Supported Seismic Formats

SEG-Y and VDS Formats

When working with SEG-Y seismic data in the Ground Model Add-in, one of the initial steps is to convert the file(s) from SEG-Y to VDS format.

The SEG-Y format was developed in the early -70s and designed for analog tape storage. The VDS format, on the other hand, is a format that originates in the gaming industry and is much better suited for compression and cloud storage. It is also adopted by the OSDU-consortium (read more here).

Unfortunately, the SEG-Y format is commonly not straightforward to work with and a certain degree of knowledge is required to understand what to look for.

The SEG-Y scanner embedded in the Ground Model Add-in is a powerful and comprehensive tool that will let you inspect SEG-Y files in detail and enable the user to find the correct input parameters and settings for SEG-Y to VDS import/conversion.

ZGY/Open ZGY Format

Ground model supports the ZGY/Open ZGY seismic 3D format directly, so conversion from ZGY to VDS is not required nor possible. This means that step 1. below (Importing Seismic) in this case is skipped.

Importing Seismic

There are three steps required to import your SEG-Y seismic data into the Ground Model Add-in:

1. Converting the SEG-Y data to the VDS format

2. Creating an empty feature class to which the VDS/ZGY seismic will be linked

3. Linking the VDS/ZGY seismic to the feature class above

When these steps have been performed, the feature class will contain the seismic navigation as well as links to the VDS files (amplitudes will be read from here). The steps above can be performed with both 2D and 3D data.

Converting SEG-Y Seismic to VDS

Click SEG-Y to VDS in the pulldown menu under Seismic Import on the Ground Model Toolbar. This will open a dialog pane where the SEG-Y file(s) and the output location are selected. Both input and output files can be stored locally, on a shared drive or in the cloud. If working with cloud storage, use cloud browser to select input/output locations (see Cloud Support). After conversion, the VDS files created will be given the same name(s) as the SEG-Y input file(s) except for the file extension.

In the Parameters section, select the Dimension (2D or 3D seismic). Sample Interval will be filled in automatically based on the selected seismic. However, sample Interval Unit (milliseconds, meter or feet) needs to be selected. The Compression Method should be selected according to user requirements (see recommendations here). If the file has been written previously and already exists the default setting is to overwrite this. Optionally, it is possible to rename, skip or cancel instead. Spatial Reference (CRS) needs to be entered. The CRS is often stated in the SEG-Y file header. This can be displayed in the File Headers Tab in the SEG-Y Scanner. If it is not included there, this information could be available for example in a processing report or other documentation accompanying the data.  

When converting SEG-Y files to VDS the following Header Fields information is required:

1. X and Y Position

2. Ensamble Number

3. Energy Source Point Number/Shot Point

4. Vertical Offset

Header Fields

Clicking the Analyze button in the Header fields section will run a scan through the selected file and will, based on byte position values, suggest byte positions for the parameters below automatically. In most cases this should work. However, there is not a guarantee that correct byte positions are selected, and it is recommended to check the result in the SEG-Y Scanner .

X and Y position

VDS uses the X and Y coordinates to create the geometry. Ensure that the X and Y fields header values point to valid X, Y coordinate fields in the headers. By default, Ground Model uses Ensamble X/Y in byte positions 181 and 185 for X and Y coordinates. In the SEG-Y scanner, browse in the file and check that the values in these byte positions look reasonable. This is done by opening the trace header tab, ticking off the correct byte positions and inspect the values in detail in the trace table (tab). If the values here seem to be scaled, check if the coordinate scalar in byte position 71 is correct (will be applied automatically during conversion). Optionally, this coordinate scalar can be overridden by a manually entered value both in the scanner and during conversion. Please note that the values in the Trace Table in the scanner will be scaled with the coordinate scalar in byte position 71 if the apply scalars is ticked off. If the byte positions for Ensamble x and Y coordinates cannot be used, check byte positions 73 and 77 to see if Source X and Y Coordinates could be used instead. In the header statistics tab, the file can be scanned to check for irregularities in terms of coordinates for first and last traces, Navigation extent and values equal to 0.

