GLOBE Claritas seismic data processing: Seismic Geometry Definition

The Claritas geometry application is used to control 2-D or 3-D seismic survey geometry information. Text files (containing the observers logs, navigation files or topographic survey) are input to the geometry application, which is used to create a geometry database, and wiggly line CDP gathers or 3-D bin definition. The input text files can be easily created from whatever ASCII format input data is available, using a suite of filter programmes. Alternatively, the geometry database may be created from the header information in SEG-Y trace headers.

The Geometry application can be used to :

- Display a map of the peg and shot XY and height information
- Display a 3-D isometric view of the survey pegs and shot-holes
- Create land and marine geometry databases
- Define a wiggly-line or 3-D grid by picking hitpoints with the mouse
- Calculate linear, wiggly-line or 3-D CDP gather geometry
- Display trace midpoint and azimuth distribution, and CDP bins
- Show the CDP-fold variation as colour-coded bins, or a histogram
- Calculate and display floating-datum elevation statics
- Present information listing shot, trace or CDP statistics
- Produce hardcopy graphical output

To define a 2-D wiggly-line CDP gather, the user clicks on the map of trace mid-points to define a set of hitpoints; the CDP positions are then positioned along a spline fitted to these points. Since the trace mid-point map is colour-coded by source-receiver offset, it is simple to position the CDPs to take advantage of the optimum offset range for the seismic data. 3-D grids are defined using three hitpoints. {geom3d.tif}

Geometry information may be applied to seismic data using the ADDGEOM processor module; the CDPSORT or DISCSORT modules may be used to effect a CDP-sort at any point in a seismic processing flow. Alternatively, the DISCGATH processor may be used to read a shot-sorted disc file and output CDP-sorted gathers, effectively dispensing with the need to store CDP gathers at any stage in the processing sequence.

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