An improved liquid-liquid extraction technique to determine shale wettability

Abstract

Quantifying the wettability of shales is very important for reservoir evaluation and petroleum production prediction. However, differences in wettability of the same sample can occur using conventional methods, such as contact angle measurement and spontaneous imbibition experiments, due to the heterogeneity of shales with comingling presence of μm-sized organic matter and minerals. In this study, an improved liquid-liquid extraction (LLE) technique using particles is presented to determine the wettability of four lacustrine shales, with high-purity graphite (hydrophobic) and quartz (hydrophilic) selected as the reference materials. The effectiveness of this improved technique is demonstrated by a good repeatability in shales, graphite and quartz. In addition, a simple model of a spherical particle at the two-phase liquid interface was presented to analyze the forces on the particle and explain the particle behavior. Several factors such as particle sizes, experimental procedure, and different liquids were found to affect the LLE results, especially for heterogeneous water-wet and zwittering shales. Experimental temperature is also a critical factor for LLE results. Although some factors have a negligible effect on the results of LLE tests for oil-wet materials, the use of uniform and consistent conditions is recommended in the LLE experiments.