OpendTect dGB Plugins User Documentation version 4.2
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4.2. Interpretation Window

4.2.1. Overview

In OpendTect-SSIS, an interactive module is used to interpret a sequence in details. This is done by displaying the HorizonCube on an element (inline/crossline/2D line) and launching the interpretation setup:

Select the HorizonCube.
Add the HorizonCube display in the tree.
From the SSIS menu select SSIS > Interpretation > New/Edit or use the short-cut button from the SSIS toolbar.

Launch the interpretation window

This window is used for the sequence stratigraphic interpretation from the HorizonCube (2D/3D). The interpretation is done in an interactive manner i.e. by sliding the HorizonCube-slider up and down (right panel) and visualizing the depositional changes in the OpendTect scene(s). When a shift in depositional pattern is apparent, a sequence stratigraphic surface can be inserted by pressing the Insert button. This is also interactive, i.e. the slider will update the display in the OpendTect scene and the surfaces will be added in the graphical area (left panel) of the Interpretation window. An example of this interpretation window with a sequence stratigraphic interpretation is shown in the figure below.

Interpretation window for SSIS.

Open the stored interpretation. Note that more than one interpretation can be stored for any calculated HorizonCube.

Save the interpretation.

Save the interpretation with a new name i.e. Save As..

Select/Change the Sequence model.

Take a snapshot of the graphical area and save it.
Link to ColorTable: This options is used to lock the color table while moving the slider position up and down.

4.2.2. Select/Define a Depositional Model

Seismic sequence stratigraphic interpretations in SSIS are started by selecting/creating a depositonal model. The models are color-coded representations of system tracts in OpendTect and the corresonding base level curve is automatically drawn in the Interpretation system. To select/define such a model, click the Select Sequence Model

icon. By default, there are five different standard depositional sequence models available in the setup. Select any one of them or press Add Model to add a new model in the Systems tract setup window.

Default Sequence Models

The user defined Sequence Model
In order to define a new model, press the 'Add Model' button and type the name (Name for Model) in the pop-up window. Store the newly created model either for the current user or for the entire survey. On 'OK', a blank model will be added in the systems tracts Setup. Right-click on the Undefined text in the Name Column and select Insert row after sub menu. This will add a blank line below the undefined row. Type a name for the systems tract of the newly created model. To assign a color for the newly added systems tract, double click on the white cell of the same row. Select an appropriate color for the systems tract. Press OK to store the model.

4.2.3. Interpretation Workflow

After defining/selecting the right depositional model, you are ready to start interpreting sequence stratigraphic surfaces and the systems tracts. First, create an overlay of the HorizonCube on an inline/crossline/2D line, and position the scene in a way that you will notice main depositional changes (see below).

The displayed seismic data is on an inline and the displayed HorizonCube is created for the entire survey range. The interpretation window is placed to the left so that the identified sequence stratigraphic surfaces can be inserted easily.

Check the Link to ColorTable option to optimize (stretch/squeeze) the colors for the HorizonCube relative to the slider position. Now, move the Top slider slowly down/up to observe the depositional changes. Start your interpretation from the bottom events of the HorizonCube. Move the Top slider up from the lowest position and position it where you observe a depositional shift or a sequence stratigraphic surface. At this point, you can add a surface to the current interpretation. Press Insert button to add a sequence stratigraphic surface in the display panel. This will add an surface in the Systems Tracts (grey) column (as shown below).

The top slider position is adjusted to view at where the depositional chagnes are observed (e.g. in this case from transgression to normal regression).

Now, the next step is to assign a name to the sequence stratigraphic surface. Right-click within the gray area i.e. just below the newly inserted stratigraphic surface. In the pop-up tree, you will see four options. From the 'Assign Systems Tract' option, select a sequence systems tract. Once you have selected this, the package will be filled with the corresponding color. Note also, that the relative change in base level is automatically plotted according to the depositional sequence model. Now you can continue interpreting the entire section by positioning the slider to next position(s) and following the same steps.

The pop-up menu is briefly explained below:

Assign Systems Tract: Note that each depositional model has its own systems tracts-definition. Thus, if you have selected depositional model IV the corresponding systems tract that you can assign will be listed as above.
Edit Boundaries: If you are not satisfied with the inserted stratigraphic surface for the systems tract, select the 'edit boundaries' option from the tree. On the right panel you can move the HorizonCube-slider to a new position. When done, press Set button or Cancel edit.

Show Thickness Map

Set Absolute Age: Set the geological absolute age (My) to any stratigraphic boundary. In the next pop-up window, give absolute age for top and bottom of the system tract.

Save Interpretation

Once you complete your interpretation on the entire section, you are ready to save the interpretation. This can be done by pressing the save button

. By default, the interpretation is saved with a default name (Interpretation 1). Any HorizonCube can have more than one Interpretations. Therefore, you can also save the interpretation with another name by pressing the Save As button

Save Surfaces

A stratigraphic surface can be saved as an output surface. Either right click on the stratigraphic surface name, dots of base level curve or at numeric values of absolute age (if defined).

Once you are satisfied with the interpretation, press save or save as button to save the interpretation.

Select the area and write the name of output surface. This output surface can be displayed later from the Horizon tree.

You can also save all surfaces by pressing Save all surfaces button.

4.2.4. Display Systems Tracts

The interpreted system tracts in the interpretation window can be displayed on the inline/crossline/2D line using the pop-up menu accessed through right-clicking the elmenent on which the system tracts should be displayed. Select the Add Systems Tracts display option.

An example overlay of the interpreted system tracts (semi-transparent) on an inline from a 3D HorizonCube.

Change Transparency

To change the transparency of the system tracts overlay, right click on the systems tracts element from the tree (as shown below) and select the transparency-option from the pop-up menu. From the pop-up window (SystemTracts transparency), the transparency can be set by moving the slider towards the right or left.

Moreover, the Move option in the pop-up menu for the System Tracts changes the order of the system tracts within the element. However, it doesn't change the display layout in the OpendTect scene. Select Remove item to remove the display of the System Tracts from the scene.

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Sequence Stratigraphic Interpretation System (SSIS)		HorizonCube Slider