OpendTect User Documentation version 3.2
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Chapter 5. Menu - processing

Table of Contents
5.1 Attributes
5.2 Create Seismic output
5.3 Create output using Horizon...
5.4 Cross-plot
5.5 Re-Start
5.5 Madagascar
5.6 Generic Mapping Tools (GMT)
5.7 Batch Processing
5.8 PreStack gathers

5.1. Attributes

An attribute is a derived quantity from a seismic input set. Attributes in OpendTect are defined by a name, a value, and a position in 3D space (inline, cross-line, and Z (2WT or depth)). Attributes can be calculated from single-trace, multi-trace, and multi-volume inputs. They can be steered and/or chained. Steered attributes are multi-trace attributes in which the trace segments are found by following a (pre-)calculated dip-azimuth. Chained attributes are attributes derived from other attributes. For example, Similarity and Energy are separate attributes that can be chained to calculate the Similarity of the Energy using the "Position" attribute.

5.1.1. Attribute Set window

An attribute set is an entity consisting of a group of seismic attributes. Usually attributes in a defined attribute set have something in common. For example, all attributes in a set have the potential to highlight an object type of interest, or a combined attribute, using all other attributes as intermediate results, is the final desired output.

Attribute sets are created or modified by defining attributes with specific parameter settings. Some attributes will show Steering unavailable in the parameter settings field. The steering plugin created by dGB allows the user various advanced steering options.

OpendTect works with the concept of an "active" attribute set. At start-up, there is no active attribute set (unless you re-open a saved session). To select an existing set or to create a new one, select the corresponding option from the File menu. OpendTect is delivered with a default attribute set for some general testing (Fault, Chimney,Salt default attribute sets). This set can be selected from the Default set option under the File menu. To use a default set, you need to select the input seismic data and a steering cube (if steered attributes are available in the default set).

Clicking any attribute in the list will show the parameter settings of the attribute. Notice that OpendTect uses SI units. For details on each of the attributes see Appendix A. Note that some of the parameter options depend on whether you are using 2D or 3D data as input. For example, the inline and crossline stepout field will be replaced by a single trace stepout field. Generally, an attribute set can only contain 2D attributes or only 3D attributes. Mixed attribute sets are not possible.

When attribute parameters are updated, the modified attribute can be added to the attribute set with a new Attribute name by clicking Add as new. Clicking on any other attribute in the list means that the updated parameters are accepted, while keeping the original attribute name. The Revert button only reverts changes to the original state before clicking on another attribute in the set. When OK is pressed, the (updated) attribute set becomes the "active" attribute set. The attribute set is saved to disk when Save on OK is ticked. To save an attribute set under a different name, use the corresponding option under the File menu.

File - Auto Load Attribute Set ...
In previous versions, there was no "active" attribute set at start-up. There is a new way to have an attribute set already open at start up using the " Auto load Attribute Set " option in the File menu
This enables the user to choose the attribute set which will be active the next time he/she opens the survey.

File - Change input can be used to change the input data of all attributes in the "active" set simultaneously, which is useful in case, for example, a new seismic volume has become available.

5.1.2. Attribute Set toolbar

The attribute set toolbar contains icons to open, save, and apply attribute sets.

or File - New set clears the window to create a new attribute set. The attribute set name can be specified when you save the set (press OK, or select File - Save set menu option).
or File - Open set opens a previously saved set in the current project (from the directory Attribs/).
or File - Save set saves the "active" attribute set in the Attribs/ directory of the current project.
or File - Open default attribute set. This opens the Default attribute set. Filenames for input data must be re-specified.
or File - Import attribute set from another survey. This imports an attribute set from another project. Filenames for input data must be re-specified.
or File - Reconstruct set from job
Swift icon for direct display of the selected attributes with the current attribute parameters. the selected attribute is applied to the active display element (shown in reverse video in the tree). The main graphic interaction buttons and options remain active while the Attribute Set window is open, so you can change the active element.
File - Evaluate Attribute. Automatic variation and evaluation of attributes and attribute parameters. If you have an "active" attribute and the current display element is a slice (inline, crossline or time slice) or a horizon, a new window will pop up in which you can specify how to vary the parameters of the displayed attribute. For Example, Spectral Decomposition:

Here we create eight slices, with time gates of [-28,28] [-32,32] .... Use the slider to instantly move through all the slices. When an attribute has been evaluated on a surface, you have the possibility to save all created slices. Enable this by checking Store slices on Accept. The data will be stored as Surface data and can be reloaded via the tree.