As a final test of navigation and settings before import/conversion, it is possible to preview the file navigation in the map. The basic workflow in the scanner follows the tabs from left to right and functionality in the tabs to the right might require input in the tabs to the left. In the case of the navigation preview it is dependent on correct X/Y and CRS input in the Coordinate Settings in the Trace Headers Tab.

Ensamble Number

The next step is to check that the Ensamble number, in byte position 21, has a value with an incremental step of 1 throughout the file. By default, Ground Model reads this value from position 21. However, this numbering is usually also read from position 1, 5, 9, 13, 17. Irregularities in consecutive trace numbering will be identified below the coordinate information when scanning the file under the Header Statistics tab in the SEG-Y Scanner.

Energy Source Point Number/Shot Point

The energy source point number, also known as shot point, is required when converting SEG-Y files to VDS format. By default, the SEG-Y to VDS process in Ground Model uses byte position 17 for this value. As with the ensamble number, this is also normally a value that has an incremental step of 1 from trace to trace throughout the file. However, although this input is required, it is only used for metadata purposes. Therefore, the VDS file will be generated even though an incorrect byte position for Energy Source Point is used.

Vertical Offset

The last thing to check before converting SEG-Y files to VDS is the vertical offset, normally the Delay Rec Time in byte position 109. This may or may not contain values. When dealing with SBP-data it often does. By default Ground Model takes the vertical offset in to account when generating VDS files, meaning it will apply the values in Delay Rec Time Byte Position 109 (or any other position specified by the user) and potential values in the Time Scalar Byte Position 215.   In the Samples tab in the SEG-Y scanner the samples can be loaded. In the Coordinates tab, it is possible to apply delay recording time with none, a constant or a value in a selected byte position (109 by default) as input, as well as specifying a time scalar, either constant or byte position, if any.

Advanced

Under the Advanced section the following entries may be inserted or edited:

1. Level of detail (LOD): Store lower-resolution copies of the bulk data. Each lower-resolution level has half the number of samples in each axis direction, so for 3D data a lower resolution level has 1/8th the number of samples as the previous resolution level. An increased LOD number will increase file size slightly, but improve visualization performance. For archiving use level 0 which is full resolution without lod levels.

2. Coordinate Scalar Override: If Coordinate Scalar Override (floating point) is given, it is used to scale the coordinates in the header instead of determining the scale factor from the coordinate scale trace header field (byte position 71). If unchecked or 0, scalar from trace header will be used. Otherwise plain mathematical multiplication of the actual value will be applied.

3. Delay Rec Time Scalar: The time scalar in Byte Position 215 will by default be used to scale the delay rec time. If the value in the byte position is incorrect, a time scalar can be entered and activated manually to override this.

4. Convert from seconds of arc: If the value in byteposition 89 (Coordinate units) is 2, this means the coordinates are given in seconds of arc (deprecated). If this byte position is not used although the file is actually given in seconds of arc, or incorrectly filled in, this field should be checked off to convert the resulting VDS file from seconds of arc.

5. Ignore Warnings:

6. Generate Ensamble Number: If no byte position has a value with an incremental step of 1 throughout the file, this option can be ticked off to generate a consecutive trace numbering.

Clicking the import button will generate the sesimic VDS file(s). Multiple files (e.g. from the same seismic survey) can be generated at a time as long as the input settings are the same. The files will be processed in the background in batches of 10. During processing the user can perfom other tasks in Ground Model/ArcGIS Pro. Processing progress can be viewed in the Job Monitor under the Ground Model Messages pane.

Creating Seismic Feature Class

The second step is to create an empty target feature class using the Create Seismic Feature Class tool found in the pull down menu under the Seismic Import button on the Ground Model tool bar.

Reading Seismic to Feature Class

VDS 2D to Features under the Seismic Import pulldown menu will open a dialog pane where your VDS 2D seismic can be imported to the feature class you created in the step above. If your seismic is 3D (VDS or ZGY), use Seismic Volume to Features instead.

To see the seismic data go to the section: Visualizing data