svchapter03 loading seg y data

Chapter 3: Loading 2D and 3D SEG-Y Data

Chapter 3

Loading 2D and 3D SEG-Y Data

The first step in creating a seismic interpretation is generally to convert SEG-Y data to .2ds (for 2D data) and/or .3ds (for 3D data) format that can be used in SeisVision. The 2D or 3D SEG-Y Load Wizard in SeisVision progresses through a series of steps that require all the pertinent information to correctly load data. The resultant .2ds/.3ds files can be stored at any location on an individual computer or in the network environment during data loading. It is, therefore, not required to create a project in ProjectExplorer prior to loading SEG-Y data. It may, however, be desireable to create a project before SEG-Y data loading because certain default settings (map coordinates, units, etc.) may then be used without worry of inserting the wrong value.

In Chapter 2 a project, Moosehead, was created in ProjectExplorer. The Moosehead project has both 2D and 3D seismic data available in SEG-Y format. SeisVision has two SEG-Y load wizards, one for 2D and one for 3D data, to assist you with loading the seismic data.

In this chapter you will learn to:

Load 2D and 3D SEG-Y seismic data

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Loading 2D SEG-Y Data The 2D SEG-Y Load Wizard is used to load a 2D SEG-Y file from tape or disk. SeisVision reformats the SEG-Y file data and saves the data to a SeisVision 2D seismic file (.2ds). The 2D seismic file will be attached to a SeisVision interpretation project later. In preparation for any loading exercise, a completed SEG-Y Load Sheet should be available with information for each survey. Information needed on the SEG-Y load sheet to load SEG-Y data is generally available on the Contractor Data Specifications supplied with the seismic survey.

1. Activate SeisVision by clicking on the SeisVision window.

SeisVision will appear with the active project Moosehead displayed in the title bar.

2. Select Load Seismic >> Load 2D Data from the menu bar in SeisVision to launch the 2D SEG-Y Load Wizard.

3. In the 2D SEG-Y Load Wizard – Step 1 of 5, click the Browse button to open the Select SEG-Y Files dialog box.

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4. Click the down arrow in the Look in list box to find the Moosehead SEG-Y files for import. The path is C:\Class Data\SeisVision\Moosehead\Seismic\Segy\2D.

5. Highlight all four SEG-Y files. Select the first one then hold down the Shift key and select the last one so that they are all highlighted as shown below.

6. As long as all SEG-Y files in the directory are in the same format, they can all be converted to 2ds format during the same file loading process. Move all SEG-Y files to the List of Selections list

box using the double left-arrow button.

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7. Click Accept to return to Step 1 of the 2D SEG-Y Load Wizard. For Input Device, select Disk File. If SEG-Y data are stored on tape, the Tape-to-Disk option allows the transfer of data to disk before import.

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8. Click Next to advance to Step 2.

9. The 2D SEG-Y Load Wizard scans the header information to obtain the numbers shown on the Step 2 dialog box. In the SEG-Y Line Header group box on the right side of Step 2, confirm the following values: Number of Samples/Trace is set to 1000 Units is set to Microseconds The Byte Swap Input SEG-Y File checkbox is checked

10. In the Dataset Time Window group box on the right side of the Step 2 dialog box, type the following values: Set the Actual Start Time of Input (in ms) to 0 Set the Start Time of Output (ms) to 0

11. On the left side of the Step 2 dialog box, ensure that the following options are selected: Data Domain is set to Time Data Type set to Amplitude

12. Click the Character Header button on the left side of the Step 2 dialog box to open the SEG-Y Character Line Header dialog box.

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13. The SEG-Y Character Line Header dialog box lists the location of data in the SEG–Y file. Note the position of the 2D Shot, 2D CMP (common midpoint), 2D X Location and 2D Y Location. This information will be entered in the next step. Click Close to return to Step 2, then click Next to advance to Step 3 of the 2D SEG-Y Load Wizard.

14. Use Step 3 of the 2D SEG-Y Load Wizard to enter trace header location information. This information is usually available on Contractor Data Specification Sheets if it is not listed in the Character Header. The Character Line Header box can be used to determine the data locations. It is best to have the SEG-Y Load Sheets (located in the back of this manual) completed with the appropriate parameters. Enter the following information obtained from the Character Header in Step 15 so the Trace Header Locations group box looks like the example shown below:

CMP - Set Start Byte to 21, No. Bytes to 4 Shot # - Set Start Byte to 17, No. Bytes to 4 X Coordinate – Set Start Byte to 81, No. Bytes to 4 Y Coordinate – Set Start Byte to 85, No. Bytes to 4

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15. Click Next to advance to Step 4 of the 2D SEG-Y Load Wizard.

