[OpendTect_Users] Creating a 3D horizon from 2D seafloor picks

[Paul de Groot]

Dear all,

The preferred way of mapping horizons in OpendTect is via the Volume
tracker and not by mapping lines in loose grid. The latter method is
standard in most other packages, which I assume puts many people on the
wrong track when trying to map horizons in OpendTect. We do support
tracking on a line-by-line basis but once you have mapped this loose grid
of lines it becomes a bit tricky to get a decent horizon out of it. You can
grid it in OpendTect but as we saw earlier this week in another discussion
in this forum that is not so straightforward either. In other packages you
would then launch a batch auto-tracker to fill in the gaps. In OpendTect we
do not have a batch auto-tracker but we do have the interactive Volume
tracker option that can be used to fill in the gaps. This brings you back
to my first sentence: since you have to use the volume tracker anyway, why
not use it from the start (if the data allows this).

Sea-bottom reflections are often so strong that you may be able to run the
volume tracker from one seed position only with almost no editing required
afterwards. The controls for the volume tracker are set in the tracking
toolbar. The idea behind the volume tracker is this:

   - You position a box around the horizon you want to map. OpendTect loads
   the data in this box data into memory (the size of your box depends on the
   memory you have and on how much you can auto-track without too much
   editing).
   - You pick a seed and press the volume track icon: the horizon is
   auto-tracked in the box.
   - You QC the horizon by movie-style moving inline & cross-line sections
   through the box. Toggle the "display horizon on sections only" icon to on!
   - Where needed you edit the horizon by cutting out parts where the
   tracker went off track, and filling in the removed part by re-tracking (use
   volume tracking, line tracking, or manual tracking where needed).
   - When you are satisfied move the box to the next area and repeat the
   exercise until the entire horizon is tracked.

Note that if you have a HorizonCube license you can also run the
dip-steered tracker to track individual horizons from a steering cube. One
advantage of this tracker is that it can stop against mapped fault planes.

I hope this helps. Best regards,

Paul.

-- 
*Paul de Groot
President
dGB Earth Sciences, Nijverheidstraat 11-2, 7511 JM Enschede, The
Netherlands.
Tel. +31 53 43 15 155, Fax +31 53 43 15 104.
paul.degroot at dgbes.com, www.dgbes.com, www.opendtect.org.

*
On Fri, Oct 5, 2012 at 9:42 AM, Neil Peterson <neil.peterson at gradient.com>wrote:

> Hello,
>      I had a similar issue. I was mapping the top of basement granitic
> rocks and tried what you are talking about. The way I ended up getting the
> horizon was to complete the interpretation of basement top on all 22
> seismic lines in the available grid (using 2D horizon/draw between seeds
> with interpolate on).
>      Once this was done, I individually exported the x, y, z info for the
> seeds on each line and created a single file of all x, y, z points (copy
> everything into one notepad file).  Then bring in as a Horizon/3D geometry.
>      I then gridded the file using a calculated grid node spacing over the
> project area and 200m search radius/grid spacing. This may be the long way
> around the problem, but it worked. You'll definitely need more than one
> line to do this.  Otherwise all that you get with deriving the 3D surface
> the way you tried will be a small plane extending a short distance on
> either side of your picked horizon.
>
>      I hope this helps and good luck with your project.
>
>
>
>
> Best Regards,
>
> Neil Peterson | Senior Geologist | Gradient Resources Inc | 9670 Gateway
> Dr. Suite 200, Reno NV 89521 | ph: 775-284-8842 | cell: 775-217-2629 |
> email: neil.peterson at gradient.com
>
>
>
> On Oct 4, 2012, at 7:19 PM, "Katable" <katable at gmail.com> wrote:
>
> > Hi there!
> > We are a postgraduate class using opendTect for the first time to
> interpret seismic lines, we have just gotten started on trying to pick the
> seafloor before moving on to interpret other horizons in the survey.
> Unfortunately we are having trouble creating a 3D seafloor from our 2D
> picks. The method we have been trying to use is: in the main window under
> the 2D horizons tree: right clicking on a horizon and selecting derive 3D
> horizon and then trying to either extend or use other picks to derive a 3D
> seafloor. At this point the computers crash and we have to close the
> programme. Is there a better way/a way around this problem.
> > If anyone has any suggestions please let me know.
> > Thanks,
> > Geophysics 780 class from Auckland University
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