Dynamic streaming currents from seismic point sources in homogeneous poroelastic media

In a porous medium saturated with a fluid electrolyte, mechanical and electromagnetic disturbances are coupled, The coupling is electrokinetic in nature. The seismic waves generate relative fluid-solid motion that induces an electrical streaming current, Mechanically induced streaming currents generated by point sources in homogeneous, isotropic porous media are presented. The electrically induced streaming current is shown to be second order in electrokinetic coupling coefficient and is neglected, This decouples the mechanical behaviour from the electromagnetic behaviour with respect to the induced fluxes, We have used Blot theory to calculate the amount of induced relative flow by Green's function solution. The transport coefficients, conductivity, dynamic permeability and electrokinetic coupling coefficient, and their sensitivities with respect to porosity, DC permeability and frequency changes are evaluated. The conductivity decreases with increasing DC permeability. It has a k(0)(-1/2) dependence when grain-surface conductances dominate over the bulk-fluid-phase conductivity. Stationary-phase relative-flow and streaming current solutions are calculated for point sources acting on both phases of the porous medium. The streaming currents are induced by both P and S waves, The streaming current decreases with increasing fluid conductivity. This is consistent with the decrease of the diffuse double-layer thickness and zeta-potential, The porosity affects the bulk moduli of the solid. Its effect combined with the frame bulk modulus and compressibility of the saturating fluid determines the streaming current amplitude induced by a P wave. The increase in streaming current amplitude induced by S waves with increasing porosity is due to the decrease of the shear frame modulus with increasing porosity. The streaming current behaviour with respect to DC permeability is found to differ for sources applied to the elastic frame and volume-injection sources.