aforementioned method for plotting points representing 1% of the seabed sediment thickness includes, in step S7, the plotting method comprising:

[0029] S71. Automatically read sediment thickness data, seabed and basal depth data, FOS point coordinates, and 1% sediment thickness points that meet the conditions for all survey lines.

[0030] S72. Calculate the azimuth of the survey line in the direction of increasing CDP;

[0031] Among them, the azimuth angle between 67.5° and -112.5° is the reverse-hand section, which is drawn in descending CDP manner to ensure that the final view is the forward-hand section direction;

[0032] S73. Draw the subplot, which includes four pieces of information: FOS point, 1% sediment thickness point, sediment thickness, and 1% thickness line.

[0033] S74. Draw the following sub-map, which includes information on the depth of the seabed and the depth of the base.

[0034] S75. Draw a planar distribution map of 1% sediment thickness points, including planar distribution information of 1% sediment thickness points.

[0035] The present disclosure provides a method for mapping 1% sediment thickness points on the seabed. First, based on seabed and basal layer data interpreted by Geoframe seismic interpretation software, the exported data is cleaned and sorted to obtain cleaned seismic data for a single seismic line. Then, the seabed and basal surfaces of this seismic line are aligned at both ends, and data missing due to cleaning is interpolated to obtain a completely continuous CDP (Central Depth Map). Next, the time-domain sediment thickness is obtained by subtracting the time-domain depth value of the seabed from the basal surface's time-domain depth value. Then, the time-domain sediment thickness is converted to the depth-domain sediment thickness using a time-depth conversion formula. Combining the latitude and longitude coordinates of FOS (Forward Optical System) points, all points on the seismic line that satisfy the 1% sediment thickness criteria are calculated. Finally, the depth-domain seabed and basal surfaces, along with the sediment thickness, FOS point coordinates, 1% sediment thickness points, and 1% thickness lines, are plotted as a cross-section. The distribution range of the 1% sediment thickness points can be plotted on a plane using QGIS software. This invention, through the interpretation of long-cable seismic profiles, utilizes high-precision time-depth conversion relationships to maximize the accuracy of 1% sediment thickness calculations. Furthermore, it can process multiple seismic data points simultaneously, significantly reducing labor costs under large data volumes and meeting the requirements of Article 76 of the United Nations Convention on the Law of the Sea regarding 1% sediment thickness calculations. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of a method for drawing points representing 1% of the seabed sediment thickness, as disclosed in Embodiment 1 of this disclosure;

[0038] Figure 2 This is a partial location map of a long cable multi-channel seismic survey line in a method for drawing points representing 1% of the seabed sediment thickness disclosed in Embodiment 1 of this disclosure;

[0039] Figure 3 This is a cross-sectional view of the NH2 multichannel seismic survey line in a method for drawing points of 1% seabed sediment thickness disclosed in this embodiment of the present disclosure;

[0040] Figure 4 This is a cross-sectional view of the NH3 multichannel seismic survey line in a method for drawing points of 1% seabed sediment thickness disclosed in this embodiment of the present disclosure;

[0041] Figure 5 This is a diagram showing the calculation results of the continental shelf demarcation related elements of the NH2 survey line in a mapping method for 1% sediment thickness points on the seabed disclosed in this embodiment;

[0042] Figure 6 This is a diagram showing the calculation results of the continental shelf demarcation related elements of the NH3 survey line in a mapping method for 1% sediment thickness points on the seabed disclosed in this embodiment;

[0043] Figure 7 This is a partial plan view of the 1% sediment thickness points that meet the conditions in a multichannel seismic survey line in a drawing method for 1% sediment thickness points on the seabed disclosed in Embodiment 1 of this disclosure;

[0044] Figure 8 This is a schematic diagram of the continental shelf delimitation rules in a method for drawing points representing 1% of the seabed sediment thickness disclosed herein. Detailed Implementation

[0045] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0046] These embodiments are provided to make the disclosure thorough and complete, and to fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0047] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0048] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0049] Example 1

[0050] Reference Appendix Figure 1 , 2 In embodiments 3 and 4, this embodiment discloses a method for mapping points representing 1% of the seabed sediment thickness, which includes: S1, collecting SGY seismic data and importing the SGY seismic data into Geoframe seismic interpretation software for interpretation to obtain time-depth data of the seabed surface and base surface, and exporting the seabed surface and base surface data of all seismic survey lines. In this embodiment, two survey lines are set, namely NH2 and NH3.

