New user, how to do time-depth conversion for a single 2D line

[Md Ariful Islam]

Hi,

I only have two 2D seismic lines and average velocity values for water column, sedimentary layers and crystalline basement. Now I need to convert the image into depth domain. I am very new in this, I tried opendtect youtube tutorials but I couldn't find one. I tried creating velocity models but I failed. Please help me with your expertise.

I'm linking one of the lines because these files are kind of different than other files I tried to open. I can't open them in the main window, it opens only in 2D viewer option.

https://uofnelincoln-my.sharepoint.com/:u:/g/personal/ifilina2_unl_edu/EewQjxN1KjZJg1BtwNwJ3o8ByksBPnrCn-O2pMz4fq2zIw?email=users%40opendtect.org&e=KCLoGg

[satyesh bhandari]

Hi,

Without the velocity information of sedimentary layer it is not possible to convert a time section into a depth section.

However, to get a simple depth section there is way around. Prepare a layered velocity model. Just correlate water bottom reflector and any two other strong reflectors. Even a water bottom reflector is sufficient if you don’t have other. Apply a velocity of 1500 m/s for water layer and about 2000 m/s for sedimentary layer. The depth error will be in the range of +/- 1-2 percent for shallow targets and about 5 percent for deeper targets for more than 2000 mts.

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[Md Ariful Islam]

Hello, 

Thank you very much sir for your reply. I'm very new with seismic data that's why probably having a hard time doing this. 

I am assuming 3 velocity values for three layers ( water - 15km/s, sedimentary layer 2.2km/s and crust 6.5km/s). 

But I don't know how to create a velocity model from that for Time-Depth conversion.

Could you or anyone else please give me a little hint how to so this in OpendTect. 

Thank you very much. 

[MICK]

Do you have horizons picked for the various boundaries sea floor, base sediment , base crust?

If so depth is :

 

seafloor TWT/2*1.5 +( base sed TWT- Seafloor TWT)/2*2.2 + (twt – Base sed tWT)*6.5

 

You don’t need opendtect for this – you can do it in excel.

To view this discussion on the web visit https://groups.google.com/a/opendtect.org/d/msgid/users/e9cdb2cf-b32e-49e9-81c1-2eb0c11c3185n%40opendtect.org.

[lviertel]

Hi,

Maybe this is useful to you.

I would do it in a quick way as follows:

Create your velocity model using 3 colors in any paint package you like. Make sure you keep scale and proportions. You can take an image of the line and paint on top.

Load your image into matlab.

convert image to segy using matlab script "image2segy". You need to know the navigation or extract from the original segy.

if you know well matlab change value of color A by velocity of layer 1,  value of color B by velocity of layer 2,  value if color C by velocity of layer 3 and export the segy (you will need to tweak the script a bit)

or

export the segy and load load into matlab again using any seismic package like seislab, and then replace from segy value of color A by velocity of layer 1,  value of color B by velocity of layer 2,  value if color C by velocity of layer 3. You need to work with 16 or 32 bit floats as 6500 m/sec is larger than 256 (8 bit)

export again and load into opendtect as a segy velocity line


Hope this helps.

Once done once is more easy than it looks.

Cheers,

Luis

At 09:26 PM 10/11/2021, Md Ariful Islam wrote:

Hello,
Thank you very much sir for your reply. I'm very new with seismic data that's why probably having a hard time doing this.
I am assuming 3 velocity values for three layers ( water - 15km/s, sedimentary layer 2.2km/s and crust 6.5km/s).
But I don't know how to create a velocity model from that for Time-Depth conversion.
Could you or anyone else please give me a little hint how to so this in OpendTect.

Thank you very much.



On Sunday, October 3, 2021 at 4:58:22 AM UTC-5 satyesh.bhandari wrote:

Hi,

Without the velocity information of sedimentary layer it is not possible to convert a time section into a depth section.

However, to get a simple depth section there is way around. Prepare a layered velocity model. Just correlate water bottom reflector and any two other strong reflectors. Even a water bottom reflector is sufficient if you don’t have other. Apply a velocity of 1500 m/s for water layer and about 2000 m/s for sedimentary layer. The depth error will be in the range of +/- 1-2 percent for shallow targets and about 5 percent for deeper targets for more than 2000 mts.

