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把地震互换原理应用于远源位移场,可推导出充满流体的井孔井壁上的入射平面波的质点位移公式。在长波长前提下,这种作用场是由作用在充满流体井孔的点力产生的。分析位移场可看出井孔对地震波传播的影响,这点对 VSP 测量尤为重要。当有效波的最短波长为井孔直径的25倍左右时,散射位移只与入射频率的一阶频谱和井孔直径成正比。当入射的 P 波垂直于井孔传播时,散射能量最大。用传输函数的概念来分析井孔对 VSP 测量的影响。如:波形畸变、振幅变化和时间延迟。当有效波的最短波长为井孔直径的40倍左右时,井孔对用锁壁式检波器做的 VSP 测量的影响可以忽略。88程
By applying the principle of seismic interchange to the far-field displacement field, the particle displacement formula of the incident plane wave on the borehole wall filled with fluid can be deduced. Under the condition of long wavelength, this kind of action field is generated by the point force acting on the well filled with fluid. The analysis of the displacement field shows the effect of borehole on seismic wave propagation, which is especially important for VSP measurement. When the shortest effective wavelength is about 25 times the hole diameter, the scattering displacement is only proportional to the first-order frequency spectrum of the incident frequency and the borehole diameter. The scattering energy is the largest when incident P waves propagate perpendicular to the borehole. The concept of transfer function is used to analyze the effect of borehole on VSP measurement. Such as: waveform distortion, amplitude changes and time delay. When the shortest effective wavelength is about 40 times the borehole diameter, the effect of the wellbore on the VSP measurements done with the wall-lock detector is negligible. 88 courses