[Users] Using 2D data - an introduction

[Bert Bril]

Dear users,

For a support question I've put together a little 'HOW-TO' for 2D
seismic data.


(1) Setting up the survey

When you set up the survey you can choose either 'Only 2D' or 'Both 2D
and 3D'. In the 'Both' case, set up the survey as you would have done
for the 3D situation. If it's 'Only 2D', life is simpler. Select 'Set
for 2D only' and press 'Go'. You need to specify coordinate ranges and
an average trace distance. No need to be precise there, 2D lines may
'stick out' of the survey boundaries, the average trace distance is of
limited importance so just type a nice round number. After this,
OpendTect will have calculated an inline/crossline range and coordinate
transforms. The thing is that OpendTect is totally 3D, and there will
always be inline/crossline. Only, for 2D these will only be used 'under
the hood'. Specify the Z range correctly.

If you don't know these things off hand, you can first scan a SEG-Y
file. Select 'Scan SEG-Y file'. But remember what you are doing: don't
think you can set up the survey with it: that only works well when the
SEG-Y file contains 3D cubes. Still you'll get a useful scanning report
with coordinate ranges, data values and so forth. It will stay on the
screen after you've canceled out of the dialogs underneath.


(2) Importing the data

You can import data from either SEG-Y or 'simple file'. I guess 99% of
the loading not via the ArkCls workstation access plugin will be SEG-Y.
When importing the data, you have to remember that OpendTect expects the
data to be fully processed. So, navigation data in separate files - not
usable. The coordinates have to be right in the SEG-Y headers. You just
need to point out where the correct byte locations are. If you're lucky,
your SEG-Y data is REV. 1 compliant - then setting up the SEG-Y
definition is easy.

Similarly, OpendTect needs *one* identification number for each trace.
You can choose what that will be: CDP number, shot point number, ... as
long as this number is well-behaved (i.e. nicely going up or down) you
can use it. It will be your identification too, in various displays.
When exporting data later, this number will be available, no other numbers.

The destination of the import is a 'Line Set'. This is how lines are
grouped in OpendTect. Like so often, the choice on how to group lines or
even copies of line sets is completely up to you. So for example if you
have data from 2 different 2-D surveys (e.g. from different years) you
could put those in two different line sets, or not - we don't care.
Later, you may want to filter your data and put the filtered lines in a
new line set.


(3) Displaying the data

After the import, you see nothing until you ask for it. So, right-click
on the '2D Seismics' and do 'Add'. Open a (or the) line set. Select one
or more lines. At first, OpendTect will load the line geometry only, so
this is quite quick. Most people therefore simply select all lines in
the line set at this stage. Now, the lines should appear in gray in the
3-D scene. If they don't, then something has gone wrong during import.
By far the most common reasons are bad coordinates or bad trace numbers
(which then screw up the sorting of the traces).

To see some seismics you have to right-click in the tree. Every line
will already have one 'attribute' attached to it, you just need to
right-click on it and select your data to make OpendTect load and
display it. If at this point in time you do not see seismic data on the
line, the two most common reasons are:
* The data is bad. Go with your mouse over the line and check the data
values.
* If the data is OK (i.e. you see nice seismic values when your mouse is
 on the line) then you probably have a problem with your graphics card.
Old cards, old drivers are common, also try to disable shading in the
Utilities-Settings-Look&Feel dialog. We may be able to help, you may
need to buy a good graphics card.


(4) Using the data

Now we are ready to create attribute sets, do tracking, or what else you
may want to do. I won't go into details here, but the following may be
good to know:

* There is no way to import 2D horizons at the moment. The biggest
problem is an infinite number of possible formats, and no standards
* You cannot set seed points for the tracking in the flat viewer (yet)
* If you want to use 'Steering' (e.g. you have a license for the dGB
Dip/Steer plugin), note that you can only have one 'Steering' attribute
in 2D. If you want to have alternative steering data, you have to use
multiple line sets.



Bert

-- 
-- Bert Bril / OpendTect developer at dGB
-- Nijverheidstraat 11-2, 7511 JM Enschede, The Netherlands
-- mailto:Bert.Bril at opendtect.org , http://opendtect.org
-- Tel: +31 534315155 , Fax: +31 534315104