Potential of an electric field generated during the scattering of an elastic wave on a fluid-filled vug in a porous rock

Propagation of elastic waves in porous fluid-saturated formations is often accompanied by electromagnetic radiation (seismoelectric effect), which has an electrokinetic nature. The magnitude of the generated electric current depends on the velocity of the relative flow between solid grains and a liquid in the primary pores. When the elastic wave is scattered by an inclusion, an additional liquid flow is generated. This flow induces a supplemental electromagnetic field.In this work, we have calculated an additional electric field generated by the scattering of an elastic wave on the vug (spherical cavity) located in an electrolyte-saturated poroelastic rock. The solution of the corresponding electrokinetic equations was obtained in the quasi-static approach. We have considered the problem for "open" and "closed" interfaces between the porous matrix and the vug. The solution was obtained for conducting and non-conducting fluids in the vug. The dependences of the magnitude of the generated electric field on the frequency and the rock parameters are presented.The results obtained demonstrate that the magnitude of the generated electric field depends considerably on the parameters of the rock (porosity and hydrodynamic permeability), as well as on the parameters of the fluid inside the inclusion (electric conductivity and bulk modulus). The calculations show that for an open interface the amplitude of the generated electric field is larger by more than an order of magnitude than for a closed interface. This is because the amplitude of the filtration flow near the vug surface is larger.