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Interactive geometry analysis to build and check geometries effectively and efficiently - Land
Geom is an interactive front end application tool. Geom is used for picking first breaks and for geometry generation/verification. This is one of the first steps in the processing sequence. An accurate geometry is paramount to ensuring a high quality final product and, as a result, an excellent geometry program is important to both the processor and client.
With Geom, the processor can:
- Generate a geometry from the headers or from the observer reports
- Select straight or crooked line binning and compute fold
- Choose first break picking parameters and either auto-pick or manually pick the entire data set
- QC the geometry based on a comparison between the actual first break pick times generated by the computer and a user specified refraction function
- Edit any first break picks which require fine-tuning
- Update the geometry with the appropriate changes
- Output to file the updated geometry, first breaks and header information for use in other programs such as Generalized Linear Inversion (GLI)
DISPLAYS
Automatic First Break Picking and Geometry Correction
Straight/Crooked Line Binning
Maps
Automatic First Break Picking and Geometry Correction
A detailed description of Figure 1.1 follows:
First Break
This section shows the picks for the current shot displayed by offset with the refraction function overlaid in red. From shot to shot, this refraction function serves as an important QC tool in two distinct ways.
First, a correct geometry is quickly confirmed by observing the pick positions relative to the refraction function line. If the picks (in blue) are tightly grouped, not scattered, and closely follow the likeness of the refraction function, the geometry/patch has been correctly specified. A scattering of picks indicates a geometry problem which must be fixed by the processor. This is achieved by dragging location/patch/receiver line to collapse the scatter.
Second, for each shot, a QC value is calculated representing the difference between the first break picks and the corresponding times on the refractor function. The QC value is presented on a histogram plot for comparison with other shots. The processor must look for relative differences. Any values which deviate largely from the norm indicate a possible problem and must be investigated further.
Histogram
The Histogram display is used to select shots for analysis. As previously mentioned, any shot not closely matching the specified refraction function will be visible here and can be investigated by the processor.
Map
This display shows the position of the current shot and patch within the 2D line or the 3D grid (highlighted in blue).
Data
The current shot record is displayed with the first break picks in red and the user specified refraction function in blue. If required, the processor can edit first break picks in this window.
Straight/Crooked Line Binning
Once the geometry has been entered, a CDP line must be specified. In straight line shooting, stations are usually spaced at regular intervals. As a result, there is very little subsurface CDP scattering and CDPs are evenly distributed along the length of the CDP line. The CDP interval, fold and the resultant binning are very straightforward and easily determined.
However for crooked lines, special attention must be given to CDP binning. In the case of a crooked line, the inconsistent station interval and the curvature of the line results in a scattering of CDPs. In order to accommodate this scattering, several steps must be taken. First, an equal CDP interval is set or calculated and is forced on the crooked line. Next by adjusting the CDP line via a smoother, the processor works to obtain the highest most consistent fold along the crooked line.
The fold values along the line can be viewed at the top of the screen in the fold histogram. The surface location of the line is indicated in red. The yellow line represents the subsurface CDP line. The bin locations are represented by the short yellow segments which run perpendicular along the length of the CDP line. The blue dots represent the CDP scatter.
Maps
We have the capability of plotting the following types of maps in-house:
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