Setup 2D/3D survey

To setup a new Survey (2D/3D) press New button in the survey selection window. The Survey setup window will pop up (see below) in which the survey parameters are specified.

It may be noted that the survey is setup to define the survey box. The key parameters are survey type and its respective coordinates. That can be entered either manually or by scanning a SEGY file.

Optionally, in case you have workstation access, you can get them from GeoFrame as well. Or if the OpendTect survey already exists, copy the coordinates by pointing the other survey.

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Note: In OpendTect, everything is tied to a 3D (X,Y,Z) with inline/crossline coordinate system. This is regardless of whether you have 3D data at all. Thus, for a survey which contains only 2D lines, a fake 3D survey box of inline/crossline system is needed. But on the other hand, if you want to use both 3D and 2D data, set up the survey according to the 3D cube.

3.1.2.1. Survey name and Type

The top most panel of the survey setup window defines two important things along with its disk location. The Survey directory name is entered in the first field. A directory with this name would be created in the root where you will save the OpendTect survey. The field for Full Survey name is filled with proper name of the survey that will be seen later on in the OpendTect survey selection window.

It is recommended that survey name and its directory name should be same as shown in previous

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figure of survey setup but different names can also be used without any problem. In third field select the location on disk where you want to save this survey.

The most important thing is the Survey type which can be Only 3D, Both 2D and 3D or Only 2D. The type is set accordingly:

• Only 3D is used when the survey contains only 3D cube(s).

• Both 2D and 3D is set when survey contains both 3D cube(s) and 2D line(s).

• Only 2D is set when survey contains only 2D line(s). And recalling the above note again: A fake inline/crossline system is defined to setup such survey regardless that 3D cube is not there.

3.1.2.2. Survey ranges

In the second panel of survey setup window the fields for Inline, Crossline and Z-ranges are filled with following possible ways:

1. Filling the ranges by scanning a SEG-Y file: Set the Survey ranges into Scan SEG-Y File(s) ->>.

The SEG-Y import window will pop up. In this window, select the input file/volume and press OK to start scanning the input file. After the scan is completed, the survey ranges will be filled automatically.

2. Entering Manually: If you already know the extents of survey ranges (Inline/Crossline/Z-range), just fill the maximum and minimum ranges and corresponding steps.

3. For 2D only: Set the Survey ranges into Set for 2D only ->> and press GO... The window will pop up (as shown below) in which the average trace distance (which determines the grid spacing of the 3D horizons) and the ranges for XY-coordinates are entered; Fill the

approximate values and press OK afterward. These parameters are survey characteristics to define the survey box. In the survey ranges the fake ranges for inline, crossline are

automatically set. Then fill in the Z range (no precision needed; 2D lines can stick out of the display box in all directions). The limit of the survey box will not affect the loading of 2D lines. The lines outside the survey area would be loaded normally. And that should be it.

Press OK and select the new survey.

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4. Get from GeoFrame: This option is used if you have workstation access to get the survey ranges from a GeoFrame project.

5. Copy from other Survey: Additionally, if the survey already exists, you can copy the ranges from that OpendTect survey.

3.1.2.3. Coordinate Settings

The relationship between inline/crossline and X/Y is setup generally by using this panel. The coordinates are automatically setup after scanning the SEG-Y file. You will only fill them if you are inserting survey ranges manually. Nevertheless, the three point (easy) method is not accurate

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because of rounding off errors which may not be 100% accurate. Both methods have been described here.

• In Easy mode, the coordinates are transformed by using three known points. Under Coordinate settings panel of Survey setup window, fill the inline and crossline and corresponding known XY-transformation as shown in figure of previous section.

• In Advanced mode, the XY coordinates are calculated by using an equation shown below.

The inputs required from user are origin (X,Y) and inline/crossline intervals along X/Y directions respectively. By checking the Overrule easy settings, the current easy settings would be overwritten.

The basic idea behind this has been elaborated in following figure:

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** The required inputs include origin X,Y pair, inline and crossline interval in both X & Y directions.

Note: If the provided coordinates are in feet, the Coordinates are in feet check box must be checked.

If the survey is a time survey and the Z-range units are set to milli-seconds (ms), you might want to display the depth in feet in the scene/annotations. For the later purpose the check box Display depths in feet should be checked.