Seismic to Electric Conversion: a Tool for Subsurface Characterization

Present approaches for subsurface imaging rely predominantly on seismic techniques, which alone do not directly capture fluid-specific properties and related mechanisms. On the other hand, electromagnetic (EM) measurements add constraints on the fluid phase through, for example, electrical conductivity. However, EM signals alone do not offer direct information of solid properties. In the recent years, there have been many efforts to combine both seismic and EM data for exploration geophysics. The most popular approach is based on joint inversion of decoupled seismic and EM data. Seismoelectric effects are triggered by pore fluid movements with respect to the solid grains. By analyzing fully coupled poroelastic seismic and EM wave equations, one can capture a pore scale behavior and more accurately resolve both solid and fluid properties.

To model the seismoelectric response, Biot's poroelastic seismic wave equations and Maxwell's electromagnetic wave equations are coupled electrokinetically. These equations are solved using a spectral-element method (SEM). The SEM, in contrast to finite-element methods (FEM) uses high degree Lagrange polynomials. Not only does this allow the technique to handle complex geometries similarly to FEM, but it also retains exponential convergence and accuracy due to the use of high degree polynomials.

We will also discuss the next step toward quantitative subsurface characterization through full waveform inversion based on adjoint method.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.