Marine Multi-channel Seismic Data Processing (part-1)

I think it is time for ProMAX right now. What is ProMAX? It is a software package of Lankmark Graphics Corporation since 1989 of Halliburton, for processing reflection seismic data. It is commonly used in the energy industry. Is it free? Unfortunately not! Even kind of expensive when comparing to other programs that will do the same sort of thing like SIOSEIS. Also another unfriendly thing for ProMAX may be that it runs on flavors of UNIX like Red Hat (but note that: not all the UNIX system can make ProMAX work), and I guest most people would like Windows-based program, because they hate command lines and writing script! But the good thing is, ProMAX is a program of user interface! No writing script. Gi'gem! You just need to start ProMAX in the terminal, and then you will use the program as friendly as Windows.

OK, let us get down to the technical business. What we are doing for processing the marine relection seismic data on the boat are following some workflows:

(1) SEG-D data input
When we get the raw shot data tape by tape from the recording system on the seismic boat, they are in SEG-D format and every .RAW file stored in the tape stands for one single shot gather (one shot point with 468 channels & traces). We probably get 3 tapes of raw shot gathers per day, which are about 18 GB each with maximum 1273 .RAW files in one single full tape. Even we have SEG-D data immediately when the boat is investigating, but we do not have much things to do until we finish the whole single seismic line, because we need the processed navigation file in .p190 format to set up the geometry for following processing work, and the .p190 files just can provided at least after completing one whole seismic line (sometimes after several short lines they process several .p190s together to save money on the use of lisence of the program). However, we still have things to do: we could take a first look at the raw shot gathers (ProMAX module: Trace Display), to find out the overall situation including direct wave path, reflected ray path including primaries and multiples, noise and bad channels; we can also figure out the main frequency range (PromMAX module: Interactive Spectral Analysis); and we could also make a near-trace plot by only using the near group of every shot to show the first glimpse of geology. We can have a first basic look at the major horizons like sediment layers, transition layers, volcanic layers or acoustic basement. Scientists are willing to see the seismic image as soon as possible. So the near-trace plot is a good thing to show them to release their desire in real time.

(picture below: near-trace plot of MGL1004 MCS line A)

(2) Set up Geometry
When we get the .p190 files for the seismic lines, we are ready to start the whole process flow. The first thing we need to do is to set up the geometry (ProMAX module: 2D Marine Geometry Spreadsheet). A lot of information we need to provide to ProMAX: group interval(12.5m), shot interval(50m), sail line azimuth, source depth(9m), streamer depth(9m), shot point number, source location (easting-X and northing-Y), field file ID, water depth, date, time, near channel number(468), far channel number(1), minmum offset, maximum offset, CDP interval(6.25m), full fold number(59), etc. Anyway, a lot! It takes some time to fill out the sheet and we need to be careful to make sure all the information matching up together. Sometimes it will be tricky, so double check, even triple check!

(3) Load Geometry
When the geometry set-up or the Spreadsheet is done, we can load the geometry in the raw shot data (ProMAX module: Inline Geometry Header Load). It takes time! Remember every tape is 18 GB. It will take almost one hour for loading one tape in (maybe faster using better workstation). After loading all the tapes or all the raw shot SEG-D files in the ProMAX with the geometry, they are ready to go to the real part of processing. Hold on for a second. I say "real" here, because I mean we are starting to polish the raw data, i.e., where change happens!

(picture on the left: ProMAX geometry assignment map)

To Be Continued, next week, part-2!