Combined Attribute Displays

transcript

Combined Attribute DisplaysCombined Attribute Displays

Seismic Attributes

“from a different point of view”

Steven Lynch

Divestco Inc

CREWES

s Overview

• Review the theory behind Instantaneous Seismic Attributes.

• Introduce the Combined Attribute Display.

• Present a series of examples of various attribute combinations.

• Conclusions.

s Instantaneous Seismic Attributes

“The conventional seismic trace can be viewed as the real component of a complex trace…. The complex trace permits the unique separation of envelope amplitude and phase information and the calculation of instantaneous frequency”. (Taner, et al, 1977)

( ) ( )cos ( )

*( ) ( )s

Quadrature

in ( )

) *( ) ( ) j t

f t A t t

F t f t jf t A t e

A(t) is called the Amplitude or Reflection Strength.

(t) is called the Instantaneous Phase.

The Instantaneous Frequency is the rate of change of the Instantaneous Phase.

The Weighted Average Frequency is the I.F. weighted by the Instantaneous Power (A(t)2) and averaged over an 11 point Hamming window.

( )( )

d tw t

( )( ) ( ) j tF t A t e

s Seismic Data

3D (SeisScape) display of the seismic data.

s Reflection Strength

Phase independent amplitude that may have its maximums at places other than peaks or troughs

s Instantaneous Phase – V.D.

Amplitude independent phase which emphasizes the continuity of events

s Instantaneous Frequency

A sample by sample estimate of a trace’s dominant frequency.

s Weighted Average Frequency

Fourier spectral average over a window.

Instantaneous Attributes are widely used in exploration, especially in stratigraphic analysis and in analyzing the presence of gas.

However, they are several problems with them.

1. When looking at an attribute display we loose the seismic itself.

2. Instantaneous Phase and Frequency, being amplitude independent, are susceptible to noise spikes at low amplitudes.

What we would like is a display that quickly relates the attribute back to the seismic it was created from and that can help us filter out spurious noise.

We want to make them more interpretable!

s Combined Attribute Display

Combined Attribute Display is a technique for viewing up to three attributes on the same display.

They have three independent components.

1. 3D representation of a seismic attribute.

2. Coloring of the 3D display.

3. A “Sea Level” variable density plane.

s Variable Density Display

Variable density display of a small channel.

3D Attribute Display, in this case the attribute is the seismic data itself.

3D Attribute Display coloured using a separate attribute.

The “Sea Level”, a Variable Density slice.

The final display with all three components.

s Combined Attributes

3D Surface Colour Attribute Sea Level

Reflection Strength Seismic Amplitude None

Seismic Amplitude Reflection Strength None

Seismic Amplitude Instantaneous Phase None

Instantaneous Freq. Weighted Freq Seismic Amplitude

Weighted Freq Seismic Amplitude None

3D Attribute Display coloured using a separate attribute.

s Reflection Strength

3D Display of the Reflection Strength.

s Reflection Strength/Seismic Amp.

3D Reflection Strength coloured by the seismic amplitudes.

s Reflection Strength/Seismic Amp.

Notice how the polarity “twists” across the R.S. peak.

3D display of the seismic data.

s Seismic Amplitude / Reflection Strength

3D seismic data coloured by the Reflection Strength.

s Seismic Amplitude / Reflection Strength

Notice again how the high energy twists off the peak.

s Instantaneous Phase

“Sea Level” display of the Instantaneous Phase.

3D display of the seismic data.

s Seismic Amplitude/Instantaneous Phase

3D seismic amplitudes coloured by the Instantaneous Phase.

s Instantaneous Frequency

3D display of the Instantaneous Frequency.

Sea Level

s Inst. Freq./Wt. Freq./Seismic Amp.

3D Instantaneous Frequency coloured by the seismic amplitudes.

s Weighted Average Frequency

3D display of the Weighted Average Frequency

s Weighted. Freq./Seismic Amp.

3D Weighted Average Frequency coloured by the seismic amplitudes.

s Conclusions

3D Attribute Displays are:

– Dramatically more informative than typical variable density displays.

– A lot more fun to work with.

Combined Attribute Displays are:

– A way of looking at multiple seismic attributes on the same display.

– Potentially more intuitive.

– Easier to relate observed anomalies back to the seismic that they were created from.

Combined Attribute Displays

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