Processing the Teapot Dome Land 3D Survey with Madagascar

Data Loading

The SConsruct file to download the Teapot Dome data from the Internet and convert to Madagascar format is in a separate directory to avoid unnecessary reruns. If you are working in a group it is best to get a copy of the data on a thumb drive to limit internet traffic. After getting a copy of the data on your computer you can comment the Internet download commands in the SConstruct file by adding a hashtag to the front of the lines stating with Fetch (do not miss commenting the continuation lines on the pdf files).

To view the data loading SConstruct script starting from your Teapot Dome directory, ($RSFSRC/book/data/teapotdome in the Madagascar download directory) type into a terminal window:

cd Fetchpaper
gedit SConstruct

Use an editor to look at the script. Make and updates (eg comment the Fetch commands) and update the file. To run the script, type:

scons

This will download about 11.4 Gbytes of data, mostly the two prestack traces segy format trace files. The file npr3_field.segy contains the unprocessed or raw field data with geometry loaded in the trace headers and npr3_gathers.segy contains the preprocessed data. On a good day downloading takes about 40 minutes using my home internet service and much longer if I am sharing a busy public network. The segy data is converted to Madagascar format (i.e. .rsf files) using sfsegyread. Each segy file creates a trace file and a trace header file. A summary list of a trace header files is created using the sfheaderattr program. It shows the trace headers contain fldr, tracf, iline,xline, offset, sx, sy, gx, and gy. These header keys are used throughout processing. The summary listing is used so often when building later SConstruct files that it is stored in a text file, fieldheaderattr.txt and included in some of the later SConstruct files. A detailed listing of some of the important headers can be created by running:

  
sftahread input=npr3_gathers.rsf  \
| sftahgethw  key=fldr,tracf,iline,xline,offset,sx,sy,gx,gy >/dev/null

followed with a quick control-c.

If you look carefully at sx,sy,gx,gy and offset you will notice the source and receiver (x,y) coordinates are scaled by 1000 to avoid rounding when stored as integers in the segy headers. Most seismic processing is done using (iline,xline,offset), but it may be necessary to scale the x,y coordinates before programs that use the source-receiver azimuth (e.g. azimuth dependent nmo, 3D dnmo, prestack Kirchoff migration).

The pdf file, 3dload_Teapot_Dome_3D.pdf, is downloaded and displayed. It describes “the processing grid” or “the four corners”, the relationship between the “real world” (x,y) coordinates and the (inline,xline) bin numbers. This is a critical parameter for binning, the process that computes and loads the (inline,xline) coordinates into the trace headers. These attributes are already in the Teapot Dome trace headers, but this information is almost always included with the seismic data because it is critical to connect the data to the physical world. Some program may require the four corners, and it is much easier to have them supplied than inferring them from trace headers.

The pdf file teapot_processing.pdf provides some basic information about the field parameters and the processing sequence. The field parameters may help you understand the geometry plots described in the next section. The processing sequence is typical for land seismic processing and include:

1. Refraction statics, which are often computed by the field crew.
2. Surface consistent amplitude and decon
3. Two passes of velocity analysis and residual statics

This paper recreates part of this sequence using Madagascar.

The PDF files and the headerattr print indicates processing units are feet. The PDF’s lists the bin size as 110 feet by 110 feet, group interval is 220 feet by 880 foot line spacing, source interval 220 feet by 2200 foot line spacing, and velocities. The dmo velocity field is downloaded and printed by SConstruct. It is good starting information about the stacking velocity and will be used later in the processing.

The final piece of information created in this directory is the segy text headers. The files are created by sfsegyread and can be listed to the screen with

cat npr3\_field.thdr 
or 
cat npr3\_gathers.thdr.

Processing the Teapot Dome Land 3D Survey with Madagascar