Systematic Investigation of Fluid-Fluid Displacement in Mixed-Wet Porous Media

Fluid-fluid displacement in porous media occurs in many natural and industrial processes such as geological CO2 storage and enhanced oil recovery. It has been recognized that wettability plays an important role in the displacement process. Thanks to decades of research, we now have a good understanding of fluid-fluid displacement in porous media with uniform wettability. In contrast, our knowledge of fluid-fluid displacement in porous media with heterogeneous wettability (i.e., mixed-wet) is much less complete, although mixed-wet states are common in many subsurface processes.

Here, we study fluid-fluid displacement in mixed-wet micromodels. The micromodels are made of an oil-wet polymer whose wettability can be locally tuned to become water-wet via deep UV exposure. Our experiments show that the mixed-wet pores exert fundamental control over the macroscopic displacement pattern and that the incorporation of the capillary entry pressures at mixed-wet pores into a dynamic pore-network model reproduces the experiments. The pore-network model that we developed is a computationally efficient tool to study fluid-fluid displacement in mixed-wet porous media. We use this framework to simulate fluid-fluid displacement in hundreds of different mixed-wet micromodels by varying the size, contact angle, and spatial distribution of the water-wet clusters (Figure).