OpendTect User Documentation version 4.2
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Chapter 6. Menu - Analysis

Table of Contents

6.1. Attributes
6.2. Volume Builder Setup
6.3. Cross-plot
6.4. Tie Well to Seismic

The Analysis menu contains the following sub-menus (see figure below). The description on each sub menu is described individually in different sections of this chapter. Whereas, the Neural Network analysis is a dGB-plugin, which is separately described in dGB-plugin documentation.

6.1. Attributes

In OpendTect, seismic attributes are calculated/evaluated by using Attribute-set Window. In this window, many single/multi trace, pre/post-stack, dip-steered/non dip-steered attributes are available. Moreover, it also contains special filters (e.g. Gap decon, Frequency filters, dGB-special filters etc). The attributes are explained separately in the Appendix-A.

6.1.1. Attribute Set window

An attribute set window contains a set of seismic attributes definitions that are to be evaluated/calculated. The window functions dual purposes while defining the attributes i.e. a user can work in the active scene while creating an attribute definition and a user can also calculate attribute after saving the attribute set. In broad sense following work flows are applicable in OpendTect attribute calculation process (on sections and horizons):

Evaluate attribute
On-the-fly attribute calculation
Creating an attribute output (2D/3D)

In following figure, three different attributes are defined as an attribute set in the list, which is considered as a routine practice in OpendTect environment (especially to define a meta-attribute). These attributes can be; evaluated on sections and horizons, applied on-the-fly and created as an output attribute. Importantly, some attributes will show steering selection in the input parameter settings. The dip-steering plug in created by dGB provides various advanced steered attributes for the users.

OpendTect works with the concept of an "active" attribute set. At start-up, there is no active attribute set. To create a new one (New set ...), or to select an existing set(Open set ...) , select the corresponding option from the File menu (See below). OpendTect is also 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 an 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 changes 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.

6.1.2. 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

By pressing this button, a user can choose attributes to crossplot. Multiple attributes can be selected. The attribute values are extracted at picked locations (see how to create a pickset). Once attribute values are calculated, the crossplotting table pops up.
Moves an attribute Up/Down for rearrangement.
Sort attributes alphabetically.

6.1.3. Auto Load Attribute Set

By default, no attribute set is loaded at startup. These settings can be over-ruled by selecting a specific attribute set to be auto-loaded in the list each time a user restarts the OpendTect window. This can be set from the attribute set window under File > Auto Load Attribute Set sub-menu. If selected, it will launch the auto-load attribute set window. Selecting Yes will show the list of attribute set to be auto-loaded. Select one attribute set and press Ok button. This will save the settings and next time, whenever the OpendTect is started, the selected attribute set will be auto loaded. Such practice becomes useful when a user works with attributes evaluation at different stages of a project and he/she has to update the same attribute sets. In this way, the same definition is launched thus a user does not need to open the attribute definition again and again.

Load Now will directly load the selected attribute set, if not selected the attribute set will be loaded the next time the user opens the survey.

Please note that a similar function exists for sessions.

6.1.4. 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 steering cube (see images below). These attributes (except "Evaluate Attributes") require the following dGB plug-ins:

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, Faults, Salt,...).

The OpendTect 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 .

Evaluate Attributes: This default attribute set contains the default definitions of several basic attribute that are grouped together to give an idea of attributes evaluation in OpendTect. Beginners can select this default attribute set to start with the OpendTect. After selection, only input seismic data is required.
dGB Evaluate Attributes This default attribute set is also similar to above attribute set with additional dGB attributes (using dGB plug-ins). For this set, both seismic and steering data are required as input.
The Dip-steered median filter: This default attribute set contains the definition of dip-steered median filter. It cleans up the seismic data by removing random noise. Both seismic and steering data are required as input.
The Dip-steered Diffusion Filter: This filter is mainly used to sharpen faults. Both seismic and steering data are required as input.
The Fault Enhancement Filter: This type of filter is used in the Fault/Fracture analysis, it dramatically sharpens the faults by supressing random noise. It is a combination of the diffusion filter and the dip-steered filtered. Both seismic and steering data are required as inputs.
The Ridge Enhancement Attribute: This filter detects lateral lineaments using different steered similarities (in diagonal, parallel directions)
NN Fault Cube: A dGB standard default attribute set containing the definitions of all attributes that are used in neural network (NN) training to create meta-attribute i.e. NN Fault Cube.
NN Chimney Cube: A dGB standard default attribute set containing the definitions of all attributes that are used in neural network (NN) training to create ChimneyCube (meta-attribute).
NN Salt Cube: A dGB standard SaltCube meta-attribute.
NN Slump:A dGB standard SlumpCube meta-attribute.
Unsupervised Waveform Segmentation: It is an attribute set containing the definition of attributes that are used in unsupervised waveform segmentation (a.k.a UVQs).
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.
Fault Enhancement Attributes: An expandable attribute set containing the list of the attributes that are useful for fault visualization and fault interpretation.
NN Fault Cube Advanced: A most superior FaultCube (meta-attribute) attribute set that is used as input for neural network training to create fault probability cube.

A default attribute sets window containing the list of all available default attributes

When one of these default attribute-sets has been selected, a window pop-ups that allows the users to select the input seismic and optionally a steering if this is required.(see image below)

Inputs selection window

6.1.5. 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.

6.1.5.1. Input selection for 3D attribute sets

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

In case the input data is multi-component, the user will have an option to choose amongst all available components as shown below.

Note: The Filter section allows the user to quickly find the right input. e.g type *S will look for all attributes/cubes started with S like Similarity.

6.1.5.2. 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. If the selected cube is multi-component, the user will get an option to choose which component to select as input data.

6.1.6. Import 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 line set.

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. There are two options available to reconstruct the attributes definition: from an existing par-file or from a created cube file. In first case (from par-file) select the input parameter (*.par) file. In second case (find from created cube), another window pops-up in which the input volume and the corresponding parameter file are selected. The file name is found automatically.

Finds the attribute set from an existing (created) cube, which was calculated inside the OpendTect.

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

6.1.7. Calculate Attributes

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:
1. 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 Create Volume Output and Create Grid Output sections) in the background. This will also help to restore the saved sessions quickly.

2. Additionally, multi-component output seismics-2D/3D (like spectral decomposition) are created by using create volume output.

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, Similarity 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 Horizon file management window)

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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