Friday, 8 May 2015

AVO Screening (Part 2): AVO colour blends

GeoTeric's colour blending and volume comparison capabilities can be used very effectively to screen for AVO anomalies and get an initial understanding of areas where you want to focus on for a more detailed AVO analysis.

Three angle stacks are required as the input for the workflow. Noise Cancellation can be applied to them, as long as the same filter and footprint size is used for all the three stacks. However, the use of Spectral Enhancement is not advised as amplitude preservation is critical for the accuracy of the AVO work.

The aim of this workflow is to produce a RGB colour blend combining the envelopes of different stacks. Like with the frequency decomposition RGB blends, this provides a very intuitive and stark representation of geological elements in the subsurface. Colour differences will represent changes in the relative amplitudes of the angle stacks, which could represent AVO anomalies.

The procedure to create the angle stack blend is:
  • Load the three angle stacks into GeoTeric. The amplitude relationships have to be preserved so if loading a floating point dataset, it is advised to use User scale when loading the volumes, so that the same scale factor can be applied to all the three stacks.
  • Produce the envelope volumes for each of the angle stacks. You will find the envelope attribute in Processes & Workflows -> Processes -> Trace Attributes -> Attributes.
  • Create a new RGB blend by highlighting the colour blends folder in your project tree and clicking “New Colour Blend” under proprieties.
  • Select the three angle stacks for your three colour channels (red – green – blue). Make sure you select Uniform in your scale options, so that the relative amplitudes of the three stacks are maintained.

The image shows a time-slice through a Near-Mid-Far envelope blend in the Parihaka dataset
(Taranaki basin, New Zealand), showing a feature with a very high amplitude in the far stack.

Coming soon... part 3, where we will cover how to generate gradient and intercept volumes.

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