Electromagnetic (EM) techniques are nowadays routinely used in geodynamic research or to characterize hydrocarbon reservoirs in offshore petroleum exploration. Moreover, distinct electrical conductivity properties make EM techniques prime geophysical tools to characterize saline aquifers for geothermal reservoirs or CO2 storage. Still, the interpretation techniques need to be improved. With the Multi-EM project we attempt to enhance resolution properties by combining electromagnetic diffusion and DC-geoelectric methods in a multi-scale environment. This collaborative effort combines research groups from applied and numerical geophysics, information technology and numerical mathematics.
The electrical conductivity of the subsurface can be explored using a variety of techniques. In the framework of the Multi-EM project we focus on the natural source magnetotellurics (MT), controlled source electromagnetics (CSEM), DC resistivity method and transient electromagnetics (TEM). The resolution power of the individual method depends on the experimental design, the strength, geometry, and signature of the source field, and the characteristics of the subsurface current system.
Joint multi-scale multi-method EM inversion strategies aim at combining the strengths of different methods to obtain enhanced resolution power. The combination of various sensitivity patterns is expected to result in (i) better coverage of the model space (ii) more complete and better resolved reconstructions of the subsurface conductivity structure and (iii) reduction of model ambiguities.
Considering the enormous numerical complexity of multi-method three-dimensional inversion, the new algorithms are designed for parallel computing architectures integrating memory and run-time efficient state-of-the-art numerical simulation techniques.