Experimental Investigation of Shale Wettability Characterization

Abstract Shale wettability has been extensively studied through contact angle measurements and imbibition tests. Previous research has predominantly focused on surface interactions between air and water or air and oil, considering factors such as temperature, pressure, ionic strength, pH, and mineral composition. However, studies involving shale wettability between air and liquid have primarily emphasized its preferential affinity toward air or liquid phases rather than the oil-water phase, as governed by Young's equation. This limited perspective has led to misunderstandings regarding the critical role of shale wettability in reservoirs, which needs further investigation. This study aimed to characterize shale wettability through various methods. Contact angle measurements indicated that the wettability of samples was complex, with distinct wettability observed within a single sample. Additionally, the sequence of liquid contact influenced shale behavior wettability. When water first contacts the shale surface, the material exhibits a stronger affinity for water compared to oil. Conversely, initial contact with oil results in a higher affinity for oil. Meanwhile, the duration of fluid contact played an important role, as prolonged interaction induces aging effects that increase the affinity of shale for the contacting fluid over time. Spontaneous imbibition tests showed that all shale samples exhibit mixed wettability characteristics despite initially appearing water-wet based on contact angle measurements. These findings demonstrated the limitations of relying solely on contact angle measurements to evaluate shale wettability. A more comprehensive approach using both contact angle analysis and imbibition testing is recommended for understanding shale wettability. This approach provides deeper insights into surface interactions between shale and fluids, particularly in reservoirs.