流体-孔隙介质界面震电反射和透射系数的简化表达式

Simplified expressions of seismoelectric reflection and transmission coefficients at a fluid/porous-medium interface

震电测井和海洋地震勘探中均遇到流体-孔隙介质界面.对于平面声波入射平面界面模型,本文利用前人给出的震电反射和透射电磁波的电场式,导出了震电反射和透射系数的表达式,其中声波与电磁波的物理参数是解耦的.在给定介质参数和入射角且已知三类弹性体波的透射系数时,就能通过该表达式计算震电反射和透射系数.该表达式对于所有入射角都是成立的,当入射角为复数时对应非均匀平面波入射的情况.利用电磁波数远小于界面切向波数的前提条件,将震电反射和透射系数的表达式化简为了简化表达式.简化式中与快纵波、慢纵波和横波有关的量均以透射系数与渗-固位移比的乘积形式出现,而动电耦合系数、电导率和渗透率以乘积形式作为一个整体出现.简化式表明,孔隙介质中的快纵波、慢纵波和横波通过渗流位移势影响震电反射和透射系数.数值算例表明,当平面声波入射角不是极其小时,震电反射和透射系数的简化式是适用的;快纵波对震电反射和透射系数的影响可以忽略.震电反射和透射系数的简化表达式不仅简化了震电波场的计算,而且明确表达了三类弹性体波引起反射和透射电磁信号的物理因素,为地下和海底储层的参数反演提供了思路.

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.