流体-孔隙介质界面震电反射和透射系数的简化表达式

Seismoelectric logging and marine seismic exploration involve the fluid/porous-medium interface. For the model of a plane acoustic-wave incident on a plane interface, the expressions of seismoelectric reflection and transmission coefficients at the fluid/porous-medium interface have been derived by using expressions of reflected and transmitted electric fields given by earlier authors. The physical parameters of acoustic waves and electromagnetic waves in the expressions are decoupled. Given the medium parameters and incident angle, and the transmission coefficients of three types of elastic body waves are known, the seismoelectric reflection and transmission coefficients can be calculated directly by these expressions. The expressions are correct for all incident angles, where complex angles correspond to the incidence of the inhomogeneous plane wave. We simplify the expressions of seismoelectric reflection and transmission coefficients by using the condition that electromagnetic wavenumbers are much smaller than the tangential wavenumber at the interface. In the simplified expressions, the quantities related to fast compressional, slow compressional and shear waves all appear in the form of the product of the transmission coefficient and the ratio of seepage to solid displacements, and the electrokinetic coupling coefficient, conductivity and permeability appear as a whole in the simplified expressions. The simplified expressions are correct when the incident angle is not extremely small. The simplified expressions show that fast compressional, slow compressional and shear waves affect the reflection and transmission coefficients through the seepage displacement potential. The influence of the fast compressional wave on the seismoelectric reflection and transmission coefficients can be neglected. The simplified expressions not only simplify the solution process of seismoelectric wavefields, but also clearly show the factors that three types of elastic body waves cause reflected and transmitted electromagnetic signals.