[0051] S2. Use the multi-line stratigraphic data cleaning subsystem to export the interpretation stratigraphic data in a specific format. Check all interpretation stratigraphic data, namely the time and depth data of the seabed and the base. Output the correct rows from all data and record the number of correct rows. Delete erroneous rows and count the number of erroneous rows. The final result can be calculated to ensure that the subsequent sorting is based on correct data.

[0052] S3. Using the seismic line sorting subsystem, the cleaned and correct seismic lines are separated one by one and named individually. The time and depth data of the seabed and basal surfaces corresponding to the seismic lines are placed into the corresponding seismic line folders, namely NH2 and NH3 folders. Each individual folder is checked to see if it contains the two stratigraphic files of the seabed and basal surfaces. If any stratigraphic file is not displayed, the program will prompt that the original file needs to be checked again to ensure that no errors have occurred. It is understandable that the seabed and basal surfaces are key factors in determining the final sediment thickness. The farthest 1% sediment thickness point needs to be determined by the relative position of the seabed and basal surfaces, and an accurate profile map needs to be drawn. Therefore, it is necessary to ensure that each seismic line folder contains the two stratigraphic files of the seabed and basal surfaces.

[0053] S4. Using the stratigraphic sediment thickness calculation subsystem requires selecting continuous stratigraphic data from the seabed and basal planes of the CDP (Central Deposition Layer). The data is then cropped to align the positions of the seabed and basal planes within the same CDP. This ensures that the image is continuous and uninterrupted when plotting using this data. When calculating sediment thickness, the sediment thickness in the time domain is obtained by subtracting the seabed thickness from the basal plane thickness. Figure 3 and Figure 4 As shown, the depth-domain sediment thickness is obtained by using the time-depth conversion formula (1) derived from the South China Sea ocean drilling well U1433.

[0054] z = 0.000188295t 2 + 0.695896t(1)

[0055] Where z is the sediment thickness in the depth domain and t is the sediment thickness in the time domain, the depth domain thickness of each survey line is derived.

[0056] S5. Use Geocap software and high-precision measured topographic data to determine the latitude and longitude coordinates of the FOS points for each survey line;

[0057] S6. Using the 1% sediment thickness point calculation subsystem, calculate all 1% sediment thickness points that meet the conditions. First, read the latitude and longitude coordinates of the FOS points for NH2 and NH3 determined in step S5. Calculate whether the ratio of the sediment thickness at each CDP point on the survey line to the straight-line distance from that point to the FOS point (i.e., the first distance) is greater than 0.01. If the first ratio is greater than 0.01, then that point is a 1% sediment thickness point. Export the xy coordinates, time-domain thickness, depth-domain thickness, CDP number, first distance, first ratio, and index number in the original coordinate column for all 1% sediment thickness points that meet the conditions. Also export the 1% sediment thickness point farthest from the FOS point and use it as the basis for plotting. The CDP is: common depthpoint gather.

[0058] S7. Based on the data from S4, S5, and S6, draw a seafloor-base depth map, a sediment thickness map, and a 1% sediment thickness point map to show the specific locations of the 1% sediment thickness points. For details, refer to [reference needed]. Figure 5 , Figure 6 and Figure 7 The azimuth of the survey line is calculated according to the direction of increasing CDP. Azimuths between 67.5° and -112.5° are considered reverse-hand profiles, and the CDP is drawn in descending order to ensure the final view reflects 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...) of the first and last CDPs for each survey line. n ,y n ); 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 angle. From the above sub-figure, we can see the sediment thickness at each CDP on the survey line. The blue inverted triangle marks the location of the FOS point. The short line is the 1% thickness line, which is a line extending from the FOS point to both ends of the survey line with a slope of 0.01. This line can be used as a reference line for whether the 1% sediment thickness point is met. Specifically, the ratio of the sediment thickness value at any point on this line to the first distance to that 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 that CDP, then that point meets the condition of a 1% sediment thickness point, i.e., it is a reference point. Figure 5 and Figure 6 In the upper sub-plot, the red area on the horizontal axis represents the point furthest from the FOS point when determining the continental shelf boundary. This point is used as the outer boundary of the continental shelf. The lower sub-plot provides information on the seabed surface depth and basal depth of NH2 and NH3, respectively. The seabed surface is represented by the lined area, and the basal surface by the filled area. The sediment thickness is zero at the junction of the basal surface and the seabed surface. Therefore, by using the upper and lower sub-plots, we can gain a more comprehensive understanding of various aspects of the survey line and integrate the data. Compared to the traditional method of displaying individual indicators separately and requiring manual comparison and calculation, this method greatly improves the accuracy of the calculation.

