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Using Radon Transform for Efficient Acoustic Wave Separation by Velocities in Wireline and LWD

IP.com Disclosure Number: IPCOM000199498D
Publication Date: 2010-Sep-07
Document File: 1 page(s) / 46K

Publishing Venue

The IP.com Prior Art Database

Abstract

This is a logical continuation (with certain improvement in some cases) of a previously submitted patent application on Hilbert Semblance: "Improved Accuracy of Acoustic Measurements For Reduced Receiver Array Apertures. Material on Radon Transform has been published by Rais Achmetsafin. It is well known that different acoustic wave components in the borehole acoustic logging (e.g. compressional, shear, Stoneley, tool mode, etc.) differ by frequencies, amplitudes, travel times, and velocities. Depending on applications, some of these components are considered to be informative, as others are detrimental. In some cases, conditions of wave propagation and certain tool design limitations don’t allow for distinct separation of these components without destructive interference between them. For the last 15 years, very good results were achieved in wave separation by using Short-Time Fourier Transform (STFT). Because of reversibility of this method, it first permits differentiating waves of different nature on spectrograms, with the respective “cleaning” of the signal converted back to the time domain. Unfortunately, simple time-frequency filtering does not solve all problems. For example, in case of a good cement bond of the casing the wave component that propagates through the casing attenuates very quickly. However, if the cement bond is poor the casing “rings”, and this ringing dominates the informative signal of interest, which propagates through the formation. The frequency separation is inefficient in this case, as the frequency content of these signals overlap. In this paper, we propose adding “time-velocity” signal representation to the traditional “time-frequency” consideration. The idea of separating wave components by their velocities is not a new one, and it is used for acoustic array data processing in the commonly adopted Semblance or similar processing techniques. By performing detailed systematic analysis, we demonstrate incremental improvement in the ultimate data quality when progressing from the traditional Semblance method to the improved non-windowed Hilbert Semblance, and finally to a special case of the Radon transform that is typically used in the computer tomography. We believe that the proposed approach can be adapted and efficiently used with certain limitations for different borehole acoustic applications.

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Title of Invention:

Using Radon Transform for Efficient Acoustic Wave Separation by Velocities in Wireline and LWD

Abstract of the Invention:

This is a logical continuation (with certain improvement in some cases) of a previously submitted patent application on Hilbert Semblance: "Improved Accuracy of Acoustic Measurements For Reduced Receiver Array Apertures. Material on Radon Transform has been published by Rais Achmetsafin.

It is well known that different acoustic wave components in the borehole acoustic logging (e.g. compressional, shear, Stoneley, tool mode, etc.) differ by frequencies, amplitudes, travel times, and velocities. Depending on applications, some of these components are considered to be informative, as others are detrimental. In some cases, conditions of wave propagation and certain tool design limitations don't allow for distinct separation of these components without destructive interference between them. For the last 15 years, very good results were achieved in wave separation by using Short-Time Fourier Transform (STFT). Because of reversibility of this method, it first permits differentiating waves of different nature on spectrograms, with the respective "cleaning" of the signal converted back to the time domain. Unfortunately, simple time-frequency filtering does not solve all problems. For example, in case of a good cement bond of the casing the wave component that propagates through the casing attenuates very quickly. However, if the cem...