Influence of Temperature and Wettability on Dielectric Response of Calcite

Oil-water-mineral interactions play a critical role on wettability. There is an extensive amount of research focused on quantifying the influence of wettability on dielectric properties. However, a full understanding of the relationship between the structure and mobility of oil and water molecules (clusters) within the pores of the mineral (e.g. calcite) has yet to be developed. To this end, here we demonstrate the use of dielectric spectroscopy as an effective method to characterize and understand the complex interactions in the calcite-water-oil system. The dielectric response of water-oil mixture in porous calcite is studied from low to high-frequency (mHz – MHz) and at various temperatures (273K – 553K).

In the presence of water, the dielectric response gives rise to anomalous low-frequency dispersion (ALFD). Which follows two power-law regions, separated by a transition frequency. The response is rationalized in terms of hopping transport. Additionally, we measured the dynamic dielectric response on untreated and aged calcite in partially saturated conditions with different salinities and compositions. In the presence of oil, the dielectric dispersion and their corresponding transition frequency were shifted to lower frequencies and lower susceptibility values. This suggests less connectivity between water clusters and, where trapped oil is preventing direct contact between water and calcite grains. We also demonstrated that power-law exponents can be used to understand the fractal structure of inclusions. Whereas untreated calcite followed the predicted behavior of single fractal clusters, aged calcite followed that of percolation of many clusters. A flat response is observed in the case of preheated calcite which indicates that temperature and dielectric dispersion are related, although the major contributor is water content and depends on both structural arrangement and mobility of water clusters in the disordered system. Furthermore, impedance measurements are used to determine the surface roughness or the fractal dimension (d_s) and the associated structural arrangement. The work demonstrates the utility of dielectric spectroscopy as an efficient tool for characterizing structural arrangements and behavior in complex systems such as water-oil mixtures in porous media.