OpendTect User Documentation version 4.2
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Chapter 3. How to...

Table of Contents

3.1. Quickstart a Project.
3.2. Display loaded data
3.3. Interpret horizons
3.4. Interpret Faults

3.1. Quickstart a Project.

OpendTect is a seismic attribute processing, visualization and interpretation system.

The primary input is:

A 3D seismic data volume or 2D seismic data that are imported via SEG-Y.

The primary outputs are:

A 3D volume/2D linesets, such as a filtered cube/linesets or any other type of cube/lineset produced by the system. Seismic data are exported via SEG-Y.
Interpretations horizon/faults.

OpendTect Projects are associated with a seismic survey. The first time OpendTect is started, the user must define a new survey and import seismic data. At subsequent start-ups, OpendTect will start-up in the survey that was active when the program was closed. The user may select another, pre-defined survey using Survey > Select/Setup and browsing to its location using Set data root.

Define a new survey. Select the Select/Setup option under the Survey menu or click on the survey icon

. Specify the name, ranges and the relationship between inline / crossline and X / Y co-ordinates in the survey parameter window. You can enter the survey geometry manually or by scanning a segy file. After scanning, you can still adjust all parameters. The notes area can be used for free format information (e.g: Type of Survey, Client Company, Contact Person, etc ...).

Optionally, a data access module can be purchased at dGB that gives access to Seisworks/OpenWorks (Landmark) or GeoFrame (GeoQuest IESX). The core of this module is developed by UK-based software providers ARK CLS and is known as Ideal Toolkit (ITK). The license gives you access to the data store of your choice. It currently supports I/O of survey parameter, seismic data, horizons, and well data.

Import seismic data. Select Import-SEGY from the Survey menu and specify the input parameters. In case you do not know the parameters, use the "Examine" utility to dump the EBCIDIC header, the binary header and the first 100 traces header. From these it should be possible to determine the few input parameters needed by the program. The internal OpendTect format is 8,16 or 32-bit depending on whether the input Cube was 8, 16 or 32 bit.

Generating seismic attributes. Now, you are almost ready to go! You have created a survey, which contains at least one seismic volume. To do some real work, you must also create one or more attributes in the attribute engine that reveal relevant, useful seismic information. Several default attribute sets are available to get you started quickly. Open the attribute engine Processing/Attributes (or press the "Edit attributes" icon) and press the button

to open a default attribute set. You are asked to select the input data to complete the attribute definitions. Press "OK" to save the attribute set, this will bring you back to the main window.

Display your data or attributes. Now you are ready to display any of the defined attributes, anywhere in the volume. Create, for example, an inline element by right-clicking on inline in the tree and pressing Add. Go into interact mode (press

). Position the element in the middle of the cube by using the arrows along the side of the element. When positioned, click anywhere in the black area (outside the element) and select in the data selection window that automatically pops up the data you wish to view on this element. You can either select from a stored volume or you select one of the defined attributes. If you choose an attribute, then this attribute will be calculated on-the-fly at all sample positions of the displayed element.
Note: The time of displaying an attribute is much longer than the time of displaying a stored volume. That is why it is always better to store your attribute(s) as stored volume or stored surface data.

You can also find tutorial videos on the OpendTect's website, which will guide in steps to start a new project.

The next part will briefly describe how to setup a project.

3.1.1. OpendTect Survey

The OpendTect Surveys are organized under Survey selection window which is used to change, create, edit or remove the survey(s). It is launched from Survey (menu) > Select/Setup or select survey icon

.

The Survey selection window is divided into three panels with some key buttons. The left panel shows the already existing surveys in the present root directory. The root (location) directory of OpendTect survey can be changed by pressing the Set Data Root... button. The right panel shows the map view of selected/loaded survey. It is helpful to QC the survey orientation (true north display). The bottom panel is basically used to put important notes about the project (Type of Project, Client Company, Contact Person etc ...).

For more further information about this window, please go to Survey selection window.

