Influence of Inner Surface Roughness on the Spectral Induced Polarization Response—A Numerical Study

AbstractSpectral induced polarization (SIP) laboratory measurements on water‐saturated rocks show a strong correlation between the electrical polarization strength and the inner surface area of rocks. We investigate the influence of inner surface roughness on the SIP response by simulating the frequency‐dependent complex conductivity of micro‐scale rock models. Starting with smooth grain models, we introduce surface roughness using two different approaches: increasing the surface roughness in a fractal‐like manner, and creating random surface structures, resulting in more natural‐looking surfaces. We find that surface roughness has two distinct effects on the SIP response: (a) a shift in the position and magnitude of the primary relaxation frequency to lower frequencies and lower magnitudes, respectively, and (b) the formation of secondary polarizations above the polarization frequency of the primary polarization. We also compare the relaxation time and normalized chargeability obtained by Debye decomposition and the imaginary conductivity at 1 Hz of our models with mechanistic models and empirical relations. We point out the congruences and offer explanations for the discrepancies between our models and the empirical observations. We conclude that the results of our study are applicable to real rocks and that the SIP method has the potential to detect inner surface roughness. However, the SIP method it not able to discriminate between signals from rough particles and a distribution of smooth particles.Plain Language Summary: The spectral induced polarization method measures the electrical conductivity of the subsurface at depths of investigation ranging from a few dm to several 100 m. The potential of the method to detect mineral resources, contamination, microbial activity, etc. makes it a promising tool for today's environmental challenges. However, due to the complexity of the underlying physical and chemical processes the interpretation of SIP measurements often remains qualitative. Mathematical and mechanistic models used to describe the processes are usually simplified with respect to geometry, chemistry, and physical properties. In this study, we use computer simulations to investigate the surfaces of spherical particles (grains). After simulating the SIP response of models with smooth and rough surfaces, we analyze the influence of surface roughness on the SIP response. We find that surface roughness causes distinct changes in the SIP response compared to the smooth grain. However, we also find that this introduces an ambiguity in the interpretation of SIP data.Key Points: Inner surface roughness of rocks has substantial impact on spectral induced polarization response Surface roughness shifts the primary polarization peak to lower frequencies Surface roughness causes additional polarizations above the primary peak frequency https://doi.org/10.5281/ZENODO.704972

Berichtsband 1984-1987. Sonderforschungsbereich 69 - Geowissenschaftliche Probleme in ariden Gebieten, Entwicklung und Potential kratonaler Grossstrukturen, Technische Universitaet Berlin

The results of the projects of the Special Field of Research 69 are completely published in English in ''Berliner Geowissenschaftliche Abhandlungen, vol. 75''SIGLETIB: FR 167 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman