[OpendTect_Users] Prestack Avo attributes.

[Paul de Groot]

Hi Mike,

1. is there a way to tell which Zoeppritz approximation it uses, and/or to
chose which version to use?

In OpendTect the full Zoeppritz equation is solved when we create
synthetics in the SynthRock plugin. Zoeppritz is not used in the pre-stack
tool where the input is real data. When you are dealing with angle stacks
than the pre-stack tool directly operates on the amplitude values of the
gather. If the input gathers are offset gathers and the requested output is
an AvO attribute OpendTect transforms the offsets to angles. This is done
through ray-tracing in a horizontally flat earth. The ray-tracer outputs
incidence angles. For this you do not need Zoeppritz. There is one
important issue to be aware of: OpendTect comes with a simple ray-tracer
that only approximates the angle of incidence. If you have a license for
SynthRock you can use its sophisticated ray-tracer to compute the angles of
incidence more accurately which will result in more accurate AVO attributes.

2. Can you calculate multiple attributes at once? e.g. Intercept and
gradient at the same time.

The attribute engine is designed such that it knows which attributes are
derived from the same pre-processed results, which saves CPU time. For
example, if you want to output all components of a spectral decomposition
you do the following: 1) you add the spectral component attribute to your
attribute set, e.g. sd 5Hz (with a step of 5). 2) you go to the Processing
menu to create a seismic output volume. 3) in the "Create Output Attribute"
window you select the sd5 attribute and you press Proceed. 4) A window as
attached pops up in which you specify all components that you wish to
compute. These components will be stored in a multi-component data set. (A
hidden feature in v4.6: to movie-style examine the components you select
all components and display these into one single display element. You then
step through the components one-by-one using the Page Up and Page Down
buttons. We will demo this in the Master Class that will be held before the
EAGE conference on June 15th in Amsterdam. There are still a few seats
available. If you want to join us please contact marieke.degroot at dgbes.com
.)

Unfortunately, this type of CPU optimization is not implemented for all
attributes. For Pre-stack attributes you will have to compute Intercept and
Gradient in separate runs. *Support *is cc-ed on this email to investigate
whether Pre-stack attribute computation can be optimized in a similar way
and if so to add this to the wish list.

Best regards,

Paul.


-- 
*Paul de Groot**President**______________________________*

*dGB Earth Sciences*Phone:+31 53 4315155E-mail:paul.degroot at dgbes.com
Internet:dgbes.com & opendtect.org*______________________________*


On Thu, May 29, 2014 at 7:35 AM, Mike Stone <mstone at act3solutions.com>
wrote:

> Couple dumb questions about the Prestack tool in the attribute calculator.
>
> I was looking at it earlier today, and I had two questions...
>
> 1. is there a way to tell which zoeppritz approximation it uses, and/or to
> chose which version to use?
>
> 2. Can you calculate multiple attributes at once? e.g. Intercept and
> gradient at the same time.
>
>
> Thanks,
>
>
>
> Mike Stone
> 832-768-0884
> MStone at ACT3Solutions.com
> Mike.Stone at Lukoil-Overseas.com
>
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