Geometry QC Package

 

The primary goal of Geometry QC is to ensure that source and receiver coordinates are accurate and consistent with the seismic data. This can be performed in the field or after the survey. If performed in the field, all bad points should be re-surveyed (when possible). After the survey, the recomputed coordinates will give an approximation of the actual position. A valuable product of using SeisNav Resolve for Geometry QC is creation of merged SEG Y files, i.e. the seismic data is in standard SEG Y format where the trace headers contain coordinates and elevations from the survey data as well as computed values such as offset and source/receiver azimuths and complete binning details. The value in this product is that these SEG Y files can be input directly into ProMAX and/or other processing systems for complete processing starting with 3D DMO. Note that some Geometry QC can be performed without merging the seismic data, however, the total QC results are far superior when merging is done. Results from all QC tasks listed below can be displayed in a professional format to depict problems and/or solutions. Tasks that should be performed include:

  • View coordinates overlaid on a topography map (if applicable, we support TIFF and GIF image formats and have tools for graphically splicing images and registering them for the coordinate overlays). Verify the elevations. Overlays will also show the reasons for many changes to the shot or receiver layout. The topography maps may be obtained and scanned during the position surveying, and the first coordinate overlays should be made with the preshoot survey data.
  • At the preshoot stage, or any other time during the survey, the survey data may be binned. Examine the offset distribution cube, and generate aerial slices at different offsets to look for holes in coverage. Skipped surface locations are accurately imaged at depth. Generate a "TIME VARIANT FOLD" data volume in SEG Y format. Examination of time slices of fold at important prospect horizons can be achieved. Evaluate the need of infill shooting. These displays are generated with a representative velocity function and a suitable muting scheme.
  • Comparison of coordinates against a preshoot data set. This will highlight gross coordinate errors as well as missing nav/survey data.
  • Verification of cable separation along a receiver line. If the cables only have a small amount of slack, certain separations are physically impossible.
  • Create surface displays of the coordinates in separate maps to verify consistency between source and receiver elevations. Color-coded flat map can also be used for this comparison. Many times in land or OBC jobs, the sources and receivers are surveyed separately. Thus, near receiver and source positions should be consistent in all three directions (x,y,z).
  • Merge survey data and binning information into trace headers of seismic data. This step is for checking and resolving Observer Log discrepancies and survey data problems. View traces with a computed first break time (based on computed offset, a near surface or water velocity and a system delay time) overlaid. This should be performed for both shots and receivers separately. This merge data can be saved to tape to provide a head start on processing.
  • View the merge in the "Shooting Nav" or "2D Edit" display to see geometry and seismic on the same screen. These are good tools for visualizing how the seismic traces reflect bad geometry. LMO (linear move-out) may be performed inline with the "2D Edit" display for viewing as "flat plots".
  • Recompute coordinates (in batch mode with the Residual Nav processor or interactively with Geometry Workshop) for any points (sources or receivers) which seem bad. This recompute should be verified against the seismic to ensure improvement. In the "Geometry Workshop" display, the user can interactively pick first breaks and recompute coordinates and see the adjusted computed first breaks based on the new coordinates.
  • Create a near-trace cube to verify coordinate consistency.
  • Perform a brute stack to further verify coordinate consistency. A brute stack should be performed before and after applying recomputed coordinates to the data to make sure there is improvement. This process also generates time variant fold or time variant average offset, which may be displayed separately or overlaid on the seismic.

 

Binning QC Package

 

The binning provided in SeisNav Resolve can be used before or during production to analyze a survey. When a survey is being designed, users will get binning and coverage analysis to help achieve the desired offset and azimuth results. During shooting, the software can show the effects of moved shots and receivers on coverage. Binning features include;

  • Processing and analysis is provided by the ‘Binning’ module. This provides the following binning features for nav data without regard to the seismic:
    • Computes a redundant and non-redundant fold for each bin. These show coverage of the survey area.
    • Compute a series of folds inside each bin according to a distribution key. This can be used to compute an offset-variant fold to view coverage at all offset levels. Azimuth’s could also be analyzed to see the coverage in different azimuth ranges.
    • Compute the minimum, maximum, or average value of any attribute inside each bin according to a distribution key. In the above example, instead of offset-variant fold, create an offset-variant average azimuth.
    • Compute the time-variant fold that should be provided by this data given a velocity function and muting scheme.

     

  • During a merge of the seismic data and navigation coordinates, binning is performed. The CDP, inline, and crossline numbers are computed. Binning attributes computed are CDP deviation, source/receiver azimuth, and offset. The x and y coordinates of the center of the bin is also stored in the header.
  • The ‘Binning Displays’ are devoted to displaying the output of the ‘Binning’ module. This display draws one box for each bin in the display. Inside this box can be a histogram or a spider plot based on the SEG Y data output from the Binning module. The histogram should be used to view a histogram of information pertaining to the bin. For instance, if you run an OFFSET header stack, the picture will tell you the total number of traces in this bin at each of your specified offset ranges. The spider plot could be used to look at min/max/average source/receiver azimuth within the bin.
  • Viewing the binning information using other SeisNav Resolve displays is quite simple and useful. The information produced by the ‘Binning’ module will read directly into any of the displays. Fold maps can be created as a 2D flat map, 3D surface, 3D histogram, or even overlaid on a topography map to see physical reasons for coverage changes.
  • LOSSLESS compression of large P1/84 and P1/90 navigation files is available to assist in reducing system requirements. Typical compression ratios are 50:1 to 60:1. The other attraction to our compression is that our ‘Binning’ module can read and process the compressed files.
  • A number of survey file utilities for comparing and manipulating SEG P1 and SPS files are also available.

3D Velocity QC Package

 

The Velocity QC provided in SeisNav Resolve can be used during production velocity picking/analysis or after to build cubes for analyzing velocities over a entire survey. Additionally, inputting velocities used to process data from 2D surveys in the area and building a velocity cube, can be useful in the design phase of a 3D survey as well as giving a good start on brute stack velocities for in field processing. Velocity QC features include;

  • Input of various ASCII T/V pairs file formats, e.g. Tensor, ProMAX, Geco, Western, …, linearly interpolating in time and in space for the control point key, and outputting a SEG Y format file with the trace data containing the velocity functions. At the same time as T/V pair input, a matching horizon file with up to 8 horizons may be input and output in the SEG Y trace headers. The trace interpolation processor will allow linear interpolation between pairs of control points in either the crossline or inline directions for filling in the velocity volume. Option processing would include;
    • Converting RMS velocities to interval or average velocities with the velocity processor.
    • Filtering the velocities using the iterative filter processor.

     

  • The Velocity Edit Display gives viewing and editing capability of the control points defining a 2D velocity field. The display also shows both RMS and interval velocities as well as overlaying horizons from a file or the trace headers. ASCII T/V pairs files may be input directly into this display, and editing may be saved to another file.
  • The Profile Display allows multiple views of the velocity data as a two dimensional graph, a three dimensional histogram, or a three dimensional surface.
  • The 2D Display supports viewing 2D velocity fields in a color display. It also allows for viewing seismic data with a color coded velocity field underlaid and/or multiple horizons overlaid.
  • A velocity volume may best be examined for consistency in all directions using the Cube Display. An interesting feature of this display is a 3D animation through one or more velocity isosurfaces.
  • Since the velocity data is output as SEG Y, the files may easily be input into other seismic processing software packages for processing or display.