# I was there when it all happened, a long time ago. Of course I was on the opposite side commercially. Time series limitations - Frequency domain methods.

## Presentation on theme: "I was there when it all happened, a long time ago. Of course I was on the opposite side commercially. Time series limitations - Frequency domain methods."— Presentation transcript:

I was there when it all happened, a long time ago. Of course I was on the opposite side commercially. Time series limitations - Frequency domain methods are currently accepted as seismic gospel. I point out some conceptual problems when it comes to inversion. The ADAPS approach - There are vast differences in nonlinear inversion approaches. ADAPS uses general optimization logic, analyzing large chunks of raw data in an iterative manner. Linear vs. non-linear inversion - Why linear systems stop short of true spiking, the distribution of information in the frequency domain and how non-linear processes can redistribute error. The glory of sonic log simulation - the need for intelligent detuning, the purpose of integration and the fallacy of power spectra after inversion. Matching to well logs verifies the inversion process - Sonic log images consist of integrated reflection coefficients and that is all we are interested in. If you can get me the pre-stack gathers I will give you a PowerPoint report. The birth of the frequency domain - Intelligent inversion opens exciting new interpretation possibilities - Click on an icon to enter topic The ADAPS offer - Untangling seismic tuning is the challenge we should focus on – just collapsing the wavelet is not enough!

Back before the digital era seismic filtering was analog and clumsy. Then an industry consortium came up with the time series mathematical concept that modeled time data by describing it in terms of frequencies, calling the required code a “transform”. Once there they found it possible to return to the original form with manageable error. This allowed filter design to be done in the frequency domain, where it was much easier. The industry fell in love with this beautiful concept and most researchers today seem to assume a seamless mathematical connection between the two extremes. When all this was happening, I had hired on with Western Geo. as manager of digital operations, with the responsibility of helping evaluate a time series package bought from the MIT team that was the heart of the mentioned consortium. For the life of me I could not see it doing any good. When the Western R&D boss proudly showed me a section where the deep half had been drastically changed, I was able to point out that the lower part was an exact duplicate of the top. Late, when I examined filters the package had designed, I found all the action always concentrated at the very front, which did not fit my idea of a system that could effectively remove side lobes. So I wrote the first predictive deconvolution in the time domain. It worked well enough to put Western first in digital processing, and they used it for years. I spent the rest of my Western time defending it against the time series researchers. It was a non-linear pioneer, iterating to improve the down wave guess, and the ancestor of my current ADAPS system. After two successful years I left Western as an employee and they hired one of the MIT experts to pick my brain (in terms of my time domain iterative program). I had been giving talks to geophysicists around the country, with no communications problem, yet the two of us did not seem to connect. It was not until the mathematical guru was able to put a few formulae on the board that progress was made. It was then I realized how different our thinking processes were. It was not just that I did not fully understand him, but that he could not think in my logical terms either. This is our real communication problem.

The glory of sonic log simulation - The first example, from http://adaps.com/a/nseafaults.pps, illustrates how bed thickness helped clarify a complex strike slip fault pattern. The stars mark a known shale that lies just above the target sands. In the show you can see the fault breaks develop. The fact that the obvious cross fault correlation did not seem to continue to the right of the green fault helped identify it as the main lateral movement feature in the prospect. While the existing interpretation saw it, the ancillary faulting (which I consider trapping) was not identified before ADAPS.http://adaps.com/a/nseafaults.pps The second, from http://adaps.com/a/examples.pps, shows an extremely probable reservoir at the upper left. The presentation illustrates how this lead was not visible on the input stack because of wave trap noise emanating from the bed. In any case the ability to make sense of the actual bed velocity enables this capability. Of course the need for intelligent detuning is the subject of the discussion.http://adaps.com/a/examples.pps

I’m not crazy about industry synthetics We can appreciate that rock physicist want to extract all sorts of attributes from seismic, but we are only interested in what actually creates reflections. While ADAPS does not want any help in the actual inversion process, we base its reputation on matching its output to well log information. I have been singularly unimpressed with the initial comparisons I have been given, all of which involved the generation of synthetic seismograms. In the first place I have little faith in the ability of current software to model the down wave that they use in the process. In today’s super whitened data these wavelets seem way too leggy. So, I ask either for finished sonic log images, or for velocities files. ADAPS has a module that computes reflection coefficients and then interpolates them, applying a low frequency averaging based on the observed wave lengths..

Does your data pass the smell test? Before you put too much faith in AVO or inversion results you should know. This type of wave trap generated noise is actually quite common, but one has to look. Before you start comparing inside-middle-outside trace stacks, a pre-stack analysis is helpful. Ikon Science has bought the proprietary rights to my software so I have none to sell. However I have the right to use my improved version on a service basis, a computer bank and an addiction for seismic exploration. The need to prove the merits of my creation is paramount, and I am willing to take all the risk looking at your data. If you can supply me with an adequate volume of gathers I will process enough to prepare a report. If you are happy with the results I will bill you \$5000 which you can opt to pay or not. Click here for noise discussion. Or here to see examples. Or here for a report example. Or for the site base. Or here to start over. Click on image to email me

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