[OpendTect_Users] Time-depth horizon conversion

[Farrukh Qayyum]

Dear Emilson,

We normally do an on the fly time to depth conversion of the seismic 
data using a velocity cube. However, if you want to convert only time 
horizons into depth horizons within OpendTect then you will have to do 
the following steps.

   1. Go to Attribute set window (Main Menu > Analysis > Attribute > ...).
   2. In the pop-up attribute set window, you will have to find Horizon
      attribute in the list.
          * Select that attribute and provide an input seismic data on
            which the Horizon was being mapped.
          * Select the horizon that you want to convert into depth.
          * Do not change the default Output type. Please leave it 'Z'.
          * Provide an output name to this horizon attribute (e.g.
            Horizon A).
   3. The above step is done to get Z-values (in seconds) of a given
      horizon and then multiply the attribute with a velocity data. The
      next step is to do time to depth conversion:
          * Now find the Mathematics attribute in the list. In the
            formula bar, please type this: *HorZ * Vel/2*. Prese the
            /Set/ button. Here, we are using two variables. HorZ is the
            defined horizon attribute (Horizon A) and the Vel is a
            stored Velocity data. If you do not have any velocity data
            and you want to use a constant velocity, please replace the
            Vel variable to any constant value e.g. 3000.
          * Once you will press the /Set /button, it will ask you to
            provide the inputs for HorZ and Vel variables. Please select
            the right inputs as explained in the above bullet.
          * Give an output name (e.g. Horizon A depth) to this attribute.
          * Save the attribute set and press OK to the Attribute set window.
   4. Now create the grid output (Main Menu > Processing > Create Grid
      Output). In the pop-up window, please select the Quantity to
      output (here it should be the attribute i.e. Horizon A depth).
      Then also select the horizon for the /calculate on surface /field.
      Once done, press /Proceed/ button.

Please note that the horizon is saved as an attribute data (depth) on a 
selected horizon that can be exported as an ASCII grid. To export the 
attribute grid created in the step 4, you may use the export utility 
form the Main Menu > Export > Ascii .... In the /Export Horizon /window, 
select the horizon and the calculated attribute from the list and export 
it to a disk. This exported horizon can be used in the depth survey.

Best Regards,

Farrukh Qayyum
Geoscientist
dGB Earth Sciences B.V.
Nijverheidstraat 11-2,
7511 JM Enschede, The Netherlands.
Tel:	+31 53 4315155
Fax:	+31 53 4315104
http://www.dgbes.com
mailto: farrukh.qayyum at dgbes.com


On 06/30/2011 09:20 PM, Emilson wrote:
> Dear OpendTect users,
>
>
> Is there a way to convert time-horizons into depth-horizons within
> OpendTect?
>
>
> Thank you all,
>
> Emilson P. Leite
> DGRN/IG/UNICAMP
>
>
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> Users at opendtect.org
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>
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