Â

From: Md Ariful Islam <arif94...@gmail.com>

Sent: 02 October 2021 23:53

To: OpendTect Users <us...@opendtect.org>

Subject: [OpendTect_Users] New user, how to do time-depth conversion for a single 2D line

Â

Hi,

I only have two 2D seismic lines and average velocity values for water column, sedimentary layers and crystalline basement. Now I need to convert the image into depth domain. I am very new in this, I tried opendtect youtube tutorials but I couldn't find one. I tried creating velocity models but I failed. Please help me with your expertise.

I'm linking one of the lines because these files are kind of different than other files I tried to open. I can't open them in the main window, it opens only in 2D viewer option.

Â

https://uofnelincoln-my.sharepoint.com/:u:/g/personal/ifilina2_unl_edu/EewQjxN1KjZJg1BtwNwJ3o8ByksBPnrCn-O2pMz4fq2zIw?email=users%40opendtect.org&e=KCLoGg

Â

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[MICK]

Don’t forget the /2 at the end of the formula

 

From: MICK [mailto:mic...@bigpond.com]
Sent: Tuesday, 12 October 2021 3:48 PM
To: us...@opendtect.org
Subject: RE: [OpendTect_Users] New user, how to do time-depth conversion for a single 2D line

 

Do you have horizons picked for the various boundaries sea floor, base sediment , base crust?

If so depth is :

 

seafloor TWT/2*1.5 +( base sed TWT- Seafloor TWT)/2*2.2 + (twt – Base sed tWT)*6.5/2

To view this discussion on the web visit https://groups.google.com/a/opendtect.org/d/msgid/users/000c01d7bf3d%2483093d10%24891bb730%24%40bigpond.com.

[MICK]

Further to my previous  reply try

Analysis-> velocity model building à horizon based velocity model (or similar – I cant recall the exact headings)

 

 

 

From: Md Ariful Islam [mailto:arif94...@gmail.com]

Sent: Tuesday, 12 October 2021 1:26 AM
To: OpendTect Users <us...@opendtect.org>
Cc: satyesh.bhandari <satyesh....@gmail.com>

To view this discussion on the web visit https://groups.google.com/a/opendtect.org/d/msgid/users/e9cdb2cf-b32e-49e9-81c1-2eb0c11c3185n%40opendtect.org.

[Mark Crawford]

Hi,

To actually create a Simple Time-Depth Model, go to:

Processing > Create Seismic Output > Velocity > Time-Depth Conversion > 2D...

Once here, you toggle 'Time to Depth' and select the Simple Time-Depth model  from the Z transform dropdown and press 'Create':

Fill in the values for Time and Depth and Save the file.

Complete the remaining fields, selecting the relevant data and naming the output.... press 'Run'.

If you then go to a New Depth Scene and select the model you have just created, OpendTect will display a second depth-converted scene into which you can load your data:

If you have mapped horizons, you can also use the Horizon-Based Painter (Simple).

Hoping this helps, alongside the other replies...

Kind regards,

Mark

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Kind regards,

Mark

Mark Crawford

Support Manager

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[Md Ariful Islam]

Hello everyone,

I created simple velocity model and horizon based painter for time2depth conversion. 

But when I open the depth data it is not shown like regular seismic data. its shown in solid color only (image od3). Does all depth section look like that? But I have seen depth section look just like time section. 

I used 1470 m/s velocity for water, 2300-3000 for sediments and 5500-6500 for crust. I got these velocities from another refraction study in this area.

Thank you everyone. 

[Paul de Groot]

Dear Ariful,

This is not what a depth section should look like. Please check if all horizons exist everywhere and that they do not cross each other. 

Best regards,

Paul.

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Paul de Groot

Geoscience Manager

-----------------------------------------------------------------------------------------------------------------------   dGB Earth Sciences
Phone: +31 53 4315155 E-mail: paul.d...@dgbes.com Internet: dgbes.com

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