Numerical analysis of seismoelectric wave propagation in spatially confined geological units

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ABSTRACT

Using numerical modelling, we investigate the evolution of seismoelectric effects induced by seismic excitation in spatially confined lithological units. Typical geometries represent clay lenses embedded in an aquifer or petroleum deposits in a host rock. In fluid-saturated rocks, seismic waves can generate electromagnetic fields due to electrokinetic coupling mechanisms associated with such processes in the vicinity of the fluid-mineral interface. Two seismoelectric phenomena are investigated: (1) the co-seismic field associated with the seismic displacement at each point in a subsurface and (2) the interface response generated at layer boundaries. Our modelling uses a simplified time-domain formulation of the coupled problem and an efficient 2D finite-element implementation. To gain insight into the morphogenetic field behaviour of the seismoelectric effects, several numerical simulations for various target geometries were treated. Accordingly, we varied both the thickness of the confined units and the value of the electrical bulk conductivity in porous media. Analysis of these effects shows differences between interface responses for electrically conductive versus resistive units. So the pertinent contrast in electrical bulk conductivity controls the shape and structure of these seismoelectric conversion patterns. Moreover, the seismoelectric interface response captures both the petrophysical and geometrical characteristics of the geological unit. These models demonstrate the value of using seismoelectric interface response for reservoir characterization in either hydrogeological or hydrocarbon exploration studies.

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