Rock classification according to seismo-electric and electrokinetic effect occurrence

The seismoelectric effect and the effect of induced polarization of the electro-osmotic type belong to the category of electrokinetic phenomena. The theoretical foundations of both effects are based on the Helmholtz – Smoluchowski equations applied to streaming potentials and electro-osmosis. However, electrokinetic phenomena of significant amplitude do not occur in every type of rocks. Using the mathematical concepts of M. Biot who regarded the fluid motion relative to a solid matrix for slow seismic waves in the wave equation and R.N. Chandler’s problem on transient pressure inside a pore, the amplitude of seismoelectric effect in porous rocks has been calculated. The purpose of the study is to present the analysis results of the amplitudes of electrokinetic effects that occur either when a pressure gradient is imposed on the rock or when there is a potential difference, based on F. Gassman’s classification of the relationship between the components of distinguishing rocks with perfect, imperfect and absent connections between the phases. It has been shown that seismoelectric effect does not occur in rocks with no bonding between the components, where the pore filler freely circulates in the pore space and pores are well connected to each other. The rocks with perfect connection also feature no motion of pore moisture as a result electrokinetic phenomena in these rocks are suppressed. The seismoelectric effect and electroosmotic phenomena occur only in the rocks with imperfect bonding between the components (rocks with low, medium and partially high permeability (except clays)) with the pore radius of 1·10 -6 – n ·10 -4 m. The effects of induced polarization distort TEM signals and can be detected only at the values of the induced polarization decay constant of ~ 1 μs – n ms.