[Users] OpendTect workflow: blending attributes effective at different time or stratigraphic intervals

[Friso Brouwer]

I would like to share the following methods of blending 2 attributes 
within OpendTect Attribute Engine. One attribute that works well in the 
shallow part of a survey and one that works well in the deeper part of a 
survey. In addition, a modification is added, for blending 2 attributes 
that work above and below a certain horizon.

The situation that one wants to blend two attributes each effective in a 
specific level in the seismic data is a situation often encountered. For 
example due to different lithology's between stratigraphic levels, 
regional top of pressure and effects of burial (compaction, velocity 
increase) and increasing attenuation with travel time of the higher 
frequencies in the seismic wavelet.

For the following, go into the OpendTect Attribute Window

*Blending based on time:*

Assume you have a working ShallowAttribute  and DeepAttribute
 
Now create an attribute called TWT, using the Reference attribute with 
option Z in the OpendTect attribute engine.

Then use Mathematics attribute to create the blending between 
ShallowAttribute and DeepAttribute, by creating 3 attributes as follows:

FinalAttribute(actual output) :
(x0>1000)?x1:x2
x0: TWT
x1: IntermediateAttribute (below)
x2: ShallowAttribute

IntermediateAttribute
(x0<3000)?x1:x2
x0: TWT
x1: IntermediateAttribute2 (below)
x2: DeepAttribute

IntermediateAttribute2
((x0-1000)/2000)*x1 + ((3000-x0)/2000)*x2
x0: TWT
x1:  DeepAttribute
x2:  ShallowAttribute

By applying the final attribute, you will apply the DeepAttribute below 
3000ms, the ShallowAttribute above 1000ms and in between use a linear 
weighting depending on TWT.

*Blending using a horizon:*

A simple modification will allow you to use the same strategy using not 
a TWT but a stratigraphic horizon as boundary.

Assume you have a working ShallowAttribute  and DeepAttribute
 
Now create an attribute called TWT, using the Reference attribute with 
option Z in the OpendTect attribute engine.
 
Also create an attribute call TWTHorizon, using the Horizon attribute 
with the key horizon that serves as separation surface as input and 
output option the Z-value.

Then use Mathematics attribute to create the blending between 
ShallowAttribute and DeepAttribute, by creating 3 attributes as follows:

FinalAttribute (actual output):
(x0>x1-1000)?x2:x3
x0: TWT
x1:TWTHorizon
x2: IntermediateAttribute (below)
x3: ShallowAttribute

IntermediateAttribute
(x0<x1+1000)?x1:x2
x0: TWT
x1: TWTHorizon
x2: IntermediateAttribute2 (below)
x3: ShallowAttribute

IntermediateAttribute2
((x0-(x1-1000))/2000)*x2 + (((x1+1000)-x0)/2000)*x3
x0: TWT
x1: TWTHorizon
x2: DeepAttribute
x3: ShallowAttribute

By applying the FinalAttribute, you will apply the DeepAttribute below 
1000ms below the horizon, the ShallowAttribute above 1000ms above the 
horizon and inbetween use a linear weighting depending on TWT.

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