Field evaluation of borehole electrical impedance tomography
This joint project between the University of Bonn, Geotomographie GmbH, ZEL and IBG 3 funded by BMBF in the framework of the Geotechnologien programme (2011-2013) is motivated by research over the last decade which has proven the potential of spectral induced polarization (SIP) to characterize soils with respect to pore-fluid chemistry and saturation, mineral surface properties, texture, and permeability. Given the parallel establishment of electrical impedance tomography (EIT) as a subsurface imaging tool in recent years, the implementation of EIT in a full spectroscopic manner now represents a conceptually straightforward, highly desired, yet challenging methodological extension.
Research in Jülich focuses on to main tasks in this project:
- Successful EIT requires broadband spectral information in the range of 1 mHz to 1 kHz with a high phase accuracy in the order of 1 mrad. Unfortunately, capacitive and inductive coupling effects are superimposed with the subsurface response and typically start dominating the EIT signal above 10 Hz. This limits the useful frequency band of available instruments to below 10 Hz, which in turn severely limits soil characterization capabilities. In this task led by the ZEL, the different coupling effects are quantitatively described in order to correct field EIT measurement to obtain the required accuracy in a broad frequency range.
A prerequisite for the establishment of EIT as a new imaging technology is a thorough evaluation and validation on both synthetic and field data. These efforts are led by IBG 3 and rely on the wealth of information available for the Krauthausen test site, which has been extensively characterized in the past, and where independent SIP measurements are available.