地层裂缝的各向异性横波传播特性实验分析

Experimental Analysis of Shearing Wave Anisotropic Propagation Characteristics in Fractured Formation

根据横波在裂缝性地层中传播所导致的分裂现象,在实验室利用声波探头测试裂缝性岩心的横波传播特性,分析横波的各向异性特征与裂缝宽度和裂缝方向的关系。通过实验分析,快、慢横波的幅度衰减及传播速度与裂缝宽度关系明显,且不同产状的裂缝对横波各向异性的影响具有明显的差异。实验发现,平行于裂缝延伸方向传播的横波其能量衰减明显小于垂直裂缝方向传播的横波,其速度要明显快于垂直裂缝方向传播的横波。随着裂缝宽度的增加,快横波和慢横波的振幅、传播速度随之降低,且它们之间的幅度差随裂缝宽度的增加而增大、传播时间差随裂缝宽度的增加而增大;水平裂缝对快、慢横波特性的影响要大于斜交缝对它们的影响。可以利用横波的各向异性特征有效地识别裂缝方向,从而为偶极横波测井资料在裂缝的检测与压裂效果的评价提供实验指导依据。

The formation generally forms artificial fracture when fracturing it.But fissured formation usually has anisotropic characteristics.On the basis of split phenomenon which is caused by S-wave propagating in the fissured formation,tested are propagation characteristics of S-wave about fissured core using acoustic probe in the laboratory,and analyzed is the relationship about anisotropic characteristics of S-wave and fracture width and fracture direction.Through experimental analysis,the relationship about amplitude attenuation and propagation velocity of fast-slow S-wave with fracture width are obvious,and the influence of various occurrence fractures on anisotropic S-wave has obvious divergence.The experiment shows that the influence of horizontal fracture on anisotropic S-wave is obviously greater than on that of oblique crossing fracture.With the increase of fracture width,fast-slow S-wave amplitude,propagation velocity decrease;The amplitude difference between them increase with the fracture width increasing,so does the propagating time difference.So the anisotropic characteristics of S-wave may be effectively used to identify fracture directions to provide experimental guidance criterion for dipole shear wave logging data in the evaluation of fractured examination and postfracture responses.