Insight into the Injection Rate Effects on Residual Liquid Film in Tight Sandstone Nanopore

Waterflooding in tight reservoirs is a key focus in the recent oilfield development, making it essential to accurately assess the injection rate effect in tight sandstone. This study investigates the relationship between injection rate and residual liquid film (water and oil film) thickness, as well as the underlying mechanisms, by conducting oil-driven water experiments combined with molecular dynamics simulations. The morphology of the liquid film formed under different injection rates serves as the primary focus of this research. The experimental results indicate that as the oil injection rate increases, the volume of stagnant water and bound water gradually decreases and stabilizes. Molecular dynamics simulations results reveal that the displacement process can be categorized into three stages: a rapid injection stage, a slow injection stage, and a smooth injection stage. In the oil-driven water system, the thickness of the final water film is more uniform. As the injection rate increases, the recovery rate gradually decreases. However, once the injection rate reaches a certain threshold, the rate of decline in recovery rate slows down. This study provides a theoretical foundation and reference data for selecting optimal injection rates in waterflooding operations for tight reservoirs, contributing to improved recovery rate and velocity.