Advancements of induced polarisation theory in sediments

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The estimation of hydraulic parameters with geophysical methods is a research area of fundamental importance, e.g. for groundwater exploration and management, for geothermal energy, and for environmental problems. Spectral induced polarization is a promising method that measures the frequency dependent electrical conductivity of the subsurface. In principle, hydraulic parameters may be estimated from electrical conductivity through empirical relationships derived in the laboratory. The empirical relationships, however, often depend on the material and lack general applicability, or they have large error margins. Within this project, we investigate the theoretical foundations of the relationships between electric and hydraulic properties of porous media. During the course of the ongoing project, an existing semi-analytical model that describes the impedance of a cylindrical pore system was extended into an impedance network. The extension allows to incorporate measurable petrophysical parameters, such as porosity, specific internal surface, or pore radii distribution, into the model. We succeeded to simulate several characteristic properties of measured laboratory data, including features that cannot be explained with conventional approaches. Within the proposed prolongation, we will further improve the model by modifying some of the chosen parameterizations, with the aim to quantitatively fit measured impedance spectra. We also will extend the comparison with measured data to larger data sets in order to test hypotheses resulting from the theory.