【摘要】 为了研究裂缝性火成岩地层中纵波和横波的时频特征,联合经验模态分解(EMD)和分数阶Fourier变换对阵列声波测井信号进行滤波。首先通过EMD得到高频的IMF,再利用分数阶Fourier变换的旋转特性分离高频IMF中的纵波和横波,得到不同角度裂缝对应的纵波和横波Choi-Williams分布。结果表明:联合EMD和分数阶Fourier变换能有效改善纵、横波的时频耦合;相对于致密地层,裂缝性火成岩地层中的纵波和横波均幅值衰减、主频降低,同时速度减小。一般地,纵波幅值衰减与裂缝倾角呈正相关,横波幅值则相反;对于低角度裂缝,横波比纵波更敏感;纵波和横波主频在低角度裂缝和高角度裂缝地层中的差别不大;纵波和横波的速度在穿过低角度裂缝后降低更严重。更多还原

【Abstract】 In order to study the time-frequency characteristics of the primary wave(P wave) and shear wave(S wave) in fractured igneous formation, array acoustic logging signals are filtered by combining EMD and fractional Fourier transform. First, the high-frequency IMFs are extracted from the array acoustic signal by the EMD, and then the P and S waves are separated by using the rotation of fractional Fourier transform. Finally, the Choi-Williams distributions of P and S waves corresponding to different angle fractures are obtained. The results show that the joint EMD and fractional Fourier transform can improve the time-frequency coupling of P and S waves. The energy, dominant frequency and velocity of P and S waves in fractured igneous formation are lower than those in tight formations. Generally, the higher the dip angle of fracture, the greater the attenuation of P wave energy and the smaller the attenuation of S wave energy. The dominant frequency of P and S waves has little difference between low angle fracture and high angle fracture. The velocity attenuation of P and S waves is stronger after passing through the low angle fracture.更多还原