4.3.11.1.1 SEG-Y Wizard

Generic Import SEG-Y Data wizard can be accessed by clicking on icon in the toolbar of main OpendTect window. The wizard supports import of 2D and 3D prestack and poststack data from one or multiple SEG-Y files. The layout of this window dynamically changes depending on the user choice of Data type.

The generic wizard also supports import of zero-offset VSP data.

Data specific wizards are available via Survey > Import > Seismics > SEG-Y. The layouts are fixed for the data type selected via the menu (Data type option isn't available in these cases).

Input file(s): Select a SEG-Y file to import. In case of importing multiple 2D or 3D SEG-Y files select any of them first and then use the wildcard *.

Import 3D pre- or poststack data from multiple SEG-Y files: files must contain consecutive blocks of inlines and be indexed as filename_1.sgy, filename_2.sgy...

  1. Select one of the files;
  2. replace the file index by a wildcard * in the input field: filepath/filename_*.sgy

Import multiple 2D lines with pre- or poststack data: files must contain individual 2D lines and be indexed with the respective line names as filename_linename1.sgy, filename_linename2.sgy...

  1. Select one of the files;
  2. replace the line name by a wildcard * in the input field: filepath/filename_*.sgy;
  3. those parts of file names replaced by * are used as 2D line names (press Next and see that Line name option is greyed out and set to *).

Edit: (optionally) edit text, binary and trace headers of a SEG-Y file in Manipulate SEG-Y File window.

Data Type: the choice is only available in the generic Import SEG-Y Data window.

Coordinate System: When setting up a new project using a SEG-Y file, use this option to set the Coordinate Reference System for the project whilst importing the data.

Table: information required to import a SEG-Y file (therefore the table layout depends on the data type).

SEG-Y Revision (default = byte 301 of binary header): please refer to SEG standards for details.

Data format (default = byte 25 of binary header): (optionally) overrule data format.

Most header values and data samples are written using several bytes for each word/sample. Therefore knowing a correct byte order is a necessity. All SEG-Y standards (Rev. 0, 1 and 2) require using big-endian byte order. Occasionally one can run into data written using little-endian (reverse) one. Using standard SEG-Y data formats for reading such data results in unexpected scanned values of trace headers and unexpectedly large sample values (check the histogram). In this case use data formats with (byte swapped) option.

Number of samples (default = byte 21 of binary header / byte 115 of trace header): (optionally) overrule the number of samples per trace.

Z Range (units = seconds or meters).

OpendTect doesn't support import of a SEG-Y file with varying trace lengths (i.e. Z range start and interval must be constant for all traces in a file).

Data positioning:

Rev.1/Rev.2: trace header byte locations are standard, i.e. can't be selected by a user. If the file is wrongly tagged as Rev.1/Rev.2, over-rule it as 0 in Actually use column in order to be able to select non-standard trace header bytes.

3D poststack data is loaded based either on Inline/Crossline numbers or X/Y coordinates (see below Use I/C and Use (X,Y) options).

 

Rev.0 defaults

Rev.1/Rev.2 hard-coded standard bytes
In-line range 9 189
Cross-line range 21 193
X-Coordinate range 73 181
Y-Coordinate range 77 185
Offset range (prestack only) 37 37

2D poststack data is loaded based on trace numbers, reference numbers (SP) and X/Y coordinates.

 

Rev.0 defaults

Rev.1/Rev.2 hard-coded standard bytes
Trace number range 5 5 (can be over-ruled)
Shot-Point number range 197 197
X-Coordinate range 73 181
Y-Coordinate range 77 185
Offset range (prestack only) 37 37

Trace number must be unique for each trace along the line, therefore it can be either sequential trace number (byte 5) or CDP trace number (byte 21). A user is always allowed to select a non-standard byte even when the file is Rev.1.

2D and 3D prestack data additionally requires offset information.

Store this setup: save a SEG-Y import setup at the survey data root level.

Use saved SEG-Y setup: retrieve one of the stored setups.

Scan the entire input: updates Quick scan result with Full scan result of the entire input file.

Examine input file: opens SEG-Y Examiner window for a specified Number of traces to examine (default=1000 traces).

(default = empty): (optionally) enter XY scalar to ignore scalco (byte 71 of trace header). X/Y coordinates are multiplied by this factor.

Note that scalco is the scale factor for all coordinate bytes with value plus or minus 10 to the power 0, 1, 2, 3, or 4 (if positive, multiply, if negative divide).

Histogram: displays a distribution of amplitudes after Quick (partial) or Full scan.

Data specific options:

3D (pre- and poststack) data positioning can be based either on Inline/Crossline or X/Y coordinates of each trace:

2D (pre- and poststack) data Z-range can vary per SEG-Y file if multiple lines of different vintages are imported at the same time:

Overruling of Z Range start/interval and Number of samples is possible only if File Z's is unchecked.