HR: 1330h
AN: NS23B-11    [Abstracts]
TI: Adaptive Power Spectrum Method for Processing Full Waveform Logs
AU: * He, F
EM: hefengjiang@vip.sina.com
AF: CNPC Well Logging Key Laboratory,Petroleum University of China, School of Resources and Information,Petroleum University of China, Beijing, Changping, 102249 China
AU: Tao, G
EM: taoguo@vip.sina.com
AF: CNPC Well Logging Key Laboratory,Petroleum University of China, School of Resources and Information,Petroleum University of China, Beijing, Changping, 102249 China
AB: The power spectra of borehole mode waves like compressional and shear head waves and Stoneley waves etc., are very important information from full wave acoustic logging data analysis. Conventional power spectrum analysis based on Fourier transform cannot derive such detailed power spectra because of none resolution in time domain. We have developed a new power spectrum analysis technique for full waveform acoustic array logs. Based on local cosine packet analysis and K-L transformation, this technique can diagonalize the correlation matrix of the acoustic signal. Meanwhile for the local stationary signal, the local cosine base is the best candidate of K-L transformation base. After the correlation matrix is diagonalized, the elements at diagonal represent the power spectrum of the signal. By arranging this procedure into an optimization procedure, we can thus determine the time window for each mode adaptively while calculating each individual power spectrum at the same time. The first step of the data processing algorithm is to decompose the whole signal with local cosine packet. And then the power spectrum of each component is calculated. Finally, we will find the optimum base with the local cosine packet tree. The objective function of the optimization is composed of the norm-2 of the power under certain base. Because the full waveform of acoustic logging is not an exact local stationary signal, the compressional and shear head waves are correlated. Therefore the STC method is employed to get the arrival time of compressional and shear head waves from the array waveform data, and then the shear arrival time can be taken as a constraint for this optimization. We have applied this method to a set of field full waveform logs. Our results have shown that the individual borehole modes are separated correctly and the power spectra for each mode agree with the existing theoretical predictions.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5102 Acoustic properties
DE: 5144 Wave attenuation
DE: 5194 Instruments and techniques
DE: 5199 General or miscellaneous
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly