【摘要】 采用优化高阶差分法模拟计算了裂缝性地层中的井孔声场 ,分析了低频情况下单裂缝、双裂缝、裂缝宽度以及声源主频对瞬态波场和声波全波列的影响 .结果表明 :在低频情况下 (≤ 3kHz) ,声波的反射系数会随裂缝宽度以及声源主频的增大而减小 ;双裂缝在声源条件相同的情况下 ,若裂缝间隔不大 ,其低频反射波幅度相对双倍宽度的单裂缝要小 ,但经过双裂缝的作用后 ,不仅透射波场波的能量会发生衰减 ,而且传播频率也会发生变化 ,特别是在裂缝附近 ;当声波以不同的角度入射到波阻抗界面上时 ,所造成的声波反射会随之变化 ,入射角越大 ,反射系数越小 .更多还原

【Abstract】 In this paper, the acoustic field in a borehole is simulated by means of the optimal high-order finite-difference method in fracture formations; and the effect of single or/and dual fracture, the width of the fracture, and the center frequency of source on the instantaneous wave-field and the full waveform are studied. The results show that in low frequency(f≤3 kHz), the reflection coefficient of acoustic wave decreases with the increase of the width of the fracture and the center frequency. For dual-fracture, the amplitude of reflected wave is less than that of the single fracture with doubled width for the same source. Because of the influence of the dual-fracture, not only the energy of the transmission wave attenuates, but also the frequency alters, especially near the fracture. In addition, when the incident wave impinges upon an acoustic impedance interface at different angle, the wave reflection will change accordingly, what’s more, the greater the incident angle is, the less the reflection coefficient is.更多还原