[0059] The embodiments of this disclosure have now been described in detail. To avoid obscuring the concept of this disclosure, some details known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0060] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner.

Claims

1. A method for plotting points representing 1% of the thickness of seabed sediments, characterized in that, include: S1. Collect sgy seismic data and import the sgy seismic data into Geoframe seismic interpretation software for interpretation to obtain time-depth data of the seabed and base surface of all seismic survey lines. S2. Use the multi-line stratigraphic data cleaning subsystem to clean the time and depth data of the seabed and base surface of all seismic lines in S1, remove the erroneous data rows generated during Geoframe export, and obtain the correct stratigraphic data. S3. Use the test line sorting subsystem to split the correct layer data described in S2 one by one according to the test line name and store them in a separate folder named after the test line name. S4. Using the formation sediment thickness calculation subsystem, calculate the depth domain sediment thickness of each survey line sorted in S3; S5. Use Geocap software and high-precision measured terrain data to determine the latitude and longitude coordinates of the FOS points corresponding to each survey line. S6. Using the 1% sediment thickness point calculation subsystem, based on the sediment thickness of each survey line depth domain obtained in S4 and the latitude and longitude coordinates of the corresponding FOS point obtained in S5, collect points that satisfy the condition that the sediment thickness of each point on the survey line is greater than 1% of the distance from the FOS point to that point. These points are the 1% sediment thickness points. S7. Based on the data in S6, draw a seabed-base depth map, a sediment thickness map, and a map showing the location of the 1% sediment thickness point to demonstrate the specific locations of the FOS point and the 1% sediment thickness point.

2. The method for mapping points representing 1% thickness of seabed sediments according to claim 1, characterized in that, A single survey line folder in S3 contains seabed surface survey line and base surface survey line data.

3. The method for mapping points representing 1% thickness of seabed sediments according to claim 1, characterized in that, The calculation methods in S4 include: S41. Read the stratigraphic data of the seabed and base surface, select continuous stratigraphic data of CDP, or select discontinuous stratigraphic data with a discontinuity of less than 100m and use piecewise Hermite interpolation polynomial to fill in the gaps to ensure the continuity and accuracy of the data. S42. Trim the seabed and base surface in S41 so that the seabed and base surface completely overlap and align to obtain a continuous seabed and base surface with consistent length. S43. Subtract the seabed surface from the basal surface to obtain the sediment thickness in the time domain; S44. Using the time-depth conversion formula (1) of ocean drilling constraints, the sediment thickness in the time domain is converted into the sediment thickness in the depth domain. 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.

4. The method for mapping points representing 1% thickness of seabed sediments according to claim 3, characterized in that, If there are layer data with discontinuities greater than 100m in S41, it indicates a layer data error. You need to return to S1 and check the original seismic data in the Geoframe.

5. The method for mapping points representing 1% thickness of seabed sediments according to claim 3, characterized in that, The seabed and base surfaces obtained in S42 were compared with the overlapping portions of the seabed and base surfaces in the Geoframe seismic interpretation software to determine the accuracy of the S42 results.

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

7. The method for mapping points representing 1% thickness of seabed sediments according to claim 1, characterized in that, The drawing methods in S7 include: S71. Automatically read sediment thickness data, seabed and basal depth data, FOS point coordinates, and 1% sediment thickness points that meet the conditions for all survey lines. S72. Calculate the azimuth of the survey line in the direction of increasing CDP; Among them, the azimuth angle between 67.5° and -112.5° is the reverse-hand section, which is drawn in descending CDP manner to ensure that the final view is the forward-hand section direction; S73. Draw the subplot, which includes four pieces of information: FOS point, 1% sediment thickness point, sediment thickness, and 1% thickness line. S74. Draw the following sub-map, which includes information on the depth of the seabed and the depth of the base. S75. Draw a planar distribution map of 1% sediment thickness points, including planar distribution information of 1% sediment thickness points.

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