Indication of wettability from dielectric measurements on partially saturated rocks using effective medium models

We used two effective medium models to fit dielectric measurements on a limestone for water-wet (WW) and mixed-wet (MW) cores. The models were based on a bimodal distribution of matrix and hydrocarbon inclusions dispersed in a water host, either as one effective inclusion (bimodal model) or as separate entities (Feng-Sen bimodal). We observed that wettability has a significant effect on the shape factors of the inclusions. These shape factors were the apparent cementation factor in the bimodal and the shape factor for hydrocarbon in the Feng-Sen bimodal. The apparent cementation factor obtained in the bimodal model combined the effects of matrix and hydrocarbon in the water phase tortuosity, and we got higher values for MW than WW rocks of similar pore structure and lithology. It also varied with water saturation. The shape factor for hydrocarbon in the Feng-Sen bimodal model showed how the shape distribution of hydrocarbon affected the water phase tortuosity. It got higher values for MW than WW rocks of similar pore structure and lithology and also varied with water saturation. This variation can be interpreted as a change in the shape of the hydrocarbon ganglion. Because these shape factors are sensitive to water saturation and wettability, we need to be careful when only using them to solely interpret wettability. We expect that this study can be useful in identifying parameters from dielectric measurements that are sensitive to wettability.