[OpendTect_Users] Sweetness Attribute

[friso.brouwer]

Rene,

The sweetness attribute is a plain and simple tool to highlight 1) thick
clean reservoir, and/or 2) hydrocarbons (HC) filled reservoir.

Principle is you divide a amplitude attribute with a frequency attribute.

For reservoir (low AI sand embedded in shale) the effects are that when the
reservoir gets cleaner or thicker, the amplitude term increases due to
higher reflectivity and frequency of the combined reflections lower as the
thicknesses increases.

For HC presence (assuming an AVO 3 environment, where introduction of HC
leads to brightening), the effects are when HC gets introduced that
amplitude increases due to higher reflectivity and frequency of the
reflection is lower due to the combined effects of HC on the frequency
content.

>From the mathematical formulation you see that all these effects work in
the same direction. Of course it is also a very simple attribute and there
are lots of pit-falls, which I will not list here, as it is a bit besides
your question.

The inst. amp / sqrt(inst. freq) is the original definition of this
attribute, but it is easy to understand you can stick different terms in
the equation for the amplitude related numerator and frequency related
denominator and stay true to the underlying concept. The results will be
strongly related, but not equal. I often use the instantaneous amplitude in
the numerator as it removes the question what the best time gate, but I do
not like to use the instantaneous frequency as it is sensitive to thin beds
(which is, by the way, the basis of Tury Tanner's thin bed attribute).
Putting a square root operator in the denominator compresses its original
dynamic range and limits the effect of the higher frequencies.

The nice thing of the attribute is that you can do other things as well,
which are all quite easily implemented using OpendTect's mathematics
attribute and other attributes:
* Using energy instead of rms or inst. ampl in the numerator, which expands
the dynamic range of the amplitudes and focuses the results on the very
high amplitudes only.
* Replace the amplitude term with a far stack amplitude or an AVO attribute.
* Shift the frequency range, such that, with the original range going from
Fmin to Fmax, the shifted range goes from c to Fmax-Fmin+c (with 0< c <<
Fmin), this will really boost the effect of low frequencies in the
sweetness attribute response.
* Shift the time gate of the frequency attribute, such that the frequencies
are extracted below the evaluation point. This is very useful as most
frequency effects due to HC are found below the reservoir reflection.

So it is a really nice attribute to play with and optimize doing
recognizance type evaluation of reservoir and HC presence, but be cautious
in its interpretation, as there is a long list if pitfalls.

I hope this helps you forward.



>
> ---------- Forwarded message ----------
> From: René Grobe <grobe at geo-t.de>
> Date: Fri, Jan 24, 2014 at 2:17 PM
> Subject: [OpendTect_Users] Sweetness Attribute
> To: users at opendtect.org
>
>
> Hi All,
>
>
>
> as non-geophysicist I have a question about the definition of the
> “Sweetness” attribute. In literature the sweetness attribute seems to be
> usually mathematically defined as “Sweetness(1) = Instantaneous
> Amplitude/Sqrt(Instantaneous Frequency)”. In the OpendTect Attributes
> Matrix (https://opendtect.org/opendtect_attributes_matrix/) “Sweetness(2)
> = RMS Energy/Average Frequency” or “RMS Amplitude/Average Frequency”. It is
> clear that both definitions - Sweetness(1) and Sweetness(2) - generally
> relate Amplitude to Frequency, but do they exactly produce the same result
> or do they differ in any way? If so, how can one describe the difference
> and its impact on interpreting the result?
>
>
>
> Thank you very much!
>
> Best regards,
>
> René
>
>
>
> _____________________________________________
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