![]() Second, the electrokinetic scattering matrix for a fluid/porous-medium interface is derived. ![]() First a straightforward scattering problem of an incident fluid P-wave into fluid electromagnetic and pressure waves, and porous medium waves is considered. Subsequently, the wave coupling at a fluid/porous-medium interface is theoretically solved, where the modified theoretical formulation is applied. When the coupling coefficient is zero, the electrokinetic equations decouple into the familiar Biot’s poroelastic equations and Maxwell’s EM relations. This coefficient describes the coupling between electric and mechanical fields. These are expressed in terms of the fluid-solid ratios and the so-called (frequency-dependent) electrokinetic coupling coefficient. Each wave mode also has a specific ratio of electric potential and solid displacement potential. These are derived and expressed also in terms of generalized elastic coefficients and effective densities. Each of the wave modes has a specific fluid-solid amplitude displacement ratio. The electrokinetic dispersion relations, which give wave speed and intrinsic attenuation of each wave, are expressed in terms of generalized elastic coefficients and the effective densities. The reformulated theory predicts the existence of four wave modes within a fluid-saturated porous medium: fast and slow P-waves, a shear wave and an EM-wave. The reformulation employs effective frequency-dependent densities, in which both viscous and electrokinetic coupling are comprised. ![]() In this thesis, electrokinetic theory is reformulated along the lines sketched by Biot (1956a,b). Electroseismic counterparts of these fields exist as well. These are called the coseismic and interface response fields, respectively. Validating electrokinetic wave theory is therefore of paramount importance.Įlectrokinetic theory predicts the existence of two seismoelectric effects: (1) a coseismic (electric) field that is coupled to seismic waves, and therefore propagates with seismic wave velocity, and (2) a seismic wave that traverses an interface with a contrast in electrical or mechanical properties and produces electromagnetic (EM) signals that propagate outside the support of the seismic waves with much higher EM-wave speeds. Electrokinetic conversions can potentially be used as an effective means of detecting hydrocarbon reservoirs: it inherently combines seismic resolution with electromagnetic hydrocarbon sensitivity. Inversely, the theory predicts that electromagnetic waves generate mechanical/seismic signals (electroseismic effect). It predicts that seismic waves disturb the fluid excess charge, thereby creating an electric streaming current (seismoelectric effect). Electrokinetic theory describes coupled seismic and electromagnetic wave propagation. Within the double layer, charge is redistributed, creating an excess electrical charge in the fluid along the boundary. This coupling arises because of the electrochemical double layer, which exists along the solid-grain/fluid-electrolyte boundaries of porous media. Coupled seismic and electromagnetic wave propagation is studied theoretically and experimentally.
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