Note:

Evaluate Attribute

Evaluate Attributes-flash tutorial

or File - Crossplot attributes. On pressing this button, you can choose attributes to crossplot. Multiple attributes can be selected. The attribute values are extracted at picked locations (see Section 2.2.2.5 on how to create a pickset). Once attribute values are calculated, the Crossplotting table pops up.

5.1.3. Input selection

Every attribute requires input data. Both stored data and already defined attributes can be used as input to a new attribute. In other words, attributes can be embedded. However, circular references are not possible.

5.1.3.1. Input selection for 2D attribute sets

Select from the stored data or from the list with already defined attributes in the current attribute set. When selecting from Stored data, the user can also choose which from the stored attributes in the selected Line Set should be taken.

5.1.3.2. Input selection for 3D attribute sets

Select from the stored data or from the list with defined attributes in the "active" attribute set.

5.1.4. Default attribute sets

OpendTect is provided with "Default attribute sets" to get the user started. By selecting a default attribute set, a window appears that asks the user to select the correct input volume(s) and the correct SteeringCube (see images below). These attributes (except "Evaluate Attributes") require the following dGB plugins:

SteeringCube: attributes and filters are calculated along user-driven, or data-driven directions
Neural Network analysis: both supervised and unsupervised neural networks allow generation of meta attribute volumes that highlight any object of interest (e.g: Chimney, Salt,...).

This new OD version comes out with new "default attribute-sets", which are added to the already existing attribute sets like NN ChimneyCube, NN SaltCube, Unsupervised Waveform Segmentation, dGB Evaluate Attribute, etc .

These new default attribute-sets are mainly filter attributes:

The Dip-steered median filter: This filter attribute was before known as "Median Dip Filter", it cleans up the seismic data, removing randomly distributed noise.

The Dip-steered Diffusion Filter: This filter is mainly used to sharpen faults.
The Fault Enhancement Filter: This type of filter is used in the Fault/Fracture analysis, it dramatically sharpens the faults, eliminates random noise. It is a combination of both the diffusion filter and dip-steered filtered.
The Seismic Filters Median-Diffusion-Fault-Enhancement: This is the same as the "Fault Enhancement Filter" but it enables to visualize and modify the parameters of the dip-steered median filter, dip-steered diffusion filter and Fault Enhancement Filter.
The Ridge Enhancement Attribute: This filter detects lateral lineaments using different steered similarities (in diagonal, parallel directions)

When using the default attribute sets, please keep in mind that some of the parameter options depend on whether you are using 2D or 3D data as input. For example, the inline/crossline stepout field will be replaced by a single trace stepout field in 2D. Note also that an attribute set can only contain 2D or 3D attributes. Mixed attribute sets are not possible.

In this new version, an extra help button is added in the attribute set window. The old button (lower help button in attributes set window) still directs the user towards the general "Attribute set window" help page while the new button (upper help button) will bring the user to the specific attribute help page in the attribute appendix list. (see images below for Similarity attribute as example)

5.1.5. Open an attribute set from...

Attributes are primarily stored in attribute set files of extension .attr. Nevertheless attribute definitions can also be found in the parameter files of a processing job when an attribute was used to process a volume or lineset.

It is possible to import the attribute set of an attribute file from the menu: File > Import set from file. Existing attributes are stored in the Attribs folder of each survey. Optionally, attributes from another survey may also be imported.

