Immiscible fluid displacement in a porous medium*

Understanding the physics of immiscible fluid displacement within porous media is of great

importance in many fields of study, for example, geological CO2 sequestration, hydrology, and enhanced oil recovery. In these applications, it is important to understand the fundamental laws of immiscible fluid displacement in the complex pore network to optimize the fluid entrapment depending on the application. In this study, we investigate experimentally the fluid entrapment process in an idealized model of the porous media called pore-doublet model for a fluid pair of silicone oil (as the wetting fluid) and water (as the non-wetting fluid). Specifically, we study the drainage process of non-wetting fluid displacing the wetting fluid for a Weber number (based on the height of the channel) of 0.0003 to 0.03 for three different pore geometries. It was found that increasing the Weber number leads to increased entrapped volume of the wetting fluid in the pore doublet model. However, beyond a critical Weber number of ~0.007, the displacing fluid pierces through the pockets of the entrapped fluid leading to an instability of the trapped fluid. For these cases, the trapped oil is washed off almost completely. The findings from this study will be useful not only for understanding the fundamental laws of these complex flows, but also for improving the accuracy of predictive numerical models for which resolution of contacts, thin films and contact line motions is an ongoing challenge.