Influence of Salt Type and Concentration in Brine on the Dielectric Permittivity of Rocks

The dielectric properties of the saturating brine significantly influence dielectric permittivity measurements in rock-fluid systems. Therefore, a reliable interpretation of dielectric data requires a fundamental understanding of how the properties of the saturating brine (e.g., salt type and concentration) affect the permittivity of rocks. The objective of this paper is to highlight and explain the combined impacts of brine dielectric properties (including a wide range of salt types and concentrations, and compositions of salt mixtures), porosity, and pore structure on the dielectric permittivity of rocks. and interfacial polarization was limited, allowing for reliable water saturation assessment using the Complex Refractive Index Model (CRIM) without including the brine type and concentration in the evaluation at 1 GHz. Furthermore, the rocks saturated with KCl brine exhibit the highest relative permittivity, whereas those saturated with CaCl2 brine exhibit the lowest. When the saturating brine is NaCl at 100 kppm, the relative difference between the actual water-filled porosity and the estimated one using CRIM is 10% for BS, 35% for AC, and 65% for HS at 1 GHz. As the salt concentration increases to 200 kppm, the relative difference between the actual and estimated water-filled porosity increases to 28% in BS6, 46% in AC8, and 127% in HS8. The impact of salt concentration is greater in the documented complex carbonate rocks (HS and AC) compared to the case of BS. The main contribution of this work is to expand the fundamental understanding of dielectric behavior in multi-salt, multi-phase systems and enhance We numerically simulate the dielectric permittivity of the interpretative framework for petrophysical pore-scale 3-dimensional micro-computed tomography scans of actual rock samples over a frequency range of 20 MHz to 3 GHz. The frequency-domain numerical simulations solve Maxwell's equations under the quasistatic approximation and use the images of rock samples and the dielectric properties of rock constituents (i.e., matrix, and brine) as inputs. We experimentally determine the dielectric permittivity of various brine solutions (e.g., NaCl, KCl, and CaCl2) and their mixtures at different concentrations ranging from 10 to 200 kilo parts per million (kppm) using a coaxial probe and a network analyzer at 20.2 ± 0.2 °C and 1 atm. The rock samples are taken from Berea sandstone (BS), Austin Chalk (AC), and Happy Spraberry (HS) formations. We perform sensitivity analysis to evaluate the conditions under which changes in brine composition may (or may not) be neglected. We observed that the relative permittivity of rock samples varies significantly with changes in saturating brine. At a salt concentration of 10 kppm, differences in relativepermittivityamongvariousbrineswereminimal, evaluation in complex formations. In conclusion, the results suggested that the impact of salt type and concentration is significant in rocks with complex pore structure. Assuming a constant permittivity for CaCl2 brine may be acceptable for interpreting dielectric measurements in BS. However, this assumption yields unreliable water-filled porosity estimates when different salt types are present or when applied to more complex rocks. Therefore, an accurate quantification of dielectric properties of the saturating brine is necessary for reliable water saturation assessment from dielectric permittivity measurements.