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由于孔道的双电层结构和流体-固体耦合运动,弹性波在孔隙地层中传播时会引起电磁场.前人提出了基于这种耦合效应的震电测井方法,但对井中震电波的特性缺少细致的分析.本文对孔隙地层充流体井孔中点声源激发的震电耦合波的分波进行分析,证明了井孔流体电磁波波数不是井内震电波场支点,计算了地层电磁波支点、横波支点和快纵波支点对应的侧面波.在利用辐角原理求出震电波场函数的复极点之后,针对典型砂岩地层计算了震电波场模式波(包括泄漏模式)的频散曲线和声压、电场激发曲线.计算了各个侧面波和模式波的电场激发强度与声压激发强度的比值(电声激发比),发现纵波的电声激发比相对于横波和模式波更高,而Stoneley波电声激发比的辐角对渗透率敏感,其敏感性会随频率增大而增加,随孔隙度增大而降低.
Due to the double-layer structure and the fluid-solid coupling movement of the tunnel, the elastic wave will cause electromagnetic field when it propagates in the pore formation.Previously, the method of electrokinetic logging based on this coupling effect has been proposed, but the characteristics of the seismic wave in the well are lacking This paper analyzes the sub-wave of the electromechanical coupling wave excited by the mid-point sound source in the borehole of the pore formation, and proves that the wave number of the fluid in the borehole is not the fulcrum of the wave field in the well, and the electromagnetic wave fulcrum, And the fast longitudinal wave fulcrum corresponding side wave.After using the principle of argument to find out the complex pole of the seismic field function, for the typical sandstone formation of the seismic wave mode wave (including leakage mode) the dispersion curve and the sound pressure, the electric field Excitation curves were calculated.The ratio of the electric field excitation intensity to the sound pressure excitation intensity (electroacoustic excitation ratio) of each side wave and mode wave was calculated and it was found that the electroacoustic excitation ratio of the longitudinal wave was higher than that of the transverse wave and the mode wave, The excitation angle is sensitive to permeability and its sensitivity increases with increasing frequency and decreases with increasing porosity.