16. Use Step 4 of the SEG-Y Load Wizard to name the lines and set the data projection. The Title Information radio button choices are:

Select Line Name and Version from character header – Opens the Select Line Name Location dialog box to assign line names by highlighting appropriate part of line header.

Select Line Name from character header – Use one Version for all lines – Opens the Select Line Name and Version Selection dialog box to assign the line name and version by highlighting appropriate parts of the character header.

Create Line Name and Version Table – Opens the Create Line Name and Version Table dialog box. Use this dialog box to modify the line name and /or version for each file in the SEG-Y file directory.

Auto create Line Name – Use one Version for all lines – Opens the Auto Create Line Name dialog box. This option will create line names based on a user-defined numerical value.

Select the Create Line Name and Version Table option to open the Create Line Name and Version Table dialog box.

17. The Create Line Name and Version Table can be used to refine the Line Name and Version during import. In the example above for the Moosehead 2D data the default names are correct. Click OK to return to Step 4 of the 2D SEG-Y Load Wizard.

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18. The Output Coordinate System Information group box displays the project’s Map Display Coordinate System as the default coordinates. If the Map Display Coordinate System were different or if the SEG-Y import were being conducted through a different project, the coordinate system could be reset here. In this example the default settings for the coordinate system are correct. Click Next to advance to Step 5 of the 2D SEG-Y Load Wizard.

19. In the Output Directory list box, click the Browse button and path to the Desktop to make it easy to find the files later.

20. Click OK to return to Step 5 of the 2D SEG-Y Load Wizard. In the Output 2ds File Information group box, the four radio button options for naming the output files are:

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Output Filename same as Line Name – The assigned file name will be the same as the Line Name with a numerical increment.

Append Line Name and Version – The assigned file name will include the Version as well as the Line Name.

Same Name as SEGY file – Uses the same Name as the SEG-Y file with a 2Ds extension

Append Line Name and SEGY – The assigned filename will include the SEG-Y file name as well as the Line Name.

Select the Append Line Name and Version option.

21. In the Scaling group box, the five radio button options are:

None – SeisVision preserves the amplitudes of the SEG-Y data set

RMS – SeisVision will perform trace scaling by calculating line sample Root Mean Squared trace amplitude.

Maximum – SeisVision will perform trace scaling by calculating live sample Maximum trace absolute amplitude.

Median – SeisVision will perform trace scaling by calculating live sample Median (middle sorted) trace absolute amplitude.

Mean – SeisVision will perform trace scaling by calculating line sample Mean (average) trace absolute amplitude.

Accept the None default option.

22. Click Load to output Moosehead 2ds files to the project directory. A Successful Load dialog box will appear when the 2ds files have been successfully loaded. Click OK to close the Successful Load dialog box. The 2ds files will be attached to a seismic interpretation in a later task.

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23. Click Finish to close the 2d SEG-Y Load Wizard.

Loading 3D SEG-Y Data

The 3D SEG-Y Load Wizard is used to load 3D SEG-Y data from tape or disk. SeisVision reformats the SEG-Y file data and saves the data to a SeisVision file in .3dx format. The 3dx seismic file will be attached to a seismic interpretation for the Moosehead project later. In preparation for any loading exercise, a completed SEG-Y Load Sheet (found at the back of this manual) based on the Contractor Data Specifications sheet for each 3D survey should be available.

1. If necessary, activate SeisVision by clicking on the icon at the bottom of the screen. From the menu bar in SeisVision select Load Seismic >> Load 3D Data. This menu is only available if no interpretation is active in the SeisVision window.

2. Step 1 of the 3D SEG-Y Load Wizard appears. In the Title Information group box, enter the following values:

For Dataset Name, enter Moosehead3D For Version, enter Original For Location, enter Alberta, Canada For Organization, enter your company name

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3. In the Input SEG-Y File group box, for Input Device, accept the default Disk File. For Input SEG-Y File, use the Browse button ( ) to locate the Moosehead3D.sgy file. The path is C:\ Class Data\ SeisVision\ Moosehead\ Seismic\ Segy\3D

4. Highlight the Moosehead3D.sgy file and click Open.

5. Click Next to advance to 3D SEG-Y Load Wizard - Step 2 of 6. SeisVision extracts line header data from the SEG-Y file.

6. In the SEG-Y Line Header group box, confirm the following values:

Number of Samples/Trace is 1002

Sample Interval (Microsecs) is 2000

Units are Microseconds

Sample Format is IBM 4 Byte Float

The Byte Swap Input SEG-Y File checkbox is checked.

