Dielectric permittivity measurements are used across various geoscience-related applications for the purpose of determining soil moisture content, characterizing soil and rock properties, and monitoring geoprocesses. However, their accuracy is often compromised by the diverse composition of natural brines. A key aspect of interpreting dielectric permittivity measurements is having a reliable model for the saturating brine solution. It is unclear whether the existing models, typically based on single-salt NaCl solutions, fail to account for diverse ionic mixtures. We address this gap by developing a comprehensive dielectric model from an extensive experimental dataset of eight salts (i.e., NaCl, KCl, CaCl 2 , MgCl 2 , K 2 CO 3 , K 2 SO 4 , LiCl, NaBr). This dataset includes more than 200 measurements of both single salt solutions and complex mixtures. The results demonstrate that for brines dominated by Na + , Ca 2+ , and Cl - ions, a simple NaCl-based model can be used in practical applications in the absence of extended ionic analysis when the salt concentration is below 100 kilo parts per million (kppm). However, at salt concentrations above this threshold, the permittivity of the aqueous salt solution needs to be determined by considering the specific concentration of each constituent ion. For diverse multi-component brines, we propose a linear mixing rule that predicts static permittivity with a mean absolute percentage error of 0.7%. This work provides an experimentally grounded framework for bulk brine permittivity under controlled laboratory conditions (20.2 ± 0.1 °C, atmospheric pressure), serving as a foundational baseline for calibration standards used in hydrology, geosciences, and petroleum engineering applications.
Azizoglu et al. (2026) studied this question.