Investigations into the Mechanisms of Spectral Induced Polarization: Laboratory Studies on the Response of Non-Conductive and Conductive Inclusions

Spectral induced polarization (SIP) is a non-invasive, frequency-domain geophysical technique that is sensitive to the resistive and capacitive properties of the subsurface. While historically utilized for the exploration of economically valuable mineral deposits, the application of SIP has expanded to include environmental monitoring, hydrogeological characterization, and the tracking of biogeochemical processes. Despite this broad utility, the interpretation of complex conductivity spectra remains challenging due to the overlapping effects of multiple underlying polarization mechanisms and persistent errors in data collection. This dissertation presents a series of controlled laboratory investigations designed to better understand SIP signals associated with non-conductive and conductive inclusions and to improve the accuracy of laboratory SIP measurements. First, we investigate the SIP response of calcite precipitation using a novel double-diffusion method across various gel-saturated media, including pure gel, quartz sand, and a sand-magnetite mixture. Our findings demonstrate that calcite crystals in isolation are unlikely to produce a significant SIP response. Instead, we show that the primary driver of changes in the complex conductivity during precipitation is the physical blocking of pores, which exerts a significant influence on the SIP response of geologic media, particularly when disseminated semi-conductors are present. Second, we provide a simple a simple alternative to correcting high frequency (above 1 kHz) phase errors associated with the potential electrode impedance that adversely impact four-electrode SIP measurements. We propose the use of simultaneous two and four-electrode measurements on a single sample holder utilizing low impedance coiled silver silver-chloride (Ag-AgCl) electrodes. Under a certain set of conditions, it is possible to utilize the phase angles measured with two-electrodes to correct those measured with four thereby improving data accuracy past 1 kHz. Finally, we study faradaic and non-faradaic polarization mechanisms in conductive spheres. We achieve this by comparing the SIP response of stainless-steel spheres that are freely disseminated within a conductive gel versus embedded within an insulating disk. In addition, we test the effect of altering the current density on the complex conductivity spectra. Embedded spheres show an SIP response that is both stronger and occurs at a distinctly lower frequency range. Embedded spheres also showed significant non-linearity in response to increases in current density not seen in the freely disseminated spheres.