Resumo

GAUZELLINO, Patricia M; ZYSERMAN, Fabio I  e  SPATH, Federico G. E.. Respuesta de geófonos a campos electromagnéticos. Geoacta [online]. 2010, vol.35, n.2, pp.54-66. ISSN 1852-7744.

Electro-osmosis in saturated porous media is the physical phenomenon in which an electrical potential variation gives rise to fluid flow. The reciprocal phenomenon, called electro-filtration effect, is an electrical charge flux originated by pressure gradients in the pore fluid. The quotient between electrical potential and pressure gradient represents the electrokinetic coupling coefficient. In 1999 a proof field was performed, where seismic waves were generated by electromagnetic source. In this work it is explained why happen these phenomena. The equations that govern the coupled seismic and electromagnetic wavefields are presented and the transport coefficients (electrical conductivity, dynamic permeability and electrokinetic coupling coefficient) are analyzed. Some assumptions on the model allow solve a simplified set of equations where Maxwell's equations are decoupled from Biot's equations. For the Maxwell's equations it is possible to separate the electromagnetic fields in primary and secondary parts. The former can be found analytically, while to find the latter a numerical procedure is employed. Dissipative effects in porous media can be included by using complex viscoelastic moduli in space-frequency domain. Also, it is important notice that pressure gradients in the pore fluid are correctly represented if the grid points are calculated using diffusive skin depth of 55 the Biot slow wave. Numerical examples illustrate the capabilities of the modeling for detecting reservoir fluid contacts.

Palavras-chave : Electroseismic; Maxwell Equations; Biot Equations; Poro-viscoelastic Medium.

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