A second option is to re-create the attribute set of existing processing file in the menu: File > Reconstruct set from job file > Find from created cube.
Existing jobs are stored in the Proc folder of each survey, with the extension par.

All import new input volumes must be selected to replace the references stored in the input files.

5.1.6. Auto Load Attribute Set

By default, no attribute set is loaded at startup, but in this window, you can change this behavior to load a specific attribute set when starting OpendTect.

This window is available from the attribute set window in the menu File > Auto Load Attribute Set.

Please note that a similar function exists for sessions.

5.1.7. Calculate Attributes

Working in OpendTect environment is very flexible. The attribute evaluation process has been considered critically and thus several key options are available for the user. For instance, the Evaluate Attribute

is considered as intermediate (but not necessary) step to quickly analyze the different parameters of any attribute within the working environment (View tutorial-Evaluate attributes). Similarly, the user can create a list of seismic attribute definitions as a working set that later on can be updated. The attribute set is then used to calculate the seismic attributes along lines/surfaces. There are two possible ways of calculating seismic attributes in OpendTect: First, in order to calculate the results of any attribute in the foreground, user(s) can do it on-the-fly. Second possibility is to calculate attributes after evaluation by running a secondary process in the background. In OpendTect, seismic attributes are applied on several elements (inlines, crosslines, time slices, random lines, 2D lines, volumes, horizons etc).

The workflow to calculate the selected attribute is quite simple:

Define (or use existing) attribute Set and save. For details see earlier sections of this chapter.
Calculate on-the-fly or Create Seismic Output or Create horizon attribute output.
If attribute is not calculated on-the-fly, retrieve results by displaying attribute in tree.

The example of first step is given in following figure. It highlights the sequential process (notice gree arrows form left to right) of on-the-fly attribute calculation. Firstly, several attributes are defined. Secondly, by default, when a user presses OK button in Attribute Set window, the Save Attribute definition window will appear to save the attributes definition as an Attribute set. The attribute can then be applied on an inline (for instance) by adding a blank attribute (right-click on inline number). Right-click on the blank attribute and select the attribute (Select Attribute > Attributes > "User Attribute"). The listed attributes are those that are defined in the attributes set window. Selection of any one, would start a process of on-the-fly attribute calculation. By following same workflow (as elaborated in figure) the same attribute can be calculated along other elements (e.g. crosslines, time-slices, volumes etc).

Schematic flow of on-the-fly seismic attributes evaluation on an inline.

Note: There are some attributes that can take to much time during the on-the-fly calculation process. This depends upon the type of attribute that how much calculation steps it considers e.g. multi-trace (e.g. coherency) attributes normally take more calculation times than the single trace (instantaneous) attributes. Similarly, the attributes with steering normally takes more time in calculation. So, each time the attribute is displayed in the scene (as shown above), it is calculated in the fore-ground. If the user is committed with the attributes results, this can be resolved by creating seismic outputs (See Section 5.2 and Section 5.3) in the background. This will also help to restore the saved sessions quickly.

Another example of second step, is shown in following figures. The attribute can be calculated along horizon by following the same steps described above, for inserting and displaying the attribute (as shown below). In this example, Coherency is calculated on-the-fly along a horizon. This attribute normally takes time (depending upon amount of traces involved). So, user can take benefit of saving the on-the-fly results that later on can be retrieved.

Schematic flow of on-the-fly seismic attributes evaluation at a horizon.

In order to save the calculated attribute as surface data, right click on the attribute and select Save Attribute. In pop-up window edit the name accordingly and press OK. This will save the horizon attribute as its surface data. That can be managed later on by using horizon management window. (see Chapter 4.5.3)

Result of calculated coherency attribute. Saving the horizon attribute as surface data

The stored attributes along horizon can be retrieved as surface data. Right-click on horizon and add blank attribute. Right-click on the newly inserted blank attribute and locate Surface data item in the sub-list of attribute (as shown below). In the surface data selection window, select the desired attribute. This will display the selected attribute in the scene.

Retrieving the stored surface data (attribute) of a horizon.

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