基于EMD的声波测井信息提取与火成岩裂缝地层特征分析

火成岩储层中发育的裂缝具有不同的性质,可以采用声波测井资料进行评价。首先通过经验模态分解(EMD)将火成岩裂缝地层的阵列声波测井信号分解为多个具有瞬时频率的平稳信号——固有模态函数(IMF)分量,每个IMF分量代表声波测井信号中不同组分的波,即纵波、横波和斯通利波等;然后通过Fourier变换将时间域的IMF分量转换到频率域,一定程度上改善了非平稳声波信号Fourier变换的局限性;最后通过对比、分析特定IMF分量的能量、主频和到时变化规律,得到各组分波对中低角度裂缝、高角度裂缝、网状裂缝和半充填缝的响应特征。将该方法应用于辽河东部凹陷火成岩裂缝地层特征分析,结果表明:纵波、横波和斯通利波的高频成分对裂缝普遍敏感,具体表现在到时、主频和能量三个方面的变化上,敏感程度与裂缝的角度有关。一般地,裂缝的倾角越大,声波受到的影响越小,其中斯通利波对裂缝的响应最明显,横波对裂缝的敏感程度要强于纵波,纵波对高角度裂缝一般没有明显响应。

The fractures developed in unconventional reservoirs have different properties.The array acoustic logging signals in volcanic formation are decomposed into stationary signals with instantaneous frequency (IMF) using the EMD method.Each IMF represents different component of the original array logging signals,including compressional wave,shear wave,and Stoneley wave.Then,IMF is converted from the time domain to the frequency domain by Fourier transform,to overcome the limitation of the non-stationary acoustic wave to Fourier transform to some extent.The response characteristics of mid-low angle fractures,high angle fractures,reticulated fractures,and semi-filled fractures are obtained by comparing the variation of the wave energy,main frequency,and arrival time of each component.The results of EMD decomposition of fractured volcanic formation in the eastern depression of the Liaohe oilfield indicated that,the high frequency components of compressional wave,shear wave,and the Stoneley wave are sensitive to the fractures,manifested in terms of the arrival time,main frequency,and energy.Their sensitivity is related to the angle of the fractures: the greater the dip angle of fractures,the smaller the influence of acoustic waves.Among them,the Stoneley wave showed the strongest response to fractures.The shear wave was more sensitive to all kinds of fractures than the compressional wave,and the compressional wave usually had no obvious response to high angle fractures.

国家重点基础研究发展计划(973计划)项目(2012CB822002)和国家自然科学基金项目(41874135)共同资助。