[OpendTect_Users] Sweetness Attribute

Mon Jan 27 14:12:16 CET 2014

Jack:

I do not know of an online resource, but basically the sweetness attribute
would combine all pitfalls found in amplitude and frequency analysis (note
that sounds worse than it is, if you know what you are doing, sweetness is
a really useful attribute).

Typical pitfalls are:
Amplitude term: being in a dim spot regime (sweetness will not work and you
are missing reservoir), false positives due to hard streaks (carbonates,
cemented sandstone, evaporates,..), high amplitudes due to volcanic derived
sediments, etc etc. Some you can screen for some of these problems, for
example hard streaks are supposed to have an opposite polarity. Hilterman's
DISC is probably excellent reading on this subject.

Frequency term: bad processing, gas chimneys (rather than gas filled
reservoir), reflections of rugose reflection surfaces (salt, erosional
surfaces), converted waves not accounted for. Again more found in
 literature.

So if you find an sweetness feature of interest, don't just assume it is
good, investigate further: know the regional stratigraphy, look at the
polarity, try to reproduce using forward modelling, create a HorizonCube
slice through the feature and investigate it's morphology, check its
downdip  limit (and consistency thereof) if you suspect sweetness to be
hydrocarbon related, etc etc. Note this can be done very easily in
OpendTect.

Hope this helps.

On Sat, Jan 25, 2014 at 12:20 AM, Jack Barajas <jack.barajas at gmail.com>wrote:

> Is there an online resource discussing the pitfalls if sweetness 1 and 2?
> --
> Jack
>
>
> On Sat, Jan 25, 2014 at 12:57 PM, friso.brouwer <friso.brouwer at dgbes.com>wrote:
>
>> 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
>>>
>>>
>>>
>>> _____________________________________________
>>>
>>>
>>>
>>> René Grobe, PhD.
>>>
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>>>
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