3.1.2. Setup 2D/3D survey

To setup a new Survey (2D/3D) press New button in the survey selection window. The Survey setup window will pop up (see below) in which the survey parameters are specified.
It may be noted that the survey is setup to define the survey box. The key parameters are survey type and its respective coordinates. That can be entered either manually or by scanning a SEGY file. Optionally, in case you have workstation access, you can get them from GeoFrame as well. Or if the OpendTect survey already exists, copy the coordinates by pointing the other survey.

Note: In OpendTect, everything is tied to a 3D (X,Y,Z) with inline/crossline coordinate system. This is regardless of whether you have 3D data at all. Thus, for a survey which contains only 2D lines, a fake 3D survey box of inline/crossline system is needed. But on the other hand, if you want to use both 3D and 2D data, set up the survey according to the 3D cube.

3.1.2.1. Survey name and Type

The top most panel of the survey setup window defines two important things along with its disk location. The Survey directory name is entered in the first field. A directory with this name would be created in the root where you will save the OpendTect survey. The field for Full Survey name is filled with proper name of the survey that will be seen later on in the OpendTect survey selection window. It is recommended that survey name and its directory name should be same as shown in previous figure of survey setup but different names can also be used without any problem. In third field select the location on disk where you want to save this survey.
The most important thing is the Survey type which can be Only 3D, Both 2D and 3D or Only 2D. The type is set accordingly:

Only 3D is used when the survey contains only 3D cube(s).
Both 2D and 3D is set when survey contains both 3D cube(s) and 2D line(s).
Only 2D is set when survey contains only 2D line(s). And recalling the above note again: A fake inline/crossline system is defined to setup such survey regardless that 3D cube is not there.

3.1.2.2. Survey ranges

In the second panel of survey setup window the fields for Inline, Crossline and Z-ranges are filled with following possible ways:

Filling the ranges by scanning a SEG-Y file: Set the Survey ranges into Scan SEG-Y File(s) ->>. The SEG-Y import window will pop up. In this window, select the input file/volume and press OK to start scanning the input file. After the scan is completed, the survey ranges will be filled automatically.
Entering Manually: If you already know the extents of survey ranges (Inline/Crossline/Z-range), just fill the maximum and minimum ranges and corresponding steps.

For 2D only: Set the Survey ranges into Set for 2D only ->> and press GO... The window will pop up (as shown below) in which the average trace distance and the ranges for XY-coordinates are entered; Fill the approximate values and press OK afterward. These parameters are survey characteristics to define the survey box. In the survey ranges the fake ranges for inline, crossline are automatically set. Then fill in the Z range (no precision needed; 2D lines can stick out of the display box in all directions). The limit of the survey box will not affect the loading of 2D lines. The lines outside the survey area would be loaded normally. And that should be it. Press OK and select the new survey.

Get from GeoFrame: This option is used if you have workstation access to get the survey ranges from a GeoFrame project.

Copy from other Survey: Additionally, if the survey already exists, you can copy the ranges from that OpendTect survey.

3.1.2.3. Coordinate Settings

The relationship between inline/crossline and X/Y is setup generally by using this panel. The coordinates are automatically setup after scanning the SEG-Y file. You will only fill them if you are inserting survey ranges manually. Nevertheless, the three point (easy) method is not accurate because of rounding off errors which may not be 100% accurate. Both methods have been described here.

In Easy mode, the coordinates are transformed by using three known points. Under Coordinate settings panel of Survey setup window, fill the inline and crossline and corresponding known XY-transformation as shown in figure of previous section.
In Advanced mode, the XY coordinates are calculated by using an equation shown below. The inputs required from user are origin (X,Y) and inline/crossline intervals along X/Y directions respectively. By checking the Overrule easy settings, the current easy settings would be overwritten.

** The required inputs include origin X,Y pair, inline and crossline interval in both X & Y directions.

3.1.3. Data loading

The data loading has been briefly addressed in two sections. The first section will guide in loading the 2D/3D SEG-Y data, while the second will guide in loading well data.
The details of each section will be described in Import Seismic chapter.

