Electrical Conductivity and Permittivity of Porous Media: Origin, Measurements, and Implications.

Electrical sensing technologies have advanced our ability to infer and evaluate the hydraulic characteristics of porous media that are otherwise inaccessible to direct measurement. Such challenges are particularly prevalent in geo-porous materials such as rocks and soils found in remote regions, harsh environments, or beneath the Earth's surface. Noninvasive sensing and characterization of these materials are indispensable preliminary steps for water-energy nexus activities, including extraction processes (e.g., desalination, groundwater utilization, fossil fuel and geothermal exploration and production) and mitigation efforts (e.g., sediment transport monitoring, contaminant management, and carbon or hydrogen capture, utilization, and storage). These electrical properties are measurable only if the material under investigation possesses an electrical charge and is polarizable. Electrical polarization refers to the relative displacement between positive and negative charges. This raises several critical questions: (i) In what ways can porous media acquire electrical charge and exhibit polarization? (ii) How can their electrical properties be measured both in laboratory and field environments? (iii) What frameworks can be used to interpret the observed electrical properties? (iv) How can we assess the reliability and validity of these interpretations in relation to the hydraulic and physical state of the porous media? This study aims to systematically investigate these questions through a comprehensive synthesis of existing literature and the integration of newly obtained experimental data.