| The dispersion and attenuation features of array acoustic waveforms are closely related to pore fluids,fractures and formation properties,etc.Accurate and effective extraction and application make the cognition of reservoir and surrounding rock characteristics clearer,thus realizing the efficient development of oil and gas.Based on the sound field simulation and mode wave feature analysis,the article compares in detail the influencing factors and performance of dispersion information extraction methods,studies the improved median frequency shift method for extracting attenuation features,and analyzes the application effect of the dispersion attenuation estimation algorithm.Firstly,based on forward simulation,the characteristics of waveform response under different conditions are analyzed,and the influencing factors of detection depth are explored.Secondly,combined with the measured and simulated data,the influencing factors of frequency dispersion algorithm are analyzed,and the amplitude preservation,resolution and noise immunity are compared.Then,the theory and realization idea of the modified median frequency shift method are combed.Finally,the application effect of dispersion attenuation algorithm is compared,and the combination of wave field separation and algorithm is proposed to extract the dispersion characteristics of porous strata with fracture zones.The results show that the reforming treatment can simulate the radial layered media with larger thickness.Weighted spectral semblance and Fourier transform method have good noise resistance,but poor amplitude-preserving performance and low resolution.Amplitude-phase estimation method has the advantages of accurate amplitude estimation,high resolution,but poor noise resistance.Capon algorithm has better comprehensive performance such as resolution,anti-noise and accuracy of slowness estimation,but the estimated amplitude is lower than the normal value.FBCapon combined with the wavefield separation of time domain filtering and frequency domain filtering based on the long and short time variance ratio method can better extract the dispersion features.The improved median frequency shift method can improve the accuracy of the algorithm by using the quality factor of known depth and averaging. |
