An investigation of the petrophysical properties controlling the spectral induced polarization signatures of sedimentary rocks
Creators: name: Peshtani, Klaudio
Publisher: name: No Publisher Supplied
Year: 2024

description: The induced polarization (IP) method is a non-invasive electrical geophysical technique that detects variations in properties that influence various subsurface processes. Initially deployed for mineral exploration in the early 1900s, the IP method has evolved over recent decades into a powerful tool for hydrogeological and environmental investigations, aiding in interpreting the properties that control the flow and transport of fluids within rocks. This dissertation focuses on the application of the induced polarization method to enhance the understanding of the petrophysical properties of porous sedimentary rocks that are critical for determining the hydraulic characteristics of the near surface. First, we demonstrate that magnetic susceptibility measurements exhibit a surprisingly strong correlation with IP parameters (imaginary conductivity and normalized chargeability), utilizing an extensive dataset of 241 samples, including sandstone, carbonate, and arenite. By combining magnetic susceptibility with pore geometric descriptors (PGD), which are typically used to model IP measurements, we significantly improve the empirical prediction of IP measurements compared to using PGD terms alone. This discovery indicates that even minimal concentrations of magnetic minerals in rocks, often presumed to be devoid of electron-conducting minerals, can markedly affect IP measurements. Next, we utilized the IP method to investigate the electrical properties that control the petrophysical characteristics of 23 mudstone rocks, which have been infrequently reported. Our findings reveal that the permeability and IP parameters in mudstones are primarily controlled by their effective porosity, inversely related to the formation factor. The modified Hagen-Poiseuille equation accurately predicts the permeability of these mudstones, characterized by a nearly constant effective pore radius. This study underscores the significant influence of the IP response, and consequently, permeability, in fine-grained sedimentary rocks. Finally, we assess the relationship between IP parameters (imaginary conductivity and normalized chargeability) and surface conductivity across a dataset of 98 sandstones, carbonates, and mudstones. A strong linear correlation is observed, and the coefficient describing this IP-surface conductivity relationship, known as the proportionality factor, is utilized in an attempt to estimate the apparent formation factor. This approach aligns with previously suggested mechanistic models aimed at improving the interpretation of field-scale resistivity measurements. The estimation of the formation factor is most accurate when applying a proportionality factor value determined from each individual subgroup. In contrast, using external coefficient values as a standard yields poor estimation result. This study emphasizes the challenges associated with using IP measurements to improve the prediction of petrophysical parameters of resistivity measurements.