[Users] How-to: extract a 3D enveloppe of a chimney ?

[Aurélien]

Dear OD users,

I did a Chimney cube using the standard procedure. So, it means that I 
have a very nice chimney :-)
But now, I would like to represent it in 3D as it looks like a very nice 
plume through sediments (see picture attached)

There is several issues to do this:
1) propagate something between the chimney and the non-chimney (user 
controlled) to get the enveloppe in 3D.
2) remove all the data and/or values with a "chimney amplitude" lower 
than x (x= limit between chimney and non-chimney) and display the result.
3) I don't know yet ;-)

I didn't find any tool able to perform it in OD.

Does anyboby knows how to ?

Hope I am clear.

Cheers,

Aurelien Gay
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Geology and Geophysics Research Group
National Oceanography Centre
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Arnaud Huck a écrit :
> Dear OpendTect user,
> A common way at using inverted volumes is to extract thickness maps. 
> From an inverted impedance volume, and based on well analyses to 
> define cut-offs, it is possible to separate sands from the background 
> impedance data.
>
> Let's assume such an analysis would have told us that (absolute) 
> impedances lower than 9.000 (m/s)x(g/cc) are related to sands. In 
> OpendTect, you can derive from such a cut-off thickness maps in less 
> than five minutes with the help of three combined attributes:
>
> 1) At first, you need to enter you cut-off in a attribute of type 
> "Mathematics". The formula would be the following (if-then-else 
> statement):
> x0 < 9000 ? 1 : 1e30
> where x0 is your impedance volume.
> This attribute is acting like a flag, giving us the sample locations 
> where impedance is lower than our threshold, while the other samples 
> are set to 1e30, which is our undefined value.
> We can call this attribute "Blank outside".
>
> 2) Secondly, the thickness map itself is drawn by summing the number 
> of samples set to 1 in our region of interest. This region is 
> delimited by a time-gate, relative to the horizon on which we will 
> apply this attribute.
> For this purpose, we use an attribute of type "Volume statistics". The 
> input data is the previous attribute "Blank outside", you can enter 
> your desired time-gate. The stepout is 0 / 0 (trace-by-trace process), 
> Output statistic is "Sum", and Steering is set to "None" as we will 
> apply it on an horizon. Undefined values are not contributing to the sum.
> We can call this attribute "Sum thickness", and returns a number of 
> (flagged) samples
>
> 3) The third attribute aims at converting the result of the second 
> attribute in meters or seconds.
> If your impedance volume is in depth, you just need to multiply the 
> previous attribute by the depth sampling rate.
> In a more normal situation, your impedance cube is in time, and then 
> we need to multiply the "Sum thickness" attribute by the (time) 
> sampling rate, 4 msec. for instance, and by the average interval 
> velocity within your formation. This is done with a second 
> "Mathematics" attribute, with the kind of formula:
> x0*0.004*2000.0
> where x0 is the "Sum thickness attribute", 0.004 is the sampling rate 
> in seconds, and 2000.0 is the interval velocity in m/s.
> The thickness returned would then be in meter. We can call this 
> attribute "Thickness in m." for instance.
> Optionnaly, you can also read the velocity from another volume if 
> available.
>
> Finally, you can get your thickness map by applying the "Thickness in 
> m." attribute allong your horizon. Please note that you can also use 
> this approach with lithologies/facies cubes.
>
> If you have any questions, do not hesitate to ask me.
>
> Best regards,
> Arnaud Huck
> Geoscientist.
>
> -- dGB Earth Sciences B.V.
> -- Nijverheidstraat 11-2, 7511 JM Enschede, The Netherlands
> -- mailto: arnaud.huck at dgb-group.com, http://www.dgb-group.com
> -- Tel: +31 53 4315155 , Fax: +31 53 4315104
>
>
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>
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