Combination of electromagntic methods

Multi-EM Multi-Method Inversion to Determine the Electrical Conductivity Distribution of the Subsurface Using Parallel Computing Architectures

Multi-EM Summary 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 quasi-static geoelectric potential field and electromagnetic diffusion methods in a multi-scale environment. This collaborative effort combines research groups from applied and numerical geophysics, information technology and numerical mathematics.

Introduction The electrical conductivity of the subsurface can be explored using a variety of techniques. Here, we focus on the DC resistivity method, transient electromagnetics (TEM), natural source magnetotellurics (MT) and controlled source electromagnetics (CSEM).

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. The table below compiles the pros and cons of each method along with typical application areas to show the diversity of EM exploration.

Multi-method, multi-scale, multi-dimensional inversion 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 runtime efficient state-of-the-art numerical simulation techniques.

Synthetic experiment a) ”True model” b) MT resolves the conductive parts (red) but fails to image the thin resistive (blue) sheet c) CSEM can resolve resistive structures better, whereas conductor is not well resolved d) Joint inversion combines the advantages of the individual methods and results in a model close to the “True model”.

Technological potential and advantages: - High-resolution electrical image of the subsurface - Variety of geoengineering and geoscientific applications - Cost effective subsurface imaging - Complementary to seismic exploration techniques

Inquiry for cooperation:

Contact person Research project Multi-EM

Dr. Oliver Ritter telephone +49 (0331) 28812 57 oliver.ritter@gfz-potsdam.de Prof. Klaus Spitzer telephone +49 (03731) 392722 klaus.spitzer@geophysik.tu-freiberg.de

The field of application is not restricted. The multi-scale approach offers a wide range of possibilities even outside geo-related fields.

For further questions, please feel free to contact us.

Coordination office GEOTECHNOLOGIEN Alexandra Scherer telephone +49 (331) 288-1074 kontakt@geotechmarket.de www.geotechmarket.de

The project Multi-EM was supported by the GEOTECHNOLOGIEN program of the Federal Ministry of Education and Research.