Attribute analysis is one of the key functionalities in OpendTect. Attributes are used for two purposes:
Visualization: you create a new view of the data that may lead to new geologic insight.
Integration of information: combine attributes, e.g. using neural networks (neural networks plugin needed).
To use attributes, you must define an attribute set (Processing menu - Attributes, or press the Attributes icon). To start: either create your own attribute set, or select one of the default sets. It is possible to calculate attributes from attributes and to use mathematics and logics (if .. then .. else ..) to create your own attributes. The sky is the limit! The attributes defined in this window are the recipees for making the calculations. You can either use these recipees to create new attribute volumes (Processing menu - Create seismic output), or for quick on-the-fly calculations (right mouse click on the element in the tree). The system only calculates what is needed for creating a display. For an optimal use of the system you are advised to limit on-the-fly calculation of attributes and evaluation of parameter settings to small areas (part of an) inline, crossline, time-slice, 3D sub-volume, random line, or 2D line). Inline calculations are in general the fastest. Processing of large volumes needs time and is best done in batch mode so you can retrieve from stored data afterward.
Attributes are an integral part of OpendTect. If you also have Dip-Steering plugin you can improve multi-trace attributes by extracting the information along a virtual horizon. This is called dip-steering and is supported for 2D and 3D seismic. In addition you will have a number of extra attributes: dip, azimuth, curvatures.
Purpose: Find the best parameter setting for a particular attribute. Theory: Use visual inspection, common sense, experience, and seismic knowledge to evaluate attributes that are appropriate for what you are studying. Software: OpendTect
Workflow:
Add an element to the tree, resize and position it to where you want to do the evaluation.
Open the Attribute Set window.
Add an Attribute to the list (e.g. Energy).
Press the Evaluate Attribute icon.
Specify the parameter to evaluate (Energy only has one: Timegate).
Specify initial value, increment and number of slices (e.g. [0,0],[-4,4] and 10, results in 10 energy calculations with time-gates: [0,0], [-4,4], [-8,8] ...[-36,36]).
Press Calculate. Note that the calculation will be done on the active element in the tree!
Use the slider to movie-style inspect the results and select the one you like best.
Tips:
To reduce calculation times reduce the size of the element. Inlines are generally faster than cross-lines, which are faster than time-slices.
When you add the element in the tree Add a second attribute to the element. Put the seismic in the first container and use the second container for the attribute evaluation. You can now switch element 2 (the top one) on/off to compare the attribute response with the seismic display.
