Effect of wettability on the variation of resistivity characteristics during diesel oil infiltration into the unsaturated zone.

When diesel oil infiltrates into the formation of the unsaturated zone under certain pressure conditions, a water–oil–gas multi-phase flow system is formed and the resistivity of the contaminated zone changes continuously. Most findings in the fresh diesel-contaminated zone support the high resistivity anomaly feature. Still, previous studies have found that resistivity is lower in the fresh contaminated zone than in the background clean soil layer due to altered soil wettability. This study aims to investigate the link between wettability traits and changes in resistivity. It employs varying sand particle sizes and moisture levels for simulation experiments, focusing on diesel oil infiltration in unsaturated strata. The research observes alterations in wettability and soil resistivity during this infiltration process. In addition, it examines the connection between wettability and saturation exponent changes using Archie's formula and the saturation exponent (n). The results showed that the change of resistivity in the process of diesel infiltration in the unsaturated zone was mainly influenced by the initial water saturation and wettability of the soil. Meanwhile, the wettability of soil particles underwent a dynamic change process from water-wet to water–oil mixed-wet and oil-wet. In addition, the saturation exponent n increased, then decreased, and then increased again, finally stabilizing. The results unveiled the characteristics of resistivity and wettability changes during the initial evolution of the freshly contaminated source area. [ABSTRACT FROM AUTHOR]