Three-dimensional Multi-Scale and Multi-Method Inversion to Determine the Electrical Conductivity Distribution of the Subsurface Using Parallel Computing Architectures (Multi-EM)

For tomographic imaging of a single physical parameter, the electrical conductivity, a number of well-proven techniques are available. In this project, we combine geoelectric methods (direct current DC), transient electromagnetics (TEM), natural-source magnetotellurics (MT) and controlled-source magnetotellurics (CSMT) (see Fig. 1). The resolution power of the individual methods depends on the experimental design, the strength, geometry, and frequency content of the source fields and the characteristics of the induced current systems. Multi-scale, multi-method inversion strategies yield complementary but usually higher sensitivities when compared with existing inversions of the individual methods. Hence, a combina1. Objectives Geophysical methods are applied to investigate the Earth’s interior. We obtain models of the Earth by imaging physical parameters such as density, electrical conductivity, or elastic properties using a range of techniques. Here, we consider geophysical techniques exploiting natural and controlled-source electromagnetic (EM) fields to reconstruct the electrical conductivity structure at depth. During the last years, these techniques have experienced rapid development for exploration purposes of the drillable subsurface. For instance, active controlledsource electromagnetic (CSEM) techniques are now frequently used together with seismic techniques to characterize resistive hydrocarbon reservoirs in offshore petroleum exploration. Deep saline aquifers exhibit high electrical conductivities and constitute one of the prime targets for electrical imaging methods, making these techniques one of the most important geophysical tools to characterize target horizons for CO2 storage or geothermal reservoirs.