7. The SEG-Y data is a time volume, so ensure that Time is selected in the Data Domain group box and that Amplitude is selected in the Data Type drop-down list box on the left side of Step 2 of the 3D SEG-Y Load Wizard.

Accept the defaults in the Dataset Time Window group box on the right side of Step 2.

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8. Click the Character Header button on the left side of Step 2 of the 3D SEG-Y Load Wizard to open the SEG-Y Character Line Header dialog box. The information displayed describes the Moosehead3D data set, from which most of the Seismic Load Sheet parameters were obtained. Specifically note the 3D Inline bin numbers (9 through 12), the 3D Crossline bin numbers (13 through 16), the 3D X Coordinate (73 through 76), and 3D Y Coordinate (77 through 80). This information will be needed in Step 3 of the 3D SEG-Y loading process.

9. Click Close to return to Step 2 of 6.


11. In Step 3, enter the Inline and Crossline trace header and X and Y Coordinate bin locations obtained from the Character Line Header dialog viewed previously. Because no SEG-Y standard exists for such information, it must be entered manually. The information should alternatively be available from your Contractor Data Specification sheet, if it is not listed in the Character Line Header information. Enter the following information obtained from the Character Header in Step 3 so the Trace Header Locations group box looks like the example shown below:

Inline Bin Number - Set Start Byte to 9, No. Bytes to 4

Crossline Bin Number – Set Start Byte to 13, No. Bytes to 4

X Coordinate – Set Start Byte to 73, No. Bytes to 4

Y Coordinate – Set Start Byte to 77, No. Bytes to 4

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13. In the Grid Information group box, verify that the value in the Increment list boxes for Inlines and Crosslines is 1.

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14. To scan the data set, click the Scan button. The Scan SEG-Y Seismic Dataset dialog box appears with a progress bar monitoring the data scan. Notice that the values in the various boxes in the Scan Information group box change as the data is scanned. The value in the Traces Scanned box also changes during the data scan.

Note: SeisVision scans the data set to extract survey grid information, including the number of the first Inline, the total number of Inlines and Crosslines, and survey origin information. Additionally, SeisVision calculates the survey inclination. A message informs you of the scan progress. After scanning the dataset, the SEG-Y Load Wizard returns to Step 4. SeisVision enters the information it gathers into the Grid Information and Survey Location Information group boxes.

15. Following the scan, the fields for the survey grid information are filled out. Make sure the Units are set to Meters in the Survey Location Information group box.

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16. Click the Coordinate System button. The Select Coordinate System dialog box opens. The coordinate system defaults to the Discovery project’s Map Display Coordinate System. If the SEG-Y data is in some other coordinate system, it must be changed in this dialog box. It is highly recommended that the Discovery project be created with the same map display coordinate system as is the 3D SEG-Y coordinate system to minimize the survey distortion.

17. Accept the default projection parameters and click OK to return to Step 4 of 6 of the 3D SEG-Y Load Wizard.

18. On the Step 4 of 6 of the 3D SEG-Y Load Wizard dialog box, click the Datum button.

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19. For Datum enter 500 Meters, then click OK to return to Step 4 of 6 of the 3D SEG-Y Load Wizard.

20. Click Next to advance to Step 5 of 6 of the 3D SEG-Y Load Wizard.

21. This step provides an opportunity to visually inspect the 3D survey grid SeisVision has extracted from the SEG-Y file before loading it into the 3D seismic file. Confirm that your illustration matches the illustration in Step 20 and click Next to advance to Step 6 of the 3D SEG-Y Load Wizard.

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22. Step 6 specifies file information for the output file. The Output Format, Scaling, and Tile Size of the output data volume can be specified in this dialog box. Refer to the SeisVision Help system for more information on these parameters.

23. In the SeisVision Output File group box, click the Browse button next to Filename.

24. When the Save As dialog box appears, for Save In, select the Desktop. For File name, enter Moosehead.3dx, and then click the Save button to return to Step 6 of the 3D SEG-Y Load Wizard.

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25. Click Load on the left side of Step 6 of 6 and the Load SEG-Y Seismic Dataset progress box appears.

26. A progress bar monitors the data loading process. When the loading process is complete, SeisVision returns to Step 6 of the 3D SEG-Y Load Wizard. The 3D seismic file created can be attached to any SeisVision interpretation project that needs access to the Moosehead.3dx data file.

27. Click Finished to close the 3D SEG-Y Load Wizard.

28. Leave SeisVision open for the next chapter.

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