Presentation on theme: "Introducing the piggy back noise problem. This is what we saw visually on the 3D gather data. Strong and persistent +- 50 cps waves riding on very low."— Presentation transcript:
Introducing the piggy back noise problem. This is what we saw visually on the 3D gather data. Strong and persistent +- 50 cps waves riding on very low frequency random pulses. Practically invisible on an autocorrelation. One can see on the input slide that the desirable reflection info was invisible to the raw stack. The fact that the ultimate frequency determiner (the autocorrelation) could not even see a problem that was so apparent visually illustrates our dislike of frequency sensitive filtering. As we have often said, moving from time to frequency is a modeling process, and to describe this total wave combo requires many frequencies we do want to filter out. Lifting off two seemingly separate problems without disturbing the reflection signal is the challenge. To remove the high frequency reverberations automatically we first had to see them. We did this by moving to the first differences domain, and then designing a deconvolution procedure based on the autocorrelation. This routine was remarkably effective and it was easy to keep it concentrated at the high end. The low frequency pulses were so strong they controlled the stack. After a lot of study it was determined they were random (with no hint of long repeats), so the iterative routine for removing them used the stack as a control. They were examined individually to see it they hurt stack amplitudes, and, if they did their own amplitudes reduced. This was done gradually, to allow the stack to correct itself. Much visual checking was done in the design phase, to make sure the process was improving geologic believability. We urge you to repeat this last loop until you are comfortable with what has been done here. Click on the yellow oval to start. We can assure you that what you see is typical of the entire series. Handling background noise on the 3D volume thats the basis for our strike slip fault seminar- The text below describes our technique. The next 3 slides show the input, our optimization and the final ADAPS inversion and integration. The seminar – Our central message is seismic resolution. We were led to this topic through our interest in structural geology. Because we are proud of what our ADAPS tool does in improving resolution, we looked to structural situations where resolution is paramount. The problems associated with tracking parallel faults provide the best test proof we have been able to find. The structural situation itself is fascinating, of course, and the fact we can see faulting going on where we previously had no clue does excite us. For these reasons we undertook to build a very large folder which allows us to look inside a 3D interpretation. The techniques we ourselves use to track the faults are shown, with substantial comments. The folder is too large (almost 400 MB) to access via the internet, so we store in on our FTB site for you to download. Once there you enter the main show (accessfirst.pps), and then everything is quite fast. The name of the FTP service is adaps.exavault.com. Once you get there, it may ask you for the host, which is the same. The user is adaps and the password adaps1. The name of the folder you want to download is ADASplus. Please contact me at email@example.com with comments or firstname.lastname@example.org Click to study the original input stack, the optimized stack and the final inversion plus integration. Spend some time on this series.