3.1.3.1. Load Seismic (2D/3D)

The loading of SEG-Y data is done via Import sub menu under survey main menu (Survey > Import > Seismic > SEG-Y...)
To start loading of 3D SEG-Y Volume, follow the steps:

Go to Survey >Import > Seismic >SEG-Y... In SEGY Tool window choose File type: 3D Volume to import the SEG-Y data.
In the Input SEGY field, select and locate the input segy file.
Set check to the Multiple files to import more segy files. Write the number of files in the first text field and number of steps (e.g. Vol-1, Vol-2, Vol-3, ... Vol-n). Where 'n' is number.
Select the input file type: 2D/3D-Pre or Poststack data.
Select the number of traces that will be examined to display the trace header information.
Optionally, if you want to overrule the number of samples, set check to this field and fill the correct number of samples.
Select an appropriate SEG-Y file format.
If the bytes in a header have to be swapped, it can be set here.
Press Ok to proceed further
The SEG-Y Scan and SEG-Y Examiner window will launch in next step. Fill the appropriate byte locations in the SEG-Y scan window. Write the output cube name and press OK to start loading the segy file.

3.1.3.2. Load Well data

In OpendTect, the well data has been organized into four (4) sub categories: Well tracks, Logs, TD Models and Markers. Each category is either loaded via Survey > Import menu or Well manager. In this section, we will cover how to load/setup a complete well in OpendTect.

Load Well track and Time to depth Model (via Import): To load a well track, go to the main menu bar and select Survey - Import - Well - Ascii - Track. The Import Well Track window will be launched. In the Well Track file field select the input well track file. The Well track file should contain three main columns i.e. X, Y, TVDSS (True Vertical Depth Sub Surface) and optional MD (Measure Depth) column. The file header can be defined in this window. Click the Examine button to view the input file before loading, and to determine the header type. See Import - Well section to learn how to set the file headers (fixed size/variable). The format definition is used to specify the columns (XYZ) definition and unit system of the input ASCII file. Optionally, a vertical well can also be defined if the file doesn't exist. This is done by setting uncheck to Well Track File field. In this case, specify the XY coordinates and depth range (default meters).

In the depth to time model field, locate and select the appropriate time-depth file. Specify the file header and format definitions. If the time-depth model/checkshot does not exist, set uncheck to this fill to set a constant velocity model to load the well. Later on the time-depth model/checkshot can be imported via the Well Manager. Additionally, specify whether the file is a checkshot data or not. The additional information (Well ID, Operator, State, Country) can be included in the well track by selecting the Advanced/Optional button.

Name the Output well and press Go, to complete the loading of well track. It will return a message, "Well track imported successfully". Press Ok to close information window. Press Dismiss to exit.

Note: The surface coordinates and elevation above surface are defined from the well track file. In normal cases, these definitions will be in the first line of the well track file. If the well track file starts below the datum (KB, Kelly Bushing), you will need to manually adjust these parameters in the well track file before importing it as a well track. Elevation above the surface is normally considered positive if the reference datum is above sea level. Conversely, if the elevation reference is below sea level, you can define the negative values in the elevation as those above the surface elevation reference.

Load Logs & Markers (via Well manager): Launch the Well manager

. Here you will find the loaded well track(s) from the previous step in the left panel.

To import Logs, select the recently loaded well and press theImport button. In pop-up window, select the input LAS log file, and then examine the file. The remainder of the window will be automatically filled in from input file. Importantly, if you only want to load certain logs, highlight only the wanted logs. (By default all available logs will automatically be highlighted.) Press Ok. The logs will be loaded and will appear in the right panel.

To import Markers, select the recently loaded well and press the Markers button. In pop-up window, select the Read file button and follow the same steps as before when loading Ascii files. Alternately, instead of reading a file, you can manually type in the depth, name and assign marker colors.

Updating well tracks, checkshot data, and depth to time models can also be done in this Well file management window.

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2D Viewer		Display loaded data