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Introduction

The seismic interpretation tool lets you interpret horizons, faults and observations. This can be done both manually and automatically. In your Geocap project you will typically have an interpretation folder with one or more Ihorizon datasets, one Faults folder and one Observations folder.

The structure of a horizon in Geocap is as follows:

  • One horizon can contain interpretation from several seismic lines
  • Each line can have many segments
  • Each segment can have many picks

This means that each horizon will normally contain thousands of picks along different seismic lines. Each pick is stored with the following information:

  • Time value
  • Seismic line name
  • Shot point

The way Geocap stores its horizon data is compatible with most other seismic interpretation systems.

The seismic interpretation tutorial is found in the Shelf section Seismic Interpretation.

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In this section:

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Importing interpretation from external files

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The value of the amplitude spectrum at a specific frequency calculated by as Short Time Fourier Transform.

User-defined Function

Lets the user specify a mathematical function of the original seismic and the position of the sample in question.

For example you could use the function "abs(s)" to find the absolute value of the seismic.

From the Variables drop-down list you can choose from different variables such as I, inline trace position. Hoovering over a variable name brings up a description.

From the Functions drop-down list you can choose from many different mathematical functions such as abs(). Hoovering over a function name brings up a description.

Dip and Coherence

Right-clicking on a Seismic Line or a Seismic Brick Cube and selecting "Seismic Trace Attributes..." pops up the following dialog: 

Dip and Coherence dialog

 

The Coherence attribute is a byproduct of the dip telling us how reliable the InlDip and CrlDip estimates are: Dip and Coherence process estimate the surface normal G=[Gx,Gy,Gt] at each sample in the seismic from a statistical analysis of the samples in a window around the sample in question.

If there happen to be a minima or maxima at the sample; this surface normal will point in the same direction as the normal to the interpreted horizon going trough the sample. If not one can still imagine an implicit surface; where the seismic amplitude is constant.

From the surface normal: the following are calculated:

InlDip=Gx/Gt

CrlDip=Gy/Gt 

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The InlDip in a point (black circle) is the ratio of the inline, x, component of the surface normal to the t component of the surface normal, G (black vector) and therefore a measure of how much the implicit surface (green line) is dipping relative to the horizontal (blue line).  

 

Since the dip is calculated over a window the result is some form of average over the window and as a byproduct we therefore get Coherence which is a measure of how much the samples in the window are in accordance with this average, or how reliable the dip estimates are: 

0 <= Coherence <=1, where 1: absolute certain.

But it Coherence can also be viewed as a measure of "order" in the seismic. A non chaotic region of the seismic will have a high coherence, whereas a chaotic region, e.g. inside a salt, will have a low coherence. 

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A Seismic Line (left), its Dip (middle) and its Coherence (right).


Seismic Attribute Calculator

Right-clicking on a Seismic Line or a Seismic Brick Cube and selecting "Seismic Attribute Calculator..." pops up the following dialog: 

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The Seismic Attribute Calculator makes it possible to combine Seismic + up to 3 Seismic Attributes into a weighted combined Attribute. 

From the Variables drop-down list you can choose from different variables such as I, inline trace position. Hoovering over a variable name brings up a description.

From the Functions drop-down list you can choose from many different mathematical functions such as abs(). Hoovering over